diff --git a/src/Composer/Repository/RepositoryInterface.php b/src/Composer/Repository/RepositoryInterface.php
index 4223d12fb..f5f1204d0 100644
--- a/src/Composer/Repository/RepositoryInterface.php
+++ b/src/Composer/Repository/RepositoryInterface.php
@@ -86,8 +86,8 @@ interface RepositoryInterface extends \Countable
      * @param int    $mode  a set of SEARCH_* constants to search on, implementations should do a best effort only
      * @param string $type  The type of package to search for. Defaults to all types of packages
      *
-     * @return array[] an array of array('name' => '...', 'description' => '...')
-     * @phpstan-return list<array{name: string, description: string}>
+     * @return array[] an array of array('name' => '...', 'description' => '...'|null)
+     * @phpstan-return list<array{name: string, description: ?string}>
      */
     public function search($query, $mode = 0, $type = null);
 
diff --git a/src/Composer/Repository/Vcs/HgBitbucketDriver.php b/src/Composer/Repository/Vcs/HgBitbucketDriver.php
index 71505cf52..42adcb918 100644
--- a/src/Composer/Repository/Vcs/HgBitbucketDriver.php
+++ b/src/Composer/Repository/Vcs/HgBitbucketDriver.php
@@ -31,10 +31,12 @@ class HgBitbucketDriver extends BitbucketDriver
 
         if (null === $this->rootIdentifier) {
             if (!$this->getRepoData()) {
+                // @phpstan-ignore-next-line
                 if (!$this->fallbackDriver) {
                     throw new \LogicException('A fallback driver should be setup if getRepoData returns false');
                 }
 
+                // @phpstan-ignore-next-line
                 return $this->fallbackDriver->getRootIdentifier();
             }
 
diff --git a/src/Composer/Repository/Vcs/VcsDriver.php b/src/Composer/Repository/Vcs/VcsDriver.php
index 4e92658d7..8927a0dcc 100644
--- a/src/Composer/Repository/Vcs/VcsDriver.php
+++ b/src/Composer/Repository/Vcs/VcsDriver.php
@@ -45,7 +45,7 @@ abstract class VcsDriver implements VcsDriverInterface
     protected $httpDownloader;
     /** @var array */
     protected $infoCache = array();
-    /** @var Cache */
+    /** @var ?Cache */
     protected $cache;
 
     /**
diff --git a/src/Composer/Repository/VcsRepository.php b/src/Composer/Repository/VcsRepository.php
index 80d24f7a1..2456baaea 100644
--- a/src/Composer/Repository/VcsRepository.php
+++ b/src/Composer/Repository/VcsRepository.php
@@ -46,9 +46,9 @@ class VcsRepository extends ArrayRepository implements ConfigurableRepositoryInt
     protected $processExecutor;
     protected $branchErrorOccurred = false;
     private $drivers;
-    /** @var VcsDriverInterface */
+    /** @var ?VcsDriverInterface */
     private $driver;
-    /** @var VersionCacheInterface */
+    /** @var ?VersionCacheInterface */
     private $versionCache;
     private $emptyReferences = array();
     private $versionTransportExceptions = array();
diff --git a/src/Composer/Script/Event.php b/src/Composer/Script/Event.php
index 5ab431e75..af8bf55e7 100644
--- a/src/Composer/Script/Event.php
+++ b/src/Composer/Script/Event.php
@@ -95,7 +95,7 @@ class Event extends BaseEvent
     /**
      * Set the originating event.
      *
-     * @return \Composer\EventDispatcher\Event|null
+     * @return ?BaseEvent
      */
     public function getOriginatingEvent()
     {
@@ -105,7 +105,7 @@ class Event extends BaseEvent
     /**
      * Set the originating event.
      *
-     * @param  \Composer\EventDispatcher\Event $event
+     * @param  BaseEvent $event
      * @return $this
      */
     public function setOriginatingEvent(BaseEvent $event)
@@ -118,8 +118,8 @@ class Event extends BaseEvent
     /**
      * Returns the upper-most event in chain.
      *
-     * @param  \Composer\EventDispatcher\Event $event
-     * @return \Composer\EventDispatcher\Event
+     * @param  BaseEvent $event
+     * @return BaseEvent
      */
     private function calculateOriginatingEvent(BaseEvent $event)
     {
diff --git a/src/Composer/Util/AuthHelper.php b/src/Composer/Util/AuthHelper.php
index fa00e5bd6..abbc76cf7 100644
--- a/src/Composer/Util/AuthHelper.php
+++ b/src/Composer/Util/AuthHelper.php
@@ -210,7 +210,7 @@ class AuthHelper
                 if ($auth['password'] === 'oauth2') {
                     $headers[] = 'Authorization: Bearer '.$auth['username'];
                     $authenticationDisplayMessage = 'Using GitLab OAuth token authentication';
-                } elseif ($auth['password'] === 'private-token' || $auth['password'] === 'gitlab-ci-token') {
+                } else {
                     $headers[] = 'PRIVATE-TOKEN: '.$auth['username'];
                     $authenticationDisplayMessage = 'Using GitLab private token authentication';
                 }
diff --git a/src/Composer/Util/Bitbucket.php b/src/Composer/Util/Bitbucket.php
index 38611ac55..5970aa631 100644
--- a/src/Composer/Util/Bitbucket.php
+++ b/src/Composer/Util/Bitbucket.php
@@ -103,7 +103,12 @@ class Bitbucket
                 ),
             ));
 
