diff --git a/.php-cs-fixer.php b/.php-cs-fixer.php
index 62d1ac7f7..ed2e6cf2b 100644
--- a/.php-cs-fixer.php
+++ b/.php-cs-fixer.php
@@ -71,7 +71,7 @@ return $config->setRules([
         'random_api_migration' => true,
         'ternary_to_null_coalescing' => true,
         'phpdoc_to_param_type' => true,
-        //'declare_strict_types' => true,
+        'declare_strict_types' => true,
 
         // TODO php 7.4 migration (one day..)
         // 'phpdoc_to_property_type' => true,
diff --git a/src/Composer/Autoload/AutoloadGenerator.php b/src/Composer/Autoload/AutoloadGenerator.php
index 5485565e0..0ddcc9df1 100644
--- a/src/Composer/Autoload/AutoloadGenerator.php
+++ b/src/Composer/Autoload/AutoloadGenerator.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Autoload/ClassMapGenerator.php b/src/Composer/Autoload/ClassMapGenerator.php
index 84f946440..fa687d101 100644
--- a/src/Composer/Autoload/ClassMapGenerator.php
+++ b/src/Composer/Autoload/ClassMapGenerator.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Autoload/PhpFileCleaner.php b/src/Composer/Autoload/PhpFileCleaner.php
index f1e6048b2..d6a840b68 100644
--- a/src/Composer/Autoload/PhpFileCleaner.php
+++ b/src/Composer/Autoload/PhpFileCleaner.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Cache.php b/src/Composer/Cache.php
index 0f8dc6aa4..c6e2585aa 100644
--- a/src/Composer/Cache.php
+++ b/src/Composer/Cache.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/AboutCommand.php b/src/Composer/Command/AboutCommand.php
index 80d9a9caa..29dc718e7 100644
--- a/src/Composer/Command/AboutCommand.php
+++ b/src/Composer/Command/AboutCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/ArchiveCommand.php b/src/Composer/Command/ArchiveCommand.php
index db302b865..0a35f6f28 100644
--- a/src/Composer/Command/ArchiveCommand.php
+++ b/src/Composer/Command/ArchiveCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/BaseCommand.php b/src/Composer/Command/BaseCommand.php
index c06e3ffa5..930cde9d5 100644
--- a/src/Composer/Command/BaseCommand.php
+++ b/src/Composer/Command/BaseCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/BaseDependencyCommand.php b/src/Composer/Command/BaseDependencyCommand.php
index f1ebe4277..064b26d31 100644
--- a/src/Composer/Command/BaseDependencyCommand.php
+++ b/src/Composer/Command/BaseDependencyCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/CheckPlatformReqsCommand.php b/src/Composer/Command/CheckPlatformReqsCommand.php
index 54e1e9ba1..6854ee690 100644
--- a/src/Composer/Command/CheckPlatformReqsCommand.php
+++ b/src/Composer/Command/CheckPlatformReqsCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/ClearCacheCommand.php b/src/Composer/Command/ClearCacheCommand.php
index e7c15de31..e2ba384d3 100644
--- a/src/Composer/Command/ClearCacheCommand.php
+++ b/src/Composer/Command/ClearCacheCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/ConfigCommand.php b/src/Composer/Command/ConfigCommand.php
index 3285fd3b4..b20a4ba81 100644
--- a/src/Composer/Command/ConfigCommand.php
+++ b/src/Composer/Command/ConfigCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/CreateProjectCommand.php b/src/Composer/Command/CreateProjectCommand.php
index d7da384e4..bda43c5fa 100644
--- a/src/Composer/Command/CreateProjectCommand.php
+++ b/src/Composer/Command/CreateProjectCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/DependsCommand.php b/src/Composer/Command/DependsCommand.php
index 54fda17a5..0dbbb03f2 100644
--- a/src/Composer/Command/DependsCommand.php
+++ b/src/Composer/Command/DependsCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/DiagnoseCommand.php b/src/Composer/Command/DiagnoseCommand.php
index 8ed6ed0f4..93ef3c22a 100644
--- a/src/Composer/Command/DiagnoseCommand.php
+++ b/src/Composer/Command/DiagnoseCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/DumpAutoloadCommand.php b/src/Composer/Command/DumpAutoloadCommand.php
index 9eb81f699..9ec6abed0 100644
--- a/src/Composer/Command/DumpAutoloadCommand.php
+++ b/src/Composer/Command/DumpAutoloadCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/ExecCommand.php b/src/Composer/Command/ExecCommand.php
index ac3ed11ab..049f6b687 100644
--- a/src/Composer/Command/ExecCommand.php
+++ b/src/Composer/Command/ExecCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/FundCommand.php b/src/Composer/Command/FundCommand.php
index c6287dac9..057fea5d6 100644
--- a/src/Composer/Command/FundCommand.php
+++ b/src/Composer/Command/FundCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/GlobalCommand.php b/src/Composer/Command/GlobalCommand.php
index 0b5f442cc..3ec125427 100644
--- a/src/Composer/Command/GlobalCommand.php
+++ b/src/Composer/Command/GlobalCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/HomeCommand.php b/src/Composer/Command/HomeCommand.php
index 798d654df..dad4e3a75 100644
--- a/src/Composer/Command/HomeCommand.php
+++ b/src/Composer/Command/HomeCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/InitCommand.php b/src/Composer/Command/InitCommand.php
index 1d4dea29b..f923f6929 100644
--- a/src/Composer/Command/InitCommand.php
+++ b/src/Composer/Command/InitCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/InstallCommand.php b/src/Composer/Command/InstallCommand.php
index df1edf062..13b6ff400 100644
--- a/src/Composer/Command/InstallCommand.php
+++ b/src/Composer/Command/InstallCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/LicensesCommand.php b/src/Composer/Command/LicensesCommand.php
index b51292742..003538f3a 100644
--- a/src/Composer/Command/LicensesCommand.php
+++ b/src/Composer/Command/LicensesCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/OutdatedCommand.php b/src/Composer/Command/OutdatedCommand.php
index 332a4c64e..9bc2ee48b 100644
--- a/src/Composer/Command/OutdatedCommand.php
+++ b/src/Composer/Command/OutdatedCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/PackageDiscoveryTrait.php b/src/Composer/Command/PackageDiscoveryTrait.php
index a9685ae13..d6c13e79f 100644
--- a/src/Composer/Command/PackageDiscoveryTrait.php
+++ b/src/Composer/Command/PackageDiscoveryTrait.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/ProhibitsCommand.php b/src/Composer/Command/ProhibitsCommand.php
index 59165f4de..6da462084 100644
--- a/src/Composer/Command/ProhibitsCommand.php
+++ b/src/Composer/Command/ProhibitsCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/ReinstallCommand.php b/src/Composer/Command/ReinstallCommand.php
index 926ba9839..8150bfa22 100644
--- a/src/Composer/Command/ReinstallCommand.php
+++ b/src/Composer/Command/ReinstallCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/RemoveCommand.php b/src/Composer/Command/RemoveCommand.php
index fdda37df1..0ec091683 100644
--- a/src/Composer/Command/RemoveCommand.php
+++ b/src/Composer/Command/RemoveCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/RequireCommand.php b/src/Composer/Command/RequireCommand.php
index 5a65ccec9..3f4fa2965 100644
--- a/src/Composer/Command/RequireCommand.php
+++ b/src/Composer/Command/RequireCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/RunScriptCommand.php b/src/Composer/Command/RunScriptCommand.php
index fc66a9d04..94709f409 100644
--- a/src/Composer/Command/RunScriptCommand.php
+++ b/src/Composer/Command/RunScriptCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/ScriptAliasCommand.php b/src/Composer/Command/ScriptAliasCommand.php
index 793127f8c..4c34368ad 100644
--- a/src/Composer/Command/ScriptAliasCommand.php
+++ b/src/Composer/Command/ScriptAliasCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/SearchCommand.php b/src/Composer/Command/SearchCommand.php
index 496394a30..f701e40d9 100644
--- a/src/Composer/Command/SearchCommand.php
+++ b/src/Composer/Command/SearchCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/SelfUpdateCommand.php b/src/Composer/Command/SelfUpdateCommand.php
index f8f49405a..259abd5db 100644
--- a/src/Composer/Command/SelfUpdateCommand.php
+++ b/src/Composer/Command/SelfUpdateCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/ShowCommand.php b/src/Composer/Command/ShowCommand.php
index 8b11a8e33..b115a7f88 100644
--- a/src/Composer/Command/ShowCommand.php
+++ b/src/Composer/Command/ShowCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/StatusCommand.php b/src/Composer/Command/StatusCommand.php
index 58b6663a7..7721a6501 100644
--- a/src/Composer/Command/StatusCommand.php
+++ b/src/Composer/Command/StatusCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/SuggestsCommand.php b/src/Composer/Command/SuggestsCommand.php
index eae73a05c..23776abb5 100644
--- a/src/Composer/Command/SuggestsCommand.php
+++ b/src/Composer/Command/SuggestsCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/UpdateCommand.php b/src/Composer/Command/UpdateCommand.php
index 2250f225a..156ac35d9 100644
--- a/src/Composer/Command/UpdateCommand.php
+++ b/src/Composer/Command/UpdateCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Command/ValidateCommand.php b/src/Composer/Command/ValidateCommand.php
index e91008f5c..b1fac8d59 100644
--- a/src/Composer/Command/ValidateCommand.php
+++ b/src/Composer/Command/ValidateCommand.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Compiler.php b/src/Composer/Compiler.php
index 02e0ff022..d33f18f9f 100644
--- a/src/Composer/Compiler.php
+++ b/src/Composer/Compiler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Composer.php b/src/Composer/Composer.php
index a4b769ee2..93e8c0a6f 100644
--- a/src/Composer/Composer.php
+++ b/src/Composer/Composer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Config.php b/src/Composer/Config.php
index 18db2918e..fe3069f54 100644
--- a/src/Composer/Config.php
+++ b/src/Composer/Config.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Config/ConfigSourceInterface.php b/src/Composer/Config/ConfigSourceInterface.php
index 7cb590de6..f94ab630e 100644
--- a/src/Composer/Config/ConfigSourceInterface.php
+++ b/src/Composer/Config/ConfigSourceInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Config/JsonConfigSource.php b/src/Composer/Config/JsonConfigSource.php
index cb04bc6e9..4c031f5d8 100644
--- a/src/Composer/Config/JsonConfigSource.php
+++ b/src/Composer/Config/JsonConfigSource.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Console/Application.php b/src/Composer/Console/Application.php
index ccb60e6cf..b5166f9b8 100644
--- a/src/Composer/Console/Application.php
+++ b/src/Composer/Console/Application.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Console/GithubActionError.php b/src/Composer/Console/GithubActionError.php
index d73b55851..7489a9a38 100644
--- a/src/Composer/Console/GithubActionError.php
+++ b/src/Composer/Console/GithubActionError.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Console/HtmlOutputFormatter.php b/src/Composer/Console/HtmlOutputFormatter.php
index f95933a1b..04afda4fc 100644
--- a/src/Composer/Console/HtmlOutputFormatter.php
+++ b/src/Composer/Console/HtmlOutputFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Decisions.php b/src/Composer/DependencyResolver/Decisions.php
index f06a25a8b..fce11c269 100644
--- a/src/Composer/DependencyResolver/Decisions.php
+++ b/src/Composer/DependencyResolver/Decisions.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/DefaultPolicy.php b/src/Composer/DependencyResolver/DefaultPolicy.php
index e7610eb22..cdf13f0b0 100644
--- a/src/Composer/DependencyResolver/DefaultPolicy.php
+++ b/src/Composer/DependencyResolver/DefaultPolicy.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/GenericRule.php b/src/Composer/DependencyResolver/GenericRule.php
index ab010db0e..b18414666 100644
--- a/src/Composer/DependencyResolver/GenericRule.php
+++ b/src/Composer/DependencyResolver/GenericRule.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/LocalRepoTransaction.php b/src/Composer/DependencyResolver/LocalRepoTransaction.php
index 4a03816d7..06d987797 100644
--- a/src/Composer/DependencyResolver/LocalRepoTransaction.php
+++ b/src/Composer/DependencyResolver/LocalRepoTransaction.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/LockTransaction.php b/src/Composer/DependencyResolver/LockTransaction.php
index 3b3da5df2..e9bffab30 100644
--- a/src/Composer/DependencyResolver/LockTransaction.php
+++ b/src/Composer/DependencyResolver/LockTransaction.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/MultiConflictRule.php b/src/Composer/DependencyResolver/MultiConflictRule.php
index 104d578a8..63fe1e09e 100644
--- a/src/Composer/DependencyResolver/MultiConflictRule.php
+++ b/src/Composer/DependencyResolver/MultiConflictRule.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Operation/InstallOperation.php b/src/Composer/DependencyResolver/Operation/InstallOperation.php
index da31a52cc..7869402ab 100644
--- a/src/Composer/DependencyResolver/Operation/InstallOperation.php
+++ b/src/Composer/DependencyResolver/Operation/InstallOperation.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Operation/MarkAliasInstalledOperation.php b/src/Composer/DependencyResolver/Operation/MarkAliasInstalledOperation.php
index 8626813e2..84d48e3c4 100644
--- a/src/Composer/DependencyResolver/Operation/MarkAliasInstalledOperation.php
+++ b/src/Composer/DependencyResolver/Operation/MarkAliasInstalledOperation.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Operation/MarkAliasUninstalledOperation.php b/src/Composer/DependencyResolver/Operation/MarkAliasUninstalledOperation.php
index 1e858ef1e..b28e4942c 100644
--- a/src/Composer/DependencyResolver/Operation/MarkAliasUninstalledOperation.php
+++ b/src/Composer/DependencyResolver/Operation/MarkAliasUninstalledOperation.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Operation/OperationInterface.php b/src/Composer/DependencyResolver/Operation/OperationInterface.php
index 4cc70987d..45e6acd72 100644
--- a/src/Composer/DependencyResolver/Operation/OperationInterface.php
+++ b/src/Composer/DependencyResolver/Operation/OperationInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Operation/SolverOperation.php b/src/Composer/DependencyResolver/Operation/SolverOperation.php
index 094029af0..2eb9804ba 100644
--- a/src/Composer/DependencyResolver/Operation/SolverOperation.php
+++ b/src/Composer/DependencyResolver/Operation/SolverOperation.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Operation/UninstallOperation.php b/src/Composer/DependencyResolver/Operation/UninstallOperation.php
index 878691508..9caa3248c 100644
--- a/src/Composer/DependencyResolver/Operation/UninstallOperation.php
+++ b/src/Composer/DependencyResolver/Operation/UninstallOperation.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Operation/UpdateOperation.php b/src/Composer/DependencyResolver/Operation/UpdateOperation.php
index 728bb1511..f9f0fd4f5 100644
--- a/src/Composer/DependencyResolver/Operation/UpdateOperation.php
+++ b/src/Composer/DependencyResolver/Operation/UpdateOperation.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/PolicyInterface.php b/src/Composer/DependencyResolver/PolicyInterface.php
index 714041dc0..655ea7191 100644
--- a/src/Composer/DependencyResolver/PolicyInterface.php
+++ b/src/Composer/DependencyResolver/PolicyInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Pool.php b/src/Composer/DependencyResolver/Pool.php
index 1abbc6382..73a9052b8 100644
--- a/src/Composer/DependencyResolver/Pool.php
+++ b/src/Composer/DependencyResolver/Pool.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/PoolBuilder.php b/src/Composer/DependencyResolver/PoolBuilder.php
index 52c831dc5..676ebfefc 100644
--- a/src/Composer/DependencyResolver/PoolBuilder.php
+++ b/src/Composer/DependencyResolver/PoolBuilder.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/PoolOptimizer.php b/src/Composer/DependencyResolver/PoolOptimizer.php
index 6d9b1dd12..1304a5941 100644
--- a/src/Composer/DependencyResolver/PoolOptimizer.php
+++ b/src/Composer/DependencyResolver/PoolOptimizer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Problem.php b/src/Composer/DependencyResolver/Problem.php
index 44ad896a9..06a2378ab 100644
--- a/src/Composer/DependencyResolver/Problem.php
+++ b/src/Composer/DependencyResolver/Problem.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Request.php b/src/Composer/DependencyResolver/Request.php
index d7cde0793..e08ae06c7 100644
--- a/src/Composer/DependencyResolver/Request.php
+++ b/src/Composer/DependencyResolver/Request.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Rule.php b/src/Composer/DependencyResolver/Rule.php
index 55e75e624..8909f67fe 100644
--- a/src/Composer/DependencyResolver/Rule.php
+++ b/src/Composer/DependencyResolver/Rule.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Rule2Literals.php b/src/Composer/DependencyResolver/Rule2Literals.php
index 9545686c8..bfac6dbfe 100644
--- a/src/Composer/DependencyResolver/Rule2Literals.php
+++ b/src/Composer/DependencyResolver/Rule2Literals.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/RuleSet.php b/src/Composer/DependencyResolver/RuleSet.php
index 9d856c4b6..69159fd79 100644
--- a/src/Composer/DependencyResolver/RuleSet.php
+++ b/src/Composer/DependencyResolver/RuleSet.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/RuleSetGenerator.php b/src/Composer/DependencyResolver/RuleSetGenerator.php
index d170db1e3..c91141d54 100644
--- a/src/Composer/DependencyResolver/RuleSetGenerator.php
+++ b/src/Composer/DependencyResolver/RuleSetGenerator.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/RuleSetIterator.php b/src/Composer/DependencyResolver/RuleSetIterator.php
index e7afb55d3..3d30c5d7e 100644
--- a/src/Composer/DependencyResolver/RuleSetIterator.php
+++ b/src/Composer/DependencyResolver/RuleSetIterator.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/RuleWatchChain.php b/src/Composer/DependencyResolver/RuleWatchChain.php
index f6bab3547..f9b90d4a9 100644
--- a/src/Composer/DependencyResolver/RuleWatchChain.php
+++ b/src/Composer/DependencyResolver/RuleWatchChain.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/RuleWatchGraph.php b/src/Composer/DependencyResolver/RuleWatchGraph.php
index 0b74a9888..2fea3c43d 100644
--- a/src/Composer/DependencyResolver/RuleWatchGraph.php
+++ b/src/Composer/DependencyResolver/RuleWatchGraph.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/RuleWatchNode.php b/src/Composer/DependencyResolver/RuleWatchNode.php
index d1e027cd2..54e4283c0 100644
--- a/src/Composer/DependencyResolver/RuleWatchNode.php
+++ b/src/Composer/DependencyResolver/RuleWatchNode.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Solver.php b/src/Composer/DependencyResolver/Solver.php
index 0a0720398..2c416a95e 100644
--- a/src/Composer/DependencyResolver/Solver.php
+++ b/src/Composer/DependencyResolver/Solver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/SolverBugException.php b/src/Composer/DependencyResolver/SolverBugException.php
index 0a8d453ee..394958a8f 100644
--- a/src/Composer/DependencyResolver/SolverBugException.php
+++ b/src/Composer/DependencyResolver/SolverBugException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/SolverProblemsException.php b/src/Composer/DependencyResolver/SolverProblemsException.php
index 57dfcf000..ea8c86af5 100644
--- a/src/Composer/DependencyResolver/SolverProblemsException.php
+++ b/src/Composer/DependencyResolver/SolverProblemsException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/DependencyResolver/Transaction.php b/src/Composer/DependencyResolver/Transaction.php
index 184855e73..c9db082df 100644
--- a/src/Composer/DependencyResolver/Transaction.php
+++ b/src/Composer/DependencyResolver/Transaction.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/ArchiveDownloader.php b/src/Composer/Downloader/ArchiveDownloader.php
index 449593a6b..50c00ac24 100644
--- a/src/Composer/Downloader/ArchiveDownloader.php
+++ b/src/Composer/Downloader/ArchiveDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/ChangeReportInterface.php b/src/Composer/Downloader/ChangeReportInterface.php
index a41cce893..857a7f09e 100644
--- a/src/Composer/Downloader/ChangeReportInterface.php
+++ b/src/Composer/Downloader/ChangeReportInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/DownloadManager.php b/src/Composer/Downloader/DownloadManager.php
index f34a73d37..2aa4c7b24 100644
--- a/src/Composer/Downloader/DownloadManager.php
+++ b/src/Composer/Downloader/DownloadManager.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/DownloaderInterface.php b/src/Composer/Downloader/DownloaderInterface.php
index 0b540d4b6..5ed8cfc68 100644
--- a/src/Composer/Downloader/DownloaderInterface.php
+++ b/src/Composer/Downloader/DownloaderInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/DvcsDownloaderInterface.php b/src/Composer/Downloader/DvcsDownloaderInterface.php
index 45c9b86c5..879aab2ed 100644
--- a/src/Composer/Downloader/DvcsDownloaderInterface.php
+++ b/src/Composer/Downloader/DvcsDownloaderInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/FileDownloader.php b/src/Composer/Downloader/FileDownloader.php
index c1858d9b8..738a386ae 100644
--- a/src/Composer/Downloader/FileDownloader.php
+++ b/src/Composer/Downloader/FileDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/FilesystemException.php b/src/Composer/Downloader/FilesystemException.php
index f9d4e6fbe..5aff2f089 100644
--- a/src/Composer/Downloader/FilesystemException.php
+++ b/src/Composer/Downloader/FilesystemException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/FossilDownloader.php b/src/Composer/Downloader/FossilDownloader.php
index 13bd3d25b..d1ae129c3 100644
--- a/src/Composer/Downloader/FossilDownloader.php
+++ b/src/Composer/Downloader/FossilDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/GitDownloader.php b/src/Composer/Downloader/GitDownloader.php
index a842a6ea3..89a4debab 100644
--- a/src/Composer/Downloader/GitDownloader.php
+++ b/src/Composer/Downloader/GitDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/GzipDownloader.php b/src/Composer/Downloader/GzipDownloader.php
index 8949037ec..60ab50549 100644
--- a/src/Composer/Downloader/GzipDownloader.php
+++ b/src/Composer/Downloader/GzipDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/HgDownloader.php b/src/Composer/Downloader/HgDownloader.php
index 0537103b1..c32375c97 100644
--- a/src/Composer/Downloader/HgDownloader.php
+++ b/src/Composer/Downloader/HgDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/MaxFileSizeExceededException.php b/src/Composer/Downloader/MaxFileSizeExceededException.php
index b7adad1b6..e57e7affd 100644
--- a/src/Composer/Downloader/MaxFileSizeExceededException.php
+++ b/src/Composer/Downloader/MaxFileSizeExceededException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/PathDownloader.php b/src/Composer/Downloader/PathDownloader.php
index 0cf5d3edf..7749d1fd7 100644
--- a/src/Composer/Downloader/PathDownloader.php
+++ b/src/Composer/Downloader/PathDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/PerforceDownloader.php b/src/Composer/Downloader/PerforceDownloader.php
index 559d6ba4a..785f2fb6a 100644
--- a/src/Composer/Downloader/PerforceDownloader.php
+++ b/src/Composer/Downloader/PerforceDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/PharDownloader.php b/src/Composer/Downloader/PharDownloader.php
index 76517fcd7..b70d8e81d 100644
--- a/src/Composer/Downloader/PharDownloader.php
+++ b/src/Composer/Downloader/PharDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/RarDownloader.php b/src/Composer/Downloader/RarDownloader.php
index ef697d797..8411f02a2 100644
--- a/src/Composer/Downloader/RarDownloader.php
+++ b/src/Composer/Downloader/RarDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/SvnDownloader.php b/src/Composer/Downloader/SvnDownloader.php
index 056add89c..7e532f444 100644
--- a/src/Composer/Downloader/SvnDownloader.php
+++ b/src/Composer/Downloader/SvnDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/TarDownloader.php b/src/Composer/Downloader/TarDownloader.php
index 92998aac6..829166112 100644
--- a/src/Composer/Downloader/TarDownloader.php
+++ b/src/Composer/Downloader/TarDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/TransportException.php b/src/Composer/Downloader/TransportException.php
index 89719becf..3a9209be4 100644
--- a/src/Composer/Downloader/TransportException.php
+++ b/src/Composer/Downloader/TransportException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/VcsCapableDownloaderInterface.php b/src/Composer/Downloader/VcsCapableDownloaderInterface.php
index 38d12c689..879170276 100644
--- a/src/Composer/Downloader/VcsCapableDownloaderInterface.php
+++ b/src/Composer/Downloader/VcsCapableDownloaderInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/VcsDownloader.php b/src/Composer/Downloader/VcsDownloader.php
index 12f5140f5..240eb8930 100644
--- a/src/Composer/Downloader/VcsDownloader.php
+++ b/src/Composer/Downloader/VcsDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/XzDownloader.php b/src/Composer/Downloader/XzDownloader.php
index 50325603e..e476f9820 100644
--- a/src/Composer/Downloader/XzDownloader.php
+++ b/src/Composer/Downloader/XzDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Downloader/ZipDownloader.php b/src/Composer/Downloader/ZipDownloader.php
index e532bdcdd..7fed754f2 100644
--- a/src/Composer/Downloader/ZipDownloader.php
+++ b/src/Composer/Downloader/ZipDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/EventDispatcher/Event.php b/src/Composer/EventDispatcher/Event.php
index a3f2294ef..06bd00655 100644
--- a/src/Composer/EventDispatcher/Event.php
+++ b/src/Composer/EventDispatcher/Event.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/EventDispatcher/EventDispatcher.php b/src/Composer/EventDispatcher/EventDispatcher.php
index d0cd437bd..118c75f5b 100644
--- a/src/Composer/EventDispatcher/EventDispatcher.php
+++ b/src/Composer/EventDispatcher/EventDispatcher.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/EventDispatcher/EventSubscriberInterface.php b/src/Composer/EventDispatcher/EventSubscriberInterface.php
index 4de66c80b..fe0c5bd02 100644
--- a/src/Composer/EventDispatcher/EventSubscriberInterface.php
+++ b/src/Composer/EventDispatcher/EventSubscriberInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/EventDispatcher/ScriptExecutionException.php b/src/Composer/EventDispatcher/ScriptExecutionException.php
index 2b12ff68d..3b05a8831 100644
--- a/src/Composer/EventDispatcher/ScriptExecutionException.php
+++ b/src/Composer/EventDispatcher/ScriptExecutionException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Exception/IrrecoverableDownloadException.php b/src/Composer/Exception/IrrecoverableDownloadException.php
index 72a833c72..a442786ae 100644
--- a/src/Composer/Exception/IrrecoverableDownloadException.php
+++ b/src/Composer/Exception/IrrecoverableDownloadException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Exception/NoSslException.php b/src/Composer/Exception/NoSslException.php
index 55c81fea9..4696dd3a5 100644
--- a/src/Composer/Exception/NoSslException.php
+++ b/src/Composer/Exception/NoSslException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Factory.php b/src/Composer/Factory.php
index c6980057c..697a742cb 100644
--- a/src/Composer/Factory.php
+++ b/src/Composer/Factory.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilter.php b/src/Composer/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilter.php
index db779c3c1..6076c0b04 100644
--- a/src/Composer/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilter.php
+++ b/src/Composer/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilter.php b/src/Composer/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilter.php
index 5a146bfe3..7e2e7e926 100644
--- a/src/Composer/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilter.php
+++ b/src/Composer/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilter.php b/src/Composer/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilter.php
index 882275b41..0e2651214 100644
--- a/src/Composer/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilter.php
+++ b/src/Composer/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactory.php b/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactory.php
index 302bdd915..b735d13ae 100644
--- a/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactory.php
+++ b/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactory.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterInterface.php b/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterInterface.php
index de0fc234a..9a80837a2 100644
--- a/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterInterface.php
+++ b/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/IO/BaseIO.php b/src/Composer/IO/BaseIO.php
index 807e0ee3a..d7247e411 100644
--- a/src/Composer/IO/BaseIO.php
+++ b/src/Composer/IO/BaseIO.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/IO/BufferIO.php b/src/Composer/IO/BufferIO.php
index 0e9b44a25..ecbb4a303 100644
--- a/src/Composer/IO/BufferIO.php
+++ b/src/Composer/IO/BufferIO.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/IO/ConsoleIO.php b/src/Composer/IO/ConsoleIO.php
index b63baca77..971d52736 100644
--- a/src/Composer/IO/ConsoleIO.php
+++ b/src/Composer/IO/ConsoleIO.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/IO/IOInterface.php b/src/Composer/IO/IOInterface.php
index ba987cc8a..a1048be8e 100644
--- a/src/Composer/IO/IOInterface.php
+++ b/src/Composer/IO/IOInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/IO/NullIO.php b/src/Composer/IO/NullIO.php
index 88c4a8c74..fd73feec9 100644
--- a/src/Composer/IO/NullIO.php
+++ b/src/Composer/IO/NullIO.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer.php b/src/Composer/Installer.php
index 162918a5e..5153a81dc 100644
--- a/src/Composer/Installer.php
+++ b/src/Composer/Installer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/BinaryInstaller.php b/src/Composer/Installer/BinaryInstaller.php
index 05f3c0b34..fc1d5d7a1 100644
--- a/src/Composer/Installer/BinaryInstaller.php
+++ b/src/Composer/Installer/BinaryInstaller.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/BinaryPresenceInterface.php b/src/Composer/Installer/BinaryPresenceInterface.php
index 61907f778..d920b0ecc 100644
--- a/src/Composer/Installer/BinaryPresenceInterface.php
+++ b/src/Composer/Installer/BinaryPresenceInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/InstallationManager.php b/src/Composer/Installer/InstallationManager.php
index 8200080b3..261dbb503 100644
--- a/src/Composer/Installer/InstallationManager.php
+++ b/src/Composer/Installer/InstallationManager.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/InstallerEvent.php b/src/Composer/Installer/InstallerEvent.php
index cafd0dc1b..a87ce66a0 100644
--- a/src/Composer/Installer/InstallerEvent.php
+++ b/src/Composer/Installer/InstallerEvent.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/InstallerEvents.php b/src/Composer/Installer/InstallerEvents.php
index d536b459c..fc3da51ee 100644
--- a/src/Composer/Installer/InstallerEvents.php
+++ b/src/Composer/Installer/InstallerEvents.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/InstallerInterface.php b/src/Composer/Installer/InstallerInterface.php
index 8ddbed4e6..a236e07ce 100644
--- a/src/Composer/Installer/InstallerInterface.php
+++ b/src/Composer/Installer/InstallerInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/LibraryInstaller.php b/src/Composer/Installer/LibraryInstaller.php
index 7d88a6d9b..504380913 100644
--- a/src/Composer/Installer/LibraryInstaller.php
+++ b/src/Composer/Installer/LibraryInstaller.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/MetapackageInstaller.php b/src/Composer/Installer/MetapackageInstaller.php
index ccc71c3fa..21ffaa505 100644
--- a/src/Composer/Installer/MetapackageInstaller.php
+++ b/src/Composer/Installer/MetapackageInstaller.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/NoopInstaller.php b/src/Composer/Installer/NoopInstaller.php
index d1aa1fa18..d31338854 100644
--- a/src/Composer/Installer/NoopInstaller.php
+++ b/src/Composer/Installer/NoopInstaller.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/PackageEvent.php b/src/Composer/Installer/PackageEvent.php
index 55029fb93..e16ca694c 100644
--- a/src/Composer/Installer/PackageEvent.php
+++ b/src/Composer/Installer/PackageEvent.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/PackageEvents.php b/src/Composer/Installer/PackageEvents.php
index 852da58ff..04f51a91f 100644
--- a/src/Composer/Installer/PackageEvents.php
+++ b/src/Composer/Installer/PackageEvents.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/PluginInstaller.php b/src/Composer/Installer/PluginInstaller.php
index 2dded4eac..48c403d85 100644
--- a/src/Composer/Installer/PluginInstaller.php
+++ b/src/Composer/Installer/PluginInstaller.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/ProjectInstaller.php b/src/Composer/Installer/ProjectInstaller.php
index 60c499f95..d981680ab 100644
--- a/src/Composer/Installer/ProjectInstaller.php
+++ b/src/Composer/Installer/ProjectInstaller.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Installer/SuggestedPackagesReporter.php b/src/Composer/Installer/SuggestedPackagesReporter.php
index f2cfafebd..315afea5b 100644
--- a/src/Composer/Installer/SuggestedPackagesReporter.php
+++ b/src/Composer/Installer/SuggestedPackagesReporter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Json/JsonFile.php b/src/Composer/Json/JsonFile.php
index fb6485b43..987de5cbb 100644
--- a/src/Composer/Json/JsonFile.php
+++ b/src/Composer/Json/JsonFile.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Json/JsonFormatter.php b/src/Composer/Json/JsonFormatter.php
index de6882689..8ea6f7509 100644
--- a/src/Composer/Json/JsonFormatter.php
+++ b/src/Composer/Json/JsonFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Json/JsonManipulator.php b/src/Composer/Json/JsonManipulator.php
index 4a8781c64..96a188d16 100644
--- a/src/Composer/Json/JsonManipulator.php
+++ b/src/Composer/Json/JsonManipulator.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Json/JsonValidationException.php b/src/Composer/Json/JsonValidationException.php
index 1187b2f99..783d471d1 100644
--- a/src/Composer/Json/JsonValidationException.php
+++ b/src/Composer/Json/JsonValidationException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/AliasPackage.php b/src/Composer/Package/AliasPackage.php
index 332c1fe05..2a7663d2a 100644
--- a/src/Composer/Package/AliasPackage.php
+++ b/src/Composer/Package/AliasPackage.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Archiver/ArchivableFilesFilter.php b/src/Composer/Package/Archiver/ArchivableFilesFilter.php
index 8af84271d..b454dca4d 100644
--- a/src/Composer/Package/Archiver/ArchivableFilesFilter.php
+++ b/src/Composer/Package/Archiver/ArchivableFilesFilter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Archiver/ArchivableFilesFinder.php b/src/Composer/Package/Archiver/ArchivableFilesFinder.php
index 9a53b719e..a4382c029 100644
--- a/src/Composer/Package/Archiver/ArchivableFilesFinder.php
+++ b/src/Composer/Package/Archiver/ArchivableFilesFinder.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Archiver/ArchiveManager.php b/src/Composer/Package/Archiver/ArchiveManager.php
index c7f5def61..75d010a1e 100644
--- a/src/Composer/Package/Archiver/ArchiveManager.php
+++ b/src/Composer/Package/Archiver/ArchiveManager.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Archiver/ArchiverInterface.php b/src/Composer/Package/Archiver/ArchiverInterface.php
index f18e8b45f..f19b2c285 100644
--- a/src/Composer/Package/Archiver/ArchiverInterface.php
+++ b/src/Composer/Package/Archiver/ArchiverInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Archiver/BaseExcludeFilter.php b/src/Composer/Package/Archiver/BaseExcludeFilter.php
index 21a8db5d8..13b215199 100644
--- a/src/Composer/Package/Archiver/BaseExcludeFilter.php
+++ b/src/Composer/Package/Archiver/BaseExcludeFilter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Archiver/ComposerExcludeFilter.php b/src/Composer/Package/Archiver/ComposerExcludeFilter.php
index 07d1e162d..9806b77c2 100644
--- a/src/Composer/Package/Archiver/ComposerExcludeFilter.php
+++ b/src/Composer/Package/Archiver/ComposerExcludeFilter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Archiver/GitExcludeFilter.php b/src/Composer/Package/Archiver/GitExcludeFilter.php
index d81dc7693..2d41e9c08 100644
--- a/src/Composer/Package/Archiver/GitExcludeFilter.php
+++ b/src/Composer/Package/Archiver/GitExcludeFilter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Archiver/PharArchiver.php b/src/Composer/Package/Archiver/PharArchiver.php
index f0d3abaf5..d7ecf9dbe 100644
--- a/src/Composer/Package/Archiver/PharArchiver.php
+++ b/src/Composer/Package/Archiver/PharArchiver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Archiver/ZipArchiver.php b/src/Composer/Package/Archiver/ZipArchiver.php
index 8c7a4e59c..59687a2b2 100644
--- a/src/Composer/Package/Archiver/ZipArchiver.php
+++ b/src/Composer/Package/Archiver/ZipArchiver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/BasePackage.php b/src/Composer/Package/BasePackage.php
index 3ab352f6b..b815aec53 100644
--- a/src/Composer/Package/BasePackage.php
+++ b/src/Composer/Package/BasePackage.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Comparer/Comparer.php b/src/Composer/Package/Comparer/Comparer.php
index d9d5a20f1..a2dd890bb 100644
--- a/src/Composer/Package/Comparer/Comparer.php
+++ b/src/Composer/Package/Comparer/Comparer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/CompleteAliasPackage.php b/src/Composer/Package/CompleteAliasPackage.php
index f69ad6298..78106fa3c 100644
--- a/src/Composer/Package/CompleteAliasPackage.php
+++ b/src/Composer/Package/CompleteAliasPackage.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/CompletePackage.php b/src/Composer/Package/CompletePackage.php
index 666f3b0c7..fc706cfe9 100644
--- a/src/Composer/Package/CompletePackage.php
+++ b/src/Composer/Package/CompletePackage.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/CompletePackageInterface.php b/src/Composer/Package/CompletePackageInterface.php
index 35db9e3cb..c6198dfe6 100644
--- a/src/Composer/Package/CompletePackageInterface.php
+++ b/src/Composer/Package/CompletePackageInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Dumper/ArrayDumper.php b/src/Composer/Package/Dumper/ArrayDumper.php
index e5ca23985..d150504e6 100644
--- a/src/Composer/Package/Dumper/ArrayDumper.php
+++ b/src/Composer/Package/Dumper/ArrayDumper.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Link.php b/src/Composer/Package/Link.php
index 1430cd800..59bfb993f 100644
--- a/src/Composer/Package/Link.php
+++ b/src/Composer/Package/Link.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Loader/ArrayLoader.php b/src/Composer/Package/Loader/ArrayLoader.php
index 5184eb01f..abebb4163 100644
--- a/src/Composer/Package/Loader/ArrayLoader.php
+++ b/src/Composer/Package/Loader/ArrayLoader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Loader/InvalidPackageException.php b/src/Composer/Package/Loader/InvalidPackageException.php
index 80c713544..d021564ad 100644
--- a/src/Composer/Package/Loader/InvalidPackageException.php
+++ b/src/Composer/Package/Loader/InvalidPackageException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Loader/JsonLoader.php b/src/Composer/Package/Loader/JsonLoader.php
index 4bfeaff8b..3ad5787b1 100644
--- a/src/Composer/Package/Loader/JsonLoader.php
+++ b/src/Composer/Package/Loader/JsonLoader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Loader/LoaderInterface.php b/src/Composer/Package/Loader/LoaderInterface.php
index be2e47042..cbf1b4c34 100644
--- a/src/Composer/Package/Loader/LoaderInterface.php
+++ b/src/Composer/Package/Loader/LoaderInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Loader/RootPackageLoader.php b/src/Composer/Package/Loader/RootPackageLoader.php
index 89eb27636..c4c345065 100644
--- a/src/Composer/Package/Loader/RootPackageLoader.php
+++ b/src/Composer/Package/Loader/RootPackageLoader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Loader/ValidatingArrayLoader.php b/src/Composer/Package/Loader/ValidatingArrayLoader.php
index 9fb4a19cd..cce97be79 100644
--- a/src/Composer/Package/Loader/ValidatingArrayLoader.php
+++ b/src/Composer/Package/Loader/ValidatingArrayLoader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Locker.php b/src/Composer/Package/Locker.php
index 6dc77cf5b..bb780bb54 100644
--- a/src/Composer/Package/Locker.php
+++ b/src/Composer/Package/Locker.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Package.php b/src/Composer/Package/Package.php
index 90dc0688f..e004ca677 100644
--- a/src/Composer/Package/Package.php
+++ b/src/Composer/Package/Package.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/PackageInterface.php b/src/Composer/Package/PackageInterface.php
index e666e7139..e31abef29 100644
--- a/src/Composer/Package/PackageInterface.php
+++ b/src/Composer/Package/PackageInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/RootAliasPackage.php b/src/Composer/Package/RootAliasPackage.php
index 7c780189f..eaa71fd11 100644
--- a/src/Composer/Package/RootAliasPackage.php
+++ b/src/Composer/Package/RootAliasPackage.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/RootPackage.php b/src/Composer/Package/RootPackage.php
index a0b7ec950..bf227eb44 100644
--- a/src/Composer/Package/RootPackage.php
+++ b/src/Composer/Package/RootPackage.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/RootPackageInterface.php b/src/Composer/Package/RootPackageInterface.php
index 9e74e4ddc..ad1828570 100644
--- a/src/Composer/Package/RootPackageInterface.php
+++ b/src/Composer/Package/RootPackageInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Version/StabilityFilter.php b/src/Composer/Package/Version/StabilityFilter.php
index 4280d7499..172901d44 100644
--- a/src/Composer/Package/Version/StabilityFilter.php
+++ b/src/Composer/Package/Version/StabilityFilter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Version/VersionGuesser.php b/src/Composer/Package/Version/VersionGuesser.php
index 30961de4b..7e7a0cae1 100644
--- a/src/Composer/Package/Version/VersionGuesser.php
+++ b/src/Composer/Package/Version/VersionGuesser.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Version/VersionParser.php b/src/Composer/Package/Version/VersionParser.php
index 6c0345999..ca0a11773 100644
--- a/src/Composer/Package/Version/VersionParser.php
+++ b/src/Composer/Package/Version/VersionParser.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Package/Version/VersionSelector.php b/src/Composer/Package/Version/VersionSelector.php
index cc8fe2382..f1cfeafc5 100644
--- a/src/Composer/Package/Version/VersionSelector.php
+++ b/src/Composer/Package/Version/VersionSelector.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/PartialComposer.php b/src/Composer/PartialComposer.php
index 891175066..b5c859ae9 100644
--- a/src/Composer/PartialComposer.php
+++ b/src/Composer/PartialComposer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Platform/HhvmDetector.php b/src/Composer/Platform/HhvmDetector.php
index 2785d26c4..f6c5829b6 100644
--- a/src/Composer/Platform/HhvmDetector.php
+++ b/src/Composer/Platform/HhvmDetector.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Platform/Runtime.php b/src/Composer/Platform/Runtime.php
index 6ccdbf546..725c3dbbc 100644
--- a/src/Composer/Platform/Runtime.php
+++ b/src/Composer/Platform/Runtime.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Platform/Version.php b/src/Composer/Platform/Version.php
index 0731a1cec..1ad22c3ed 100644
--- a/src/Composer/Platform/Version.php
+++ b/src/Composer/Platform/Version.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/Capability/Capability.php b/src/Composer/Plugin/Capability/Capability.php
index b12410608..b2237b44b 100644
--- a/src/Composer/Plugin/Capability/Capability.php
+++ b/src/Composer/Plugin/Capability/Capability.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/Capability/CommandProvider.php b/src/Composer/Plugin/Capability/CommandProvider.php
index 0f94bf37c..884b9554d 100644
--- a/src/Composer/Plugin/Capability/CommandProvider.php
+++ b/src/Composer/Plugin/Capability/CommandProvider.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/Capable.php b/src/Composer/Plugin/Capable.php
index 48ae42250..9a45833c8 100644
--- a/src/Composer/Plugin/Capable.php
+++ b/src/Composer/Plugin/Capable.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/CommandEvent.php b/src/Composer/Plugin/CommandEvent.php
index 03d621eb5..d861671c0 100644
--- a/src/Composer/Plugin/CommandEvent.php
+++ b/src/Composer/Plugin/CommandEvent.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/PluginEvents.php b/src/Composer/Plugin/PluginEvents.php
index c2e58d510..5a82018c0 100644
--- a/src/Composer/Plugin/PluginEvents.php
+++ b/src/Composer/Plugin/PluginEvents.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/PluginInterface.php b/src/Composer/Plugin/PluginInterface.php
index ae5139a84..e5982fdf5 100644
--- a/src/Composer/Plugin/PluginInterface.php
+++ b/src/Composer/Plugin/PluginInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/PluginManager.php b/src/Composer/Plugin/PluginManager.php
index 537f3b6ec..87a2faf23 100644
--- a/src/Composer/Plugin/PluginManager.php
+++ b/src/Composer/Plugin/PluginManager.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/PostFileDownloadEvent.php b/src/Composer/Plugin/PostFileDownloadEvent.php
index 5fecd9b01..a19a9e38e 100644
--- a/src/Composer/Plugin/PostFileDownloadEvent.php
+++ b/src/Composer/Plugin/PostFileDownloadEvent.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/PreCommandRunEvent.php b/src/Composer/Plugin/PreCommandRunEvent.php
index bb0d9a9a4..4afd03a33 100644
--- a/src/Composer/Plugin/PreCommandRunEvent.php
+++ b/src/Composer/Plugin/PreCommandRunEvent.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/PreFileDownloadEvent.php b/src/Composer/Plugin/PreFileDownloadEvent.php
index 762952840..53fd54f4a 100644
--- a/src/Composer/Plugin/PreFileDownloadEvent.php
+++ b/src/Composer/Plugin/PreFileDownloadEvent.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Plugin/PrePoolCreateEvent.php b/src/Composer/Plugin/PrePoolCreateEvent.php
index c647378ac..dee00e4d5 100644
--- a/src/Composer/Plugin/PrePoolCreateEvent.php
+++ b/src/Composer/Plugin/PrePoolCreateEvent.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Question/StrictConfirmationQuestion.php b/src/Composer/Question/StrictConfirmationQuestion.php
index c656a6126..b815675c6 100644
--- a/src/Composer/Question/StrictConfirmationQuestion.php
+++ b/src/Composer/Question/StrictConfirmationQuestion.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/ArrayRepository.php b/src/Composer/Repository/ArrayRepository.php
index d1a10e3ea..0f8e101bd 100644
--- a/src/Composer/Repository/ArrayRepository.php
+++ b/src/Composer/Repository/ArrayRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/ArtifactRepository.php b/src/Composer/Repository/ArtifactRepository.php
index 0739ba1bc..e796739d0 100644
--- a/src/Composer/Repository/ArtifactRepository.php
+++ b/src/Composer/Repository/ArtifactRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/ComposerRepository.php b/src/Composer/Repository/ComposerRepository.php
index 22f8c5548..72005682b 100644
--- a/src/Composer/Repository/ComposerRepository.php
+++ b/src/Composer/Repository/ComposerRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/CompositeRepository.php b/src/Composer/Repository/CompositeRepository.php
index 3d31aa1de..d10815c35 100644
--- a/src/Composer/Repository/CompositeRepository.php
+++ b/src/Composer/Repository/CompositeRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/ConfigurableRepositoryInterface.php b/src/Composer/Repository/ConfigurableRepositoryInterface.php
index 46a535830..a56540f03 100644
--- a/src/Composer/Repository/ConfigurableRepositoryInterface.php
+++ b/src/Composer/Repository/ConfigurableRepositoryInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/FilesystemRepository.php b/src/Composer/Repository/FilesystemRepository.php
index 81745ed7b..cd677c18f 100644
--- a/src/Composer/Repository/FilesystemRepository.php
+++ b/src/Composer/Repository/FilesystemRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/FilterRepository.php b/src/Composer/Repository/FilterRepository.php
index db678a3f3..5072e1696 100644
--- a/src/Composer/Repository/FilterRepository.php
+++ b/src/Composer/Repository/FilterRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/InstalledArrayRepository.php b/src/Composer/Repository/InstalledArrayRepository.php
index d046a9973..971276fbd 100644
--- a/src/Composer/Repository/InstalledArrayRepository.php
+++ b/src/Composer/Repository/InstalledArrayRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/InstalledFilesystemRepository.php b/src/Composer/Repository/InstalledFilesystemRepository.php
index ac8bef79a..393a38422 100644
--- a/src/Composer/Repository/InstalledFilesystemRepository.php
+++ b/src/Composer/Repository/InstalledFilesystemRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/InstalledRepository.php b/src/Composer/Repository/InstalledRepository.php
index c31573721..2c3231a9d 100644
--- a/src/Composer/Repository/InstalledRepository.php
+++ b/src/Composer/Repository/InstalledRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/InstalledRepositoryInterface.php b/src/Composer/Repository/InstalledRepositoryInterface.php
index a25d7369e..3b89d1da2 100644
--- a/src/Composer/Repository/InstalledRepositoryInterface.php
+++ b/src/Composer/Repository/InstalledRepositoryInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/InvalidRepositoryException.php b/src/Composer/Repository/InvalidRepositoryException.php
index 061a5048b..9dbd6f0de 100644
--- a/src/Composer/Repository/InvalidRepositoryException.php
+++ b/src/Composer/Repository/InvalidRepositoryException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/LockArrayRepository.php b/src/Composer/Repository/LockArrayRepository.php
index ddccdd0b1..2203525c3 100644
--- a/src/Composer/Repository/LockArrayRepository.php
+++ b/src/Composer/Repository/LockArrayRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/PackageRepository.php b/src/Composer/Repository/PackageRepository.php
index f0ed385ee..4fbadccef 100644
--- a/src/Composer/Repository/PackageRepository.php
+++ b/src/Composer/Repository/PackageRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/PathRepository.php b/src/Composer/Repository/PathRepository.php
index dcb9c82d5..5241e0015 100644
--- a/src/Composer/Repository/PathRepository.php
+++ b/src/Composer/Repository/PathRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/PearRepository.php b/src/Composer/Repository/PearRepository.php
index 0998f302d..facc41787 100644
--- a/src/Composer/Repository/PearRepository.php
+++ b/src/Composer/Repository/PearRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/PlatformRepository.php b/src/Composer/Repository/PlatformRepository.php
index 6d8afe4a1..d31e0ede2 100644
--- a/src/Composer/Repository/PlatformRepository.php
+++ b/src/Composer/Repository/PlatformRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/RepositoryFactory.php b/src/Composer/Repository/RepositoryFactory.php
index 25e86aa52..b31f77530 100644
--- a/src/Composer/Repository/RepositoryFactory.php
+++ b/src/Composer/Repository/RepositoryFactory.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/RepositoryInterface.php b/src/Composer/Repository/RepositoryInterface.php
index 129a09498..9b612f610 100644
--- a/src/Composer/Repository/RepositoryInterface.php
+++ b/src/Composer/Repository/RepositoryInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/RepositoryManager.php b/src/Composer/Repository/RepositoryManager.php
index 0f119931e..c09fe1421 100644
--- a/src/Composer/Repository/RepositoryManager.php
+++ b/src/Composer/Repository/RepositoryManager.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/RepositorySecurityException.php b/src/Composer/Repository/RepositorySecurityException.php
index b115d9cbe..c4323145c 100644
--- a/src/Composer/Repository/RepositorySecurityException.php
+++ b/src/Composer/Repository/RepositorySecurityException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/RepositorySet.php b/src/Composer/Repository/RepositorySet.php
index c0e39fd5f..e3ad49dfe 100644
--- a/src/Composer/Repository/RepositorySet.php
+++ b/src/Composer/Repository/RepositorySet.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/RootPackageRepository.php b/src/Composer/Repository/RootPackageRepository.php
index e1aa37443..0cce7ec53 100644
--- a/src/Composer/Repository/RootPackageRepository.php
+++ b/src/Composer/Repository/RootPackageRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/Vcs/FossilDriver.php b/src/Composer/Repository/Vcs/FossilDriver.php
index 1fb0fb36b..b8b342905 100644
--- a/src/Composer/Repository/Vcs/FossilDriver.php
+++ b/src/Composer/Repository/Vcs/FossilDriver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/Vcs/GitBitbucketDriver.php b/src/Composer/Repository/Vcs/GitBitbucketDriver.php
index 1e045c3e9..33bee56eb 100644
--- a/src/Composer/Repository/Vcs/GitBitbucketDriver.php
+++ b/src/Composer/Repository/Vcs/GitBitbucketDriver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/Vcs/GitDriver.php b/src/Composer/Repository/Vcs/GitDriver.php
index 978db48ec..182d2816b 100644
--- a/src/Composer/Repository/Vcs/GitDriver.php
+++ b/src/Composer/Repository/Vcs/GitDriver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/Vcs/GitHubDriver.php b/src/Composer/Repository/Vcs/GitHubDriver.php
index 548db6e26..ad05de78a 100644
--- a/src/Composer/Repository/Vcs/GitHubDriver.php
+++ b/src/Composer/Repository/Vcs/GitHubDriver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/Vcs/GitLabDriver.php b/src/Composer/Repository/Vcs/GitLabDriver.php
index a21ca6083..d80157f37 100644
--- a/src/Composer/Repository/Vcs/GitLabDriver.php
+++ b/src/Composer/Repository/Vcs/GitLabDriver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/Vcs/HgDriver.php b/src/Composer/Repository/Vcs/HgDriver.php
index 1faa3c3e3..70f69cbb3 100644
--- a/src/Composer/Repository/Vcs/HgDriver.php
+++ b/src/Composer/Repository/Vcs/HgDriver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/Vcs/PerforceDriver.php b/src/Composer/Repository/Vcs/PerforceDriver.php
index 1caad14a7..92459fdab 100644
--- a/src/Composer/Repository/Vcs/PerforceDriver.php
+++ b/src/Composer/Repository/Vcs/PerforceDriver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/Vcs/SvnDriver.php b/src/Composer/Repository/Vcs/SvnDriver.php
index 0c028b369..b4c4064a5 100644
--- a/src/Composer/Repository/Vcs/SvnDriver.php
+++ b/src/Composer/Repository/Vcs/SvnDriver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/Vcs/VcsDriver.php b/src/Composer/Repository/Vcs/VcsDriver.php
index 8656aa69d..f0c3af1ca 100644
--- a/src/Composer/Repository/Vcs/VcsDriver.php
+++ b/src/Composer/Repository/Vcs/VcsDriver.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/Vcs/VcsDriverInterface.php b/src/Composer/Repository/Vcs/VcsDriverInterface.php
index 9acf2e702..4a05e8d4b 100644
--- a/src/Composer/Repository/Vcs/VcsDriverInterface.php
+++ b/src/Composer/Repository/Vcs/VcsDriverInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/VcsRepository.php b/src/Composer/Repository/VcsRepository.php
index 9978413c7..41587f5b5 100644
--- a/src/Composer/Repository/VcsRepository.php
+++ b/src/Composer/Repository/VcsRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/VersionCacheInterface.php b/src/Composer/Repository/VersionCacheInterface.php
index 93572c10a..520007a98 100644
--- a/src/Composer/Repository/VersionCacheInterface.php
+++ b/src/Composer/Repository/VersionCacheInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/WritableArrayRepository.php b/src/Composer/Repository/WritableArrayRepository.php
index 6f98ad18d..acf317e00 100644
--- a/src/Composer/Repository/WritableArrayRepository.php
+++ b/src/Composer/Repository/WritableArrayRepository.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Repository/WritableRepositoryInterface.php b/src/Composer/Repository/WritableRepositoryInterface.php
index 8e7eac21e..46a3c9ea1 100644
--- a/src/Composer/Repository/WritableRepositoryInterface.php
+++ b/src/Composer/Repository/WritableRepositoryInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Script/Event.php b/src/Composer/Script/Event.php
index 0f05a7291..4b8ba2468 100644
--- a/src/Composer/Script/Event.php
+++ b/src/Composer/Script/Event.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Script/ScriptEvents.php b/src/Composer/Script/ScriptEvents.php
index 33cc4f57d..1c4024885 100644
--- a/src/Composer/Script/ScriptEvents.php
+++ b/src/Composer/Script/ScriptEvents.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/SelfUpdate/Keys.php b/src/Composer/SelfUpdate/Keys.php
index e8ce93045..72df28fd7 100644
--- a/src/Composer/SelfUpdate/Keys.php
+++ b/src/Composer/SelfUpdate/Keys.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/SelfUpdate/Versions.php b/src/Composer/SelfUpdate/Versions.php
index ea51319f7..40301eb20 100644
--- a/src/Composer/SelfUpdate/Versions.php
+++ b/src/Composer/SelfUpdate/Versions.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/AuthHelper.php b/src/Composer/Util/AuthHelper.php
index 54cb83f58..39c3691f4 100644
--- a/src/Composer/Util/AuthHelper.php
+++ b/src/Composer/Util/AuthHelper.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Bitbucket.php b/src/Composer/Util/Bitbucket.php
index b80eb37be..970225560 100644
--- a/src/Composer/Util/Bitbucket.php
+++ b/src/Composer/Util/Bitbucket.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/ComposerMirror.php b/src/Composer/Util/ComposerMirror.php
index 26afb80e5..9fb9f158c 100644
--- a/src/Composer/Util/ComposerMirror.php
+++ b/src/Composer/Util/ComposerMirror.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/ConfigValidator.php b/src/Composer/Util/ConfigValidator.php
index ea84c10b2..3e00b85c7 100644
--- a/src/Composer/Util/ConfigValidator.php
+++ b/src/Composer/Util/ConfigValidator.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/ErrorHandler.php b/src/Composer/Util/ErrorHandler.php
index fa2459e2c..80a0f9eed 100644
--- a/src/Composer/Util/ErrorHandler.php
+++ b/src/Composer/Util/ErrorHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Filesystem.php b/src/Composer/Util/Filesystem.php
index c60dd80ec..6d089017e 100644
--- a/src/Composer/Util/Filesystem.php
+++ b/src/Composer/Util/Filesystem.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Git.php b/src/Composer/Util/Git.php
index f28271c74..2c9167f56 100644
--- a/src/Composer/Util/Git.php
+++ b/src/Composer/Util/Git.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/GitHub.php b/src/Composer/Util/GitHub.php
index 4390bb8ac..5d22400e8 100644
--- a/src/Composer/Util/GitHub.php
+++ b/src/Composer/Util/GitHub.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/GitLab.php b/src/Composer/Util/GitLab.php
index 97c920dde..8f453efaa 100644
--- a/src/Composer/Util/GitLab.php
+++ b/src/Composer/Util/GitLab.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Hg.php b/src/Composer/Util/Hg.php
index 7797fe1a4..8c2412239 100644
--- a/src/Composer/Util/Hg.php
+++ b/src/Composer/Util/Hg.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Http/CurlDownloader.php b/src/Composer/Util/Http/CurlDownloader.php
index 327c09976..df64f0742 100644
--- a/src/Composer/Util/Http/CurlDownloader.php
+++ b/src/Composer/Util/Http/CurlDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Http/CurlResponse.php b/src/Composer/Util/Http/CurlResponse.php
index c51ff5069..41c703727 100644
--- a/src/Composer/Util/Http/CurlResponse.php
+++ b/src/Composer/Util/Http/CurlResponse.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Http/ProxyHelper.php b/src/Composer/Util/Http/ProxyHelper.php
index 49c89c215..a83fd454a 100644
--- a/src/Composer/Util/Http/ProxyHelper.php
+++ b/src/Composer/Util/Http/ProxyHelper.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Http/ProxyManager.php b/src/Composer/Util/Http/ProxyManager.php
index df7db9f5f..fa91bf7e0 100644
--- a/src/Composer/Util/Http/ProxyManager.php
+++ b/src/Composer/Util/Http/ProxyManager.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Http/RequestProxy.php b/src/Composer/Util/Http/RequestProxy.php
index eaf3f9452..36a5fdbab 100644
--- a/src/Composer/Util/Http/RequestProxy.php
+++ b/src/Composer/Util/Http/RequestProxy.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Http/Response.php b/src/Composer/Util/Http/Response.php
index 5556b6754..1c685265c 100644
--- a/src/Composer/Util/Http/Response.php
+++ b/src/Composer/Util/Http/Response.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/HttpDownloader.php b/src/Composer/Util/HttpDownloader.php
index b39108724..b70e0682f 100644
--- a/src/Composer/Util/HttpDownloader.php
+++ b/src/Composer/Util/HttpDownloader.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/IniHelper.php b/src/Composer/Util/IniHelper.php
index 699f22513..111ad66d5 100644
--- a/src/Composer/Util/IniHelper.php
+++ b/src/Composer/Util/IniHelper.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Loop.php b/src/Composer/Util/Loop.php
index 48edc1e16..cc4d08c9f 100644
--- a/src/Composer/Util/Loop.php
+++ b/src/Composer/Util/Loop.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/MetadataMinifier.php b/src/Composer/Util/MetadataMinifier.php
index 6fae871c3..ff93821dd 100644
--- a/src/Composer/Util/MetadataMinifier.php
+++ b/src/Composer/Util/MetadataMinifier.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/NoProxyPattern.php b/src/Composer/Util/NoProxyPattern.php
index 2ae475561..857095b66 100644
--- a/src/Composer/Util/NoProxyPattern.php
+++ b/src/Composer/Util/NoProxyPattern.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/PackageInfo.php b/src/Composer/Util/PackageInfo.php
index 84277c731..0b2607ac9 100644
--- a/src/Composer/Util/PackageInfo.php
+++ b/src/Composer/Util/PackageInfo.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/PackageSorter.php b/src/Composer/Util/PackageSorter.php
index 62889961a..83ae4da37 100644
--- a/src/Composer/Util/PackageSorter.php
+++ b/src/Composer/Util/PackageSorter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Perforce.php b/src/Composer/Util/Perforce.php
index ee21169e1..65d2a0318 100644
--- a/src/Composer/Util/Perforce.php
+++ b/src/Composer/Util/Perforce.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Platform.php b/src/Composer/Util/Platform.php
index 4e58cecbb..eb71673a2 100644
--- a/src/Composer/Util/Platform.php
+++ b/src/Composer/Util/Platform.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/ProcessExecutor.php b/src/Composer/Util/ProcessExecutor.php
index aa9bb5eaf..d2572a02e 100644
--- a/src/Composer/Util/ProcessExecutor.php
+++ b/src/Composer/Util/ProcessExecutor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/RemoteFilesystem.php b/src/Composer/Util/RemoteFilesystem.php
index 4d666fc30..5aa7d6685 100644
--- a/src/Composer/Util/RemoteFilesystem.php
+++ b/src/Composer/Util/RemoteFilesystem.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Silencer.php b/src/Composer/Util/Silencer.php
index 484b5a5c7..c01404be6 100644
--- a/src/Composer/Util/Silencer.php
+++ b/src/Composer/Util/Silencer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/StreamContextFactory.php b/src/Composer/Util/StreamContextFactory.php
index a4b1dbd4a..99a5d96c2 100644
--- a/src/Composer/Util/StreamContextFactory.php
+++ b/src/Composer/Util/StreamContextFactory.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Svn.php b/src/Composer/Util/Svn.php
index 00a090d5c..db5950696 100644
--- a/src/Composer/Util/Svn.php
+++ b/src/Composer/Util/Svn.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/SyncHelper.php b/src/Composer/Util/SyncHelper.php
index c245d2132..819115d83 100644
--- a/src/Composer/Util/SyncHelper.php
+++ b/src/Composer/Util/SyncHelper.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Tar.php b/src/Composer/Util/Tar.php
index 05f2229f0..489565b1b 100644
--- a/src/Composer/Util/Tar.php
+++ b/src/Composer/Util/Tar.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/TlsHelper.php b/src/Composer/Util/TlsHelper.php
index 78829e60e..95f94887f 100644
--- a/src/Composer/Util/TlsHelper.php
+++ b/src/Composer/Util/TlsHelper.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Url.php b/src/Composer/Util/Url.php
index 6089da925..c30e4199d 100644
--- a/src/Composer/Util/Url.php
+++ b/src/Composer/Util/Url.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/Composer/Util/Zip.php b/src/Composer/Util/Zip.php
index 342c1d3b7..20c33771b 100644
--- a/src/Composer/Util/Zip.php
+++ b/src/Composer/Util/Zip.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/src/bootstrap.php b/src/bootstrap.php
index 3b2cb4d85..886b4ff0c 100644
--- a/src/bootstrap.php
+++ b/src/bootstrap.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/AllFunctionalTest.php b/tests/Composer/Test/AllFunctionalTest.php
index a46b49859..81ee7b382 100644
--- a/tests/Composer/Test/AllFunctionalTest.php
+++ b/tests/Composer/Test/AllFunctionalTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/ApplicationTest.php b/tests/Composer/Test/ApplicationTest.php
index 151eca5b4..8effc0684 100644
--- a/tests/Composer/Test/ApplicationTest.php
+++ b/tests/Composer/Test/ApplicationTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
index 6a3fbec83..27c444bec 100644
--- a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Autoload/ClassLoaderTest.php b/tests/Composer/Test/Autoload/ClassLoaderTest.php
index 27f96d6b7..81d6f5fd0 100644
--- a/tests/Composer/Test/Autoload/ClassLoaderTest.php
+++ b/tests/Composer/Test/Autoload/ClassLoaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php b/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
index 302ab6094..f38402620 100644
--- a/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/CacheTest.php b/tests/Composer/Test/CacheTest.php
index 703650db3..62b0d877d 100644
--- a/tests/Composer/Test/CacheTest.php
+++ b/tests/Composer/Test/CacheTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Command/ArchiveCommandTest.php b/tests/Composer/Test/Command/ArchiveCommandTest.php
index 9ad7bf73f..0d7b07401 100644
--- a/tests/Composer/Test/Command/ArchiveCommandTest.php
+++ b/tests/Composer/Test/Command/ArchiveCommandTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Command/InitCommandTest.php b/tests/Composer/Test/Command/InitCommandTest.php
index f33f730b9..ae1a6184c 100644
--- a/tests/Composer/Test/Command/InitCommandTest.php
+++ b/tests/Composer/Test/Command/InitCommandTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Command/RunScriptCommandTest.php b/tests/Composer/Test/Command/RunScriptCommandTest.php
index 200ae7c9a..c52fdb889 100644
--- a/tests/Composer/Test/Command/RunScriptCommandTest.php
+++ b/tests/Composer/Test/Command/RunScriptCommandTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/ComposerTest.php b/tests/Composer/Test/ComposerTest.php
index 216245a49..2cbd54544 100644
--- a/tests/Composer/Test/ComposerTest.php
+++ b/tests/Composer/Test/ComposerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Config/JsonConfigSourceTest.php b/tests/Composer/Test/Config/JsonConfigSourceTest.php
index 818e22db3..6192fd5a3 100644
--- a/tests/Composer/Test/Config/JsonConfigSourceTest.php
+++ b/tests/Composer/Test/Config/JsonConfigSourceTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/ConfigTest.php b/tests/Composer/Test/ConfigTest.php
index 924806e60..73d20f58a 100644
--- a/tests/Composer/Test/ConfigTest.php
+++ b/tests/Composer/Test/ConfigTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Console/HtmlOutputFormatterTest.php b/tests/Composer/Test/Console/HtmlOutputFormatterTest.php
index 60865f726..46ab0caab 100644
--- a/tests/Composer/Test/Console/HtmlOutputFormatterTest.php
+++ b/tests/Composer/Test/Console/HtmlOutputFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DefaultConfigTest.php b/tests/Composer/Test/DefaultConfigTest.php
index 0b5f694ea..a49a98ef8 100644
--- a/tests/Composer/Test/DefaultConfigTest.php
+++ b/tests/Composer/Test/DefaultConfigTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DependencyResolver/DefaultPolicyTest.php b/tests/Composer/Test/DependencyResolver/DefaultPolicyTest.php
index 27569baee..4d0c3c136 100644
--- a/tests/Composer/Test/DependencyResolver/DefaultPolicyTest.php
+++ b/tests/Composer/Test/DependencyResolver/DefaultPolicyTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php b/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php
index 847b374d4..7e6249113 100644
--- a/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php
+++ b/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DependencyResolver/PoolOptimizerTest.php b/tests/Composer/Test/DependencyResolver/PoolOptimizerTest.php
index 37e7346fc..18ef95dc3 100644
--- a/tests/Composer/Test/DependencyResolver/PoolOptimizerTest.php
+++ b/tests/Composer/Test/DependencyResolver/PoolOptimizerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DependencyResolver/PoolTest.php b/tests/Composer/Test/DependencyResolver/PoolTest.php
index 3d24f9fdf..6952955d8 100644
--- a/tests/Composer/Test/DependencyResolver/PoolTest.php
+++ b/tests/Composer/Test/DependencyResolver/PoolTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DependencyResolver/RequestTest.php b/tests/Composer/Test/DependencyResolver/RequestTest.php
index c3fff4a0e..a749be8bf 100644
--- a/tests/Composer/Test/DependencyResolver/RequestTest.php
+++ b/tests/Composer/Test/DependencyResolver/RequestTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DependencyResolver/RuleSetIteratorTest.php b/tests/Composer/Test/DependencyResolver/RuleSetIteratorTest.php
index 807311882..7e55c7013 100644
--- a/tests/Composer/Test/DependencyResolver/RuleSetIteratorTest.php
+++ b/tests/Composer/Test/DependencyResolver/RuleSetIteratorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DependencyResolver/RuleSetTest.php b/tests/Composer/Test/DependencyResolver/RuleSetTest.php
index c891cb936..2912ebc3f 100644
--- a/tests/Composer/Test/DependencyResolver/RuleSetTest.php
+++ b/tests/Composer/Test/DependencyResolver/RuleSetTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DependencyResolver/RuleTest.php b/tests/Composer/Test/DependencyResolver/RuleTest.php
index ed1401936..9bd9e5377 100644
--- a/tests/Composer/Test/DependencyResolver/RuleTest.php
+++ b/tests/Composer/Test/DependencyResolver/RuleTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DependencyResolver/SolverTest.php b/tests/Composer/Test/DependencyResolver/SolverTest.php
index f3782f2fb..a3c2e3d3a 100644
--- a/tests/Composer/Test/DependencyResolver/SolverTest.php
+++ b/tests/Composer/Test/DependencyResolver/SolverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/DependencyResolver/TransactionTest.php b/tests/Composer/Test/DependencyResolver/TransactionTest.php
index 0f1182d84..0cb73d3fc 100644
--- a/tests/Composer/Test/DependencyResolver/TransactionTest.php
+++ b/tests/Composer/Test/DependencyResolver/TransactionTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Downloader/ArchiveDownloaderTest.php b/tests/Composer/Test/Downloader/ArchiveDownloaderTest.php
index 4b95b2bd9..c0d4d7ee7 100644
--- a/tests/Composer/Test/Downloader/ArchiveDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/ArchiveDownloaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Downloader/DownloadManagerTest.php b/tests/Composer/Test/Downloader/DownloadManagerTest.php
index 8ff051927..f587f703b 100644
--- a/tests/Composer/Test/Downloader/DownloadManagerTest.php
+++ b/tests/Composer/Test/Downloader/DownloadManagerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Downloader/FileDownloaderTest.php b/tests/Composer/Test/Downloader/FileDownloaderTest.php
index c14735162..8ed93f9ac 100644
--- a/tests/Composer/Test/Downloader/FileDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/FileDownloaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Downloader/FossilDownloaderTest.php b/tests/Composer/Test/Downloader/FossilDownloaderTest.php
index ebe9cf75e..7a080c8b8 100644
--- a/tests/Composer/Test/Downloader/FossilDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/FossilDownloaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Downloader/GitDownloaderTest.php b/tests/Composer/Test/Downloader/GitDownloaderTest.php
index 91b90b369..8a65686d6 100644
--- a/tests/Composer/Test/Downloader/GitDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/GitDownloaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Downloader/HgDownloaderTest.php b/tests/Composer/Test/Downloader/HgDownloaderTest.php
index 3c5712b4c..45b84a1ff 100644
--- a/tests/Composer/Test/Downloader/HgDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/HgDownloaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Downloader/PerforceDownloaderTest.php b/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
index f8a8e16c6..f81486106 100644
--- a/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Downloader/XzDownloaderTest.php b/tests/Composer/Test/Downloader/XzDownloaderTest.php
index f20129bfb..1f060c16a 100644
--- a/tests/Composer/Test/Downloader/XzDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/XzDownloaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Downloader/ZipDownloaderTest.php b/tests/Composer/Test/Downloader/ZipDownloaderTest.php
index f7a444412..9ba06d180 100644
--- a/tests/Composer/Test/Downloader/ZipDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/ZipDownloaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php b/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php
index fc57a1241..05ca1a272 100644
--- a/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php
+++ b/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/FactoryTest.php b/tests/Composer/Test/FactoryTest.php
index ec41827fb..636e58c31 100644
--- a/tests/Composer/Test/FactoryTest.php
+++ b/tests/Composer/Test/FactoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilterTest.php b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilterTest.php
index 1c3b79a6e..97a43bf80 100644
--- a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilterTest.php
+++ b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilterTest.php b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilterTest.php
index dd1f71d85..6de438ff1 100644
--- a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilterTest.php
+++ b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilterTest.php b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilterTest.php
index 02b6ad50c..239c954c1 100644
--- a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilterTest.php
+++ b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactoryTest.php b/tests/Composer/Test/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactoryTest.php
index d443532e3..ce2055e39 100644
--- a/tests/Composer/Test/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactoryTest.php
+++ b/tests/Composer/Test/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/IO/BufferIOTest.php b/tests/Composer/Test/IO/BufferIOTest.php
index 8e86f1903..0e2d11101 100644
--- a/tests/Composer/Test/IO/BufferIOTest.php
+++ b/tests/Composer/Test/IO/BufferIOTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/IO/ConsoleIOTest.php b/tests/Composer/Test/IO/ConsoleIOTest.php
index 65995c884..8a0799acf 100644
--- a/tests/Composer/Test/IO/ConsoleIOTest.php
+++ b/tests/Composer/Test/IO/ConsoleIOTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/IO/NullIOTest.php b/tests/Composer/Test/IO/NullIOTest.php
index b2ecc84d8..d43c891fe 100644
--- a/tests/Composer/Test/IO/NullIOTest.php
+++ b/tests/Composer/Test/IO/NullIOTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/InstalledVersionsTest.php b/tests/Composer/Test/InstalledVersionsTest.php
index e23e90ece..9e06f4c2c 100644
--- a/tests/Composer/Test/InstalledVersionsTest.php
+++ b/tests/Composer/Test/InstalledVersionsTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Installer/BinaryInstallerTest.php b/tests/Composer/Test/Installer/BinaryInstallerTest.php
index 28b1f0fc0..a7e49fe68 100644
--- a/tests/Composer/Test/Installer/BinaryInstallerTest.php
+++ b/tests/Composer/Test/Installer/BinaryInstallerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Installer/InstallationManagerTest.php b/tests/Composer/Test/Installer/InstallationManagerTest.php
index 91057a72a..5b3d4b428 100644
--- a/tests/Composer/Test/Installer/InstallationManagerTest.php
+++ b/tests/Composer/Test/Installer/InstallationManagerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Installer/InstallerEventTest.php b/tests/Composer/Test/Installer/InstallerEventTest.php
index d2146f3a7..834f7ac7b 100644
--- a/tests/Composer/Test/Installer/InstallerEventTest.php
+++ b/tests/Composer/Test/Installer/InstallerEventTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Installer/LibraryInstallerTest.php b/tests/Composer/Test/Installer/LibraryInstallerTest.php
index e14a830df..013966175 100644
--- a/tests/Composer/Test/Installer/LibraryInstallerTest.php
+++ b/tests/Composer/Test/Installer/LibraryInstallerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Installer/MetapackageInstallerTest.php b/tests/Composer/Test/Installer/MetapackageInstallerTest.php
index 0b0b2035a..114c3f95b 100644
--- a/tests/Composer/Test/Installer/MetapackageInstallerTest.php
+++ b/tests/Composer/Test/Installer/MetapackageInstallerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php b/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php
index 5cd693d4f..e7fada87b 100644
--- a/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php
+++ b/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/InstallerTest.php b/tests/Composer/Test/InstallerTest.php
index e22264338..1fc54dc4d 100644
--- a/tests/Composer/Test/InstallerTest.php
+++ b/tests/Composer/Test/InstallerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Json/ComposerSchemaTest.php b/tests/Composer/Test/Json/ComposerSchemaTest.php
index e6aea2271..a458ef1a0 100644
--- a/tests/Composer/Test/Json/ComposerSchemaTest.php
+++ b/tests/Composer/Test/Json/ComposerSchemaTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Json/JsonFileTest.php b/tests/Composer/Test/Json/JsonFileTest.php
index 02ede63dc..fa393fc41 100644
--- a/tests/Composer/Test/Json/JsonFileTest.php
+++ b/tests/Composer/Test/Json/JsonFileTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Json/JsonFormatterTest.php b/tests/Composer/Test/Json/JsonFormatterTest.php
index cd95c6fc9..88f76dfec 100644
--- a/tests/Composer/Test/Json/JsonFormatterTest.php
+++ b/tests/Composer/Test/Json/JsonFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Json/JsonManipulatorTest.php b/tests/Composer/Test/Json/JsonManipulatorTest.php
index 533751132..0e32be3bc 100644
--- a/tests/Composer/Test/Json/JsonManipulatorTest.php
+++ b/tests/Composer/Test/Json/JsonManipulatorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Json/JsonValidationExceptionTest.php b/tests/Composer/Test/Json/JsonValidationExceptionTest.php
index 863368303..f11dfca88 100644
--- a/tests/Composer/Test/Json/JsonValidationExceptionTest.php
+++ b/tests/Composer/Test/Json/JsonValidationExceptionTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Mock/FactoryMock.php b/tests/Composer/Test/Mock/FactoryMock.php
index 17e21c83b..6c75c3e6b 100644
--- a/tests/Composer/Test/Mock/FactoryMock.php
+++ b/tests/Composer/Test/Mock/FactoryMock.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Mock/HttpDownloaderMock.php b/tests/Composer/Test/Mock/HttpDownloaderMock.php
index b919b294b..beb12ecc8 100644
--- a/tests/Composer/Test/Mock/HttpDownloaderMock.php
+++ b/tests/Composer/Test/Mock/HttpDownloaderMock.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Mock/InstallationManagerMock.php b/tests/Composer/Test/Mock/InstallationManagerMock.php
index ed4eaa873..593093ded 100644
--- a/tests/Composer/Test/Mock/InstallationManagerMock.php
+++ b/tests/Composer/Test/Mock/InstallationManagerMock.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Mock/InstalledFilesystemRepositoryMock.php b/tests/Composer/Test/Mock/InstalledFilesystemRepositoryMock.php
index 101005cda..b75b5df8c 100644
--- a/tests/Composer/Test/Mock/InstalledFilesystemRepositoryMock.php
+++ b/tests/Composer/Test/Mock/InstalledFilesystemRepositoryMock.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Mock/ProcessExecutorMock.php b/tests/Composer/Test/Mock/ProcessExecutorMock.php
index b3e7d176e..b8948e6ae 100644
--- a/tests/Composer/Test/Mock/ProcessExecutorMock.php
+++ b/tests/Composer/Test/Mock/ProcessExecutorMock.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Mock/VersionGuesserMock.php b/tests/Composer/Test/Mock/VersionGuesserMock.php
index b634b0297..c8a0c95d0 100644
--- a/tests/Composer/Test/Mock/VersionGuesserMock.php
+++ b/tests/Composer/Test/Mock/VersionGuesserMock.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php b/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php
index 2fb91a2b2..7fe88cb41 100644
--- a/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php
+++ b/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php b/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
index 04f098355..5a898694b 100644
--- a/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
+++ b/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Archiver/ArchiverTest.php b/tests/Composer/Test/Package/Archiver/ArchiverTest.php
index eecd8dff2..13c4ed0f7 100644
--- a/tests/Composer/Test/Package/Archiver/ArchiverTest.php
+++ b/tests/Composer/Test/Package/Archiver/ArchiverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Archiver/GitExcludeFilterTest.php b/tests/Composer/Test/Package/Archiver/GitExcludeFilterTest.php
index 32c255cfc..79c57f0d0 100644
--- a/tests/Composer/Test/Package/Archiver/GitExcludeFilterTest.php
+++ b/tests/Composer/Test/Package/Archiver/GitExcludeFilterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Archiver/PharArchiverTest.php b/tests/Composer/Test/Package/Archiver/PharArchiverTest.php
index 22ebb83d5..0ad1d4eb5 100644
--- a/tests/Composer/Test/Package/Archiver/PharArchiverTest.php
+++ b/tests/Composer/Test/Package/Archiver/PharArchiverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Archiver/ZipArchiverTest.php b/tests/Composer/Test/Package/Archiver/ZipArchiverTest.php
index 7e4fb7f89..e216fe0a6 100644
--- a/tests/Composer/Test/Package/Archiver/ZipArchiverTest.php
+++ b/tests/Composer/Test/Package/Archiver/ZipArchiverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/BasePackageTest.php b/tests/Composer/Test/Package/BasePackageTest.php
index 90921bc7c..acc8f4de3 100644
--- a/tests/Composer/Test/Package/BasePackageTest.php
+++ b/tests/Composer/Test/Package/BasePackageTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/CompletePackageTest.php b/tests/Composer/Test/Package/CompletePackageTest.php
index 4f57dff14..a1edd1560 100644
--- a/tests/Composer/Test/Package/CompletePackageTest.php
+++ b/tests/Composer/Test/Package/CompletePackageTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php b/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php
index 8b1d5af0c..a4b3fc0d2 100644
--- a/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php
+++ b/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php b/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php
index 2324ad0c2..fa2a180a9 100644
--- a/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php
+++ b/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php b/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php
index a669f669f..7f8872fc1 100644
--- a/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php
+++ b/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Loader/ValidatingArrayLoaderTest.php b/tests/Composer/Test/Package/Loader/ValidatingArrayLoaderTest.php
index a8204a76f..fd105f7e1 100644
--- a/tests/Composer/Test/Package/Loader/ValidatingArrayLoaderTest.php
+++ b/tests/Composer/Test/Package/Loader/ValidatingArrayLoaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/LockerTest.php b/tests/Composer/Test/Package/LockerTest.php
index d2913e36d..34e8be360 100644
--- a/tests/Composer/Test/Package/LockerTest.php
+++ b/tests/Composer/Test/Package/LockerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/RootAliasPackageTest.php b/tests/Composer/Test/Package/RootAliasPackageTest.php
index 0a42fd31d..c871cd1f5 100644
--- a/tests/Composer/Test/Package/RootAliasPackageTest.php
+++ b/tests/Composer/Test/Package/RootAliasPackageTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Version/VersionGuesserTest.php b/tests/Composer/Test/Package/Version/VersionGuesserTest.php
index 4ec717681..e5076862a 100644
--- a/tests/Composer/Test/Package/Version/VersionGuesserTest.php
+++ b/tests/Composer/Test/Package/Version/VersionGuesserTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Version/VersionParserTest.php b/tests/Composer/Test/Package/Version/VersionParserTest.php
index 2f120a7f8..5f2109e8e 100644
--- a/tests/Composer/Test/Package/Version/VersionParserTest.php
+++ b/tests/Composer/Test/Package/Version/VersionParserTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Package/Version/VersionSelectorTest.php b/tests/Composer/Test/Package/Version/VersionSelectorTest.php
index 4ff61029c..1cf08155e 100644
--- a/tests/Composer/Test/Package/Version/VersionSelectorTest.php
+++ b/tests/Composer/Test/Package/Version/VersionSelectorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Platform/HhvmDetectorTest.php b/tests/Composer/Test/Platform/HhvmDetectorTest.php
index eaf93c982..c39395ff1 100644
--- a/tests/Composer/Test/Platform/HhvmDetectorTest.php
+++ b/tests/Composer/Test/Platform/HhvmDetectorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Platform/VersionTest.php b/tests/Composer/Test/Platform/VersionTest.php
index 4ae361bb5..00497ef94 100644
--- a/tests/Composer/Test/Platform/VersionTest.php
+++ b/tests/Composer/Test/Platform/VersionTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Plugin/Mock/Capability.php b/tests/Composer/Test/Plugin/Mock/Capability.php
index a9dd4accb..f7cb608b4 100644
--- a/tests/Composer/Test/Plugin/Mock/Capability.php
+++ b/tests/Composer/Test/Plugin/Mock/Capability.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Plugin/Mock/CapablePluginInterface.php b/tests/Composer/Test/Plugin/Mock/CapablePluginInterface.php
index 5e8d88c31..9f84554aa 100644
--- a/tests/Composer/Test/Plugin/Mock/CapablePluginInterface.php
+++ b/tests/Composer/Test/Plugin/Mock/CapablePluginInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Plugin/PluginInstallerTest.php b/tests/Composer/Test/Plugin/PluginInstallerTest.php
index 32b2afc36..99392e084 100644
--- a/tests/Composer/Test/Plugin/PluginInstallerTest.php
+++ b/tests/Composer/Test/Plugin/PluginInstallerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Question/StrictConfirmationQuestionTest.php b/tests/Composer/Test/Question/StrictConfirmationQuestionTest.php
index 2c21d869d..c85f38cef 100644
--- a/tests/Composer/Test/Question/StrictConfirmationQuestionTest.php
+++ b/tests/Composer/Test/Question/StrictConfirmationQuestionTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/ArrayRepositoryTest.php b/tests/Composer/Test/Repository/ArrayRepositoryTest.php
index f2261eac2..04c45959f 100644
--- a/tests/Composer/Test/Repository/ArrayRepositoryTest.php
+++ b/tests/Composer/Test/Repository/ArrayRepositoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/ArtifactRepositoryTest.php b/tests/Composer/Test/Repository/ArtifactRepositoryTest.php
index ee44153a3..c038dfc2f 100644
--- a/tests/Composer/Test/Repository/ArtifactRepositoryTest.php
+++ b/tests/Composer/Test/Repository/ArtifactRepositoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/ComposerRepositoryTest.php b/tests/Composer/Test/Repository/ComposerRepositoryTest.php
index fcfc2fa4c..854a388ec 100644
--- a/tests/Composer/Test/Repository/ComposerRepositoryTest.php
+++ b/tests/Composer/Test/Repository/ComposerRepositoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/CompositeRepositoryTest.php b/tests/Composer/Test/Repository/CompositeRepositoryTest.php
index edf914e73..ca123a3b3 100644
--- a/tests/Composer/Test/Repository/CompositeRepositoryTest.php
+++ b/tests/Composer/Test/Repository/CompositeRepositoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/FilesystemRepositoryTest.php b/tests/Composer/Test/Repository/FilesystemRepositoryTest.php
index ad0466191..e16938334 100644
--- a/tests/Composer/Test/Repository/FilesystemRepositoryTest.php
+++ b/tests/Composer/Test/Repository/FilesystemRepositoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/FilterRepositoryTest.php b/tests/Composer/Test/Repository/FilterRepositoryTest.php
index eb96d876f..7fa24236a 100644
--- a/tests/Composer/Test/Repository/FilterRepositoryTest.php
+++ b/tests/Composer/Test/Repository/FilterRepositoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/InstalledRepositoryTest.php b/tests/Composer/Test/Repository/InstalledRepositoryTest.php
index c4f32a1a5..e9efc04ff 100644
--- a/tests/Composer/Test/Repository/InstalledRepositoryTest.php
+++ b/tests/Composer/Test/Repository/InstalledRepositoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/PathRepositoryTest.php b/tests/Composer/Test/Repository/PathRepositoryTest.php
index 5d6888787..b82837d93 100644
--- a/tests/Composer/Test/Repository/PathRepositoryTest.php
+++ b/tests/Composer/Test/Repository/PathRepositoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/PlatformRepositoryTest.php b/tests/Composer/Test/Repository/PlatformRepositoryTest.php
index 18c2a68d8..0b672729b 100644
--- a/tests/Composer/Test/Repository/PlatformRepositoryTest.php
+++ b/tests/Composer/Test/Repository/PlatformRepositoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/RepositoryFactoryTest.php b/tests/Composer/Test/Repository/RepositoryFactoryTest.php
index 3928d0288..beb8be483 100644
--- a/tests/Composer/Test/Repository/RepositoryFactoryTest.php
+++ b/tests/Composer/Test/Repository/RepositoryFactoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/RepositoryManagerTest.php b/tests/Composer/Test/Repository/RepositoryManagerTest.php
index fcf826e14..e5b4c84da 100644
--- a/tests/Composer/Test/Repository/RepositoryManagerTest.php
+++ b/tests/Composer/Test/Repository/RepositoryManagerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/Vcs/FossilDriverTest.php b/tests/Composer/Test/Repository/Vcs/FossilDriverTest.php
index 1857cf262..f43e8c02e 100644
--- a/tests/Composer/Test/Repository/Vcs/FossilDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/FossilDriverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php b/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php
index d616e3798..7a5d30654 100644
--- a/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php b/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
index 005f0c817..bcacb53a6 100644
--- a/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/Vcs/GitLabDriverTest.php b/tests/Composer/Test/Repository/Vcs/GitLabDriverTest.php
index 368655ec2..1aeeb23d4 100644
--- a/tests/Composer/Test/Repository/Vcs/GitLabDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/GitLabDriverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/Vcs/HgDriverTest.php b/tests/Composer/Test/Repository/Vcs/HgDriverTest.php
index 0d6948415..58cac0c16 100644
--- a/tests/Composer/Test/Repository/Vcs/HgDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/HgDriverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php b/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
index fda883a43..98ee5f3ea 100644
--- a/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php b/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php
index e18f64af3..d6310ebf5 100644
--- a/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Repository/VcsRepositoryTest.php b/tests/Composer/Test/Repository/VcsRepositoryTest.php
index a4e175397..ac5884584 100644
--- a/tests/Composer/Test/Repository/VcsRepositoryTest.php
+++ b/tests/Composer/Test/Repository/VcsRepositoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Script/EventTest.php b/tests/Composer/Test/Script/EventTest.php
index 724d0e886..102d6e5f5 100644
--- a/tests/Composer/Test/Script/EventTest.php
+++ b/tests/Composer/Test/Script/EventTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/TestCase.php b/tests/Composer/Test/TestCase.php
index 0e61bb87a..a26dbfb6e 100644
--- a/tests/Composer/Test/TestCase.php
+++ b/tests/Composer/Test/TestCase.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/AuthHelperTest.php b/tests/Composer/Test/Util/AuthHelperTest.php
index b179688e2..f38b375aa 100644
--- a/tests/Composer/Test/Util/AuthHelperTest.php
+++ b/tests/Composer/Test/Util/AuthHelperTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/BitbucketTest.php b/tests/Composer/Test/Util/BitbucketTest.php
index 525e90456..5d1b83c25 100644
--- a/tests/Composer/Test/Util/BitbucketTest.php
+++ b/tests/Composer/Test/Util/BitbucketTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/ConfigValidatorTest.php b/tests/Composer/Test/Util/ConfigValidatorTest.php
index c755ea6e5..cdbb87851 100644
--- a/tests/Composer/Test/Util/ConfigValidatorTest.php
+++ b/tests/Composer/Test/Util/ConfigValidatorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/ErrorHandlerTest.php b/tests/Composer/Test/Util/ErrorHandlerTest.php
index 4def526a4..7d48d8963 100644
--- a/tests/Composer/Test/Util/ErrorHandlerTest.php
+++ b/tests/Composer/Test/Util/ErrorHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/FilesystemTest.php b/tests/Composer/Test/Util/FilesystemTest.php
index 20298d534..e40e53267 100644
--- a/tests/Composer/Test/Util/FilesystemTest.php
+++ b/tests/Composer/Test/Util/FilesystemTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/GitHubTest.php b/tests/Composer/Test/Util/GitHubTest.php
index a4151f489..72b2e1c2c 100644
--- a/tests/Composer/Test/Util/GitHubTest.php
+++ b/tests/Composer/Test/Util/GitHubTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/GitLabTest.php b/tests/Composer/Test/Util/GitLabTest.php
index 61bc35c72..d1f44d946 100644
--- a/tests/Composer/Test/Util/GitLabTest.php
+++ b/tests/Composer/Test/Util/GitLabTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/GitTest.php b/tests/Composer/Test/Util/GitTest.php
index c91a34248..41602aa0b 100644
--- a/tests/Composer/Test/Util/GitTest.php
+++ b/tests/Composer/Test/Util/GitTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/Http/ProxyHelperTest.php b/tests/Composer/Test/Util/Http/ProxyHelperTest.php
index 4de4c654a..c70dd746d 100644
--- a/tests/Composer/Test/Util/Http/ProxyHelperTest.php
+++ b/tests/Composer/Test/Util/Http/ProxyHelperTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/Http/ProxyManagerTest.php b/tests/Composer/Test/Util/Http/ProxyManagerTest.php
index ea5eb78f7..ebdc4d290 100644
--- a/tests/Composer/Test/Util/Http/ProxyManagerTest.php
+++ b/tests/Composer/Test/Util/Http/ProxyManagerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/Http/RequestProxyTest.php b/tests/Composer/Test/Util/Http/RequestProxyTest.php
index 474c6857e..2073d70bf 100644
--- a/tests/Composer/Test/Util/Http/RequestProxyTest.php
+++ b/tests/Composer/Test/Util/Http/RequestProxyTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/HttpDownloaderTest.php b/tests/Composer/Test/Util/HttpDownloaderTest.php
index fe49c1ca5..26e778764 100644
--- a/tests/Composer/Test/Util/HttpDownloaderTest.php
+++ b/tests/Composer/Test/Util/HttpDownloaderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/IniHelperTest.php b/tests/Composer/Test/Util/IniHelperTest.php
index a3e8bc8e6..753efcee0 100644
--- a/tests/Composer/Test/Util/IniHelperTest.php
+++ b/tests/Composer/Test/Util/IniHelperTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/MetadataMinifierTest.php b/tests/Composer/Test/Util/MetadataMinifierTest.php
index 44e28c9b2..99f61c0b6 100644
--- a/tests/Composer/Test/Util/MetadataMinifierTest.php
+++ b/tests/Composer/Test/Util/MetadataMinifierTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/NoProxyPatternTest.php b/tests/Composer/Test/Util/NoProxyPatternTest.php
index 7b00da615..559875375 100644
--- a/tests/Composer/Test/Util/NoProxyPatternTest.php
+++ b/tests/Composer/Test/Util/NoProxyPatternTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/PackageSorterTest.php b/tests/Composer/Test/Util/PackageSorterTest.php
index 63734925f..67cdd13bb 100644
--- a/tests/Composer/Test/Util/PackageSorterTest.php
+++ b/tests/Composer/Test/Util/PackageSorterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/PerforceTest.php b/tests/Composer/Test/Util/PerforceTest.php
index 7b524337f..44617633a 100644
--- a/tests/Composer/Test/Util/PerforceTest.php
+++ b/tests/Composer/Test/Util/PerforceTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/PlatformTest.php b/tests/Composer/Test/Util/PlatformTest.php
index f05d3a736..b6be7b897 100644
--- a/tests/Composer/Test/Util/PlatformTest.php
+++ b/tests/Composer/Test/Util/PlatformTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/ProcessExecutorTest.php b/tests/Composer/Test/Util/ProcessExecutorTest.php
index c1aac5ad7..4e57e206f 100644
--- a/tests/Composer/Test/Util/ProcessExecutorTest.php
+++ b/tests/Composer/Test/Util/ProcessExecutorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/RemoteFilesystemTest.php b/tests/Composer/Test/Util/RemoteFilesystemTest.php
index eebe8f900..4fc7c7454 100644
--- a/tests/Composer/Test/Util/RemoteFilesystemTest.php
+++ b/tests/Composer/Test/Util/RemoteFilesystemTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/SilencerTest.php b/tests/Composer/Test/Util/SilencerTest.php
index 58a81eb92..0c9ad5777 100644
--- a/tests/Composer/Test/Util/SilencerTest.php
+++ b/tests/Composer/Test/Util/SilencerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/StreamContextFactoryTest.php b/tests/Composer/Test/Util/StreamContextFactoryTest.php
index ca78f1c4c..e16d9ad79 100644
--- a/tests/Composer/Test/Util/StreamContextFactoryTest.php
+++ b/tests/Composer/Test/Util/StreamContextFactoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/SvnTest.php b/tests/Composer/Test/Util/SvnTest.php
index b6d6062f9..4f5d2eaec 100644
--- a/tests/Composer/Test/Util/SvnTest.php
+++ b/tests/Composer/Test/Util/SvnTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/TarTest.php b/tests/Composer/Test/Util/TarTest.php
index b0e697819..86c7564cd 100644
--- a/tests/Composer/Test/Util/TarTest.php
+++ b/tests/Composer/Test/Util/TarTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/TlsHelperTest.php b/tests/Composer/Test/Util/TlsHelperTest.php
index c6f1514f0..b2692d473 100644
--- a/tests/Composer/Test/Util/TlsHelperTest.php
+++ b/tests/Composer/Test/Util/TlsHelperTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/UrlTest.php b/tests/Composer/Test/Util/UrlTest.php
index 3a8b084d5..1d26967e2 100644
--- a/tests/Composer/Test/Util/UrlTest.php
+++ b/tests/Composer/Test/Util/UrlTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/Composer/Test/Util/ZipTest.php b/tests/Composer/Test/Util/ZipTest.php
index fa92fd897..0af7ea89a 100644
--- a/tests/Composer/Test/Util/ZipTest.php
+++ b/tests/Composer/Test/Util/ZipTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index a35126cff..19279f406 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.
diff --git a/tests/console-application.php b/tests/console-application.php
index 4ee45c8ee..9a8b9750a 100644
--- a/tests/console-application.php
+++ b/tests/console-application.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of Composer.