-            $this->token = $response->decodeJson();
+            $token = $response->decodeJson();
+            if (!isset($token['expires_in']) || !isset($token['access_token'])) {
+                throw new \LogicException('Expected a token configured with expires_in and access_token present, got '.json_encode($token));
+            }
+
+            $this->token = $token;
         } catch (TransportException $e) {
             if ($e->getCode() === 400) {
                 $this->io->writeError('<error>Invalid OAuth consumer provided.</error>');
@@ -202,10 +207,12 @@ class Bitbucket
 
         $this->storeInAuthConfig($originUrl, $consumerKey, $consumerSecret);
 
-        if (!isset($this->token['expires_in']) || !isset($this->token['access_token'])) {
-            throw new \LogicException('Expected a token configured with expires_in and access_token present, got '.json_encode($this->token));
+        if (!isset($this->token['access_token'])) {
+            throw new \LogicException('Failed to initialize token above');
         }
 
+        // side effect above caused this, https://github.com/phpstan/phpstan/issues/5129
+        // @phpstan-ignore-next-line
         return $this->token['access_token'];
     }
 
@@ -219,8 +226,8 @@ class Bitbucket
     {
         $this->config->getConfigSource()->removeConfigSetting('bitbucket-oauth.'.$originUrl);
 
-        if (!isset($this->token['expires_in']) || !isset($this->token['access_token'])) {
-            throw new \LogicException('Expected a token configured with expires_in and access_token present, got '.json_encode($this->token));
+        if (null === $this->token || !isset($this->token['expires_in'])) {
+            throw new \LogicException('Expected a token configured with expires_in present, got '.json_encode($this->token));
         }
 
         $time = null === $this->time ? time() : $this->time;
diff --git a/src/Composer/Util/Filesystem.php b/src/Composer/Util/Filesystem.php
index 6b1da6a52..f1c8d38eb 100644
--- a/src/Composer/Util/Filesystem.php
+++ b/src/Composer/Util/Filesystem.php
@@ -24,7 +24,7 @@ use Symfony\Component\Finder\Finder;
  */
 class Filesystem
 {
-    /** @var ProcessExecutor */
+    /** @var ?ProcessExecutor */
     private $processExecutor;
 
     public function __construct(ProcessExecutor $executor = null)
diff --git a/src/Composer/Util/Http/CurlDownloader.php b/src/Composer/Util/Http/CurlDownloader.php
index 83c55f945..f511f17d3 100644
--- a/src/Composer/Util/Http/CurlDownloader.php
+++ b/src/Composer/Util/Http/CurlDownloader.php
@@ -466,7 +466,7 @@ class CurlDownloader
         // check for gitlab 404 when downloading archives
         if (
             $response->getStatusCode() === 404
-            && $this->config && in_array($job['origin'], $this->config->get('gitlab-domains'), true)
+            && in_array($job['origin'], $this->config->get('gitlab-domains'), true)
             && false !== strpos($job['url'], 'archive.zip')
         ) {
             $needsAuthRetry = 'GitLab requires authentication and it was not provided';
diff --git a/src/Composer/Util/Loop.php b/src/Composer/Util/Loop.php
index eb6461a33..00130a472 100644
--- a/src/Composer/Util/Loop.php
+++ b/src/Composer/Util/Loop.php
@@ -76,9 +76,7 @@ class Loop
 
         if ($progress) {
             $totalJobs = 0;
-            if ($this->httpDownloader) {
-                $totalJobs += $this->httpDownloader->countActiveJobs();
-            }
+            $totalJobs += $this->httpDownloader->countActiveJobs();
             if ($this->processExecutor) {
                 $totalJobs += $this->processExecutor->countActiveJobs();
             }
@@ -89,9 +87,7 @@ class Loop
         while (true) {
             $activeJobs = 0;
 
-            if ($this->httpDownloader) {
-                $activeJobs += $this->httpDownloader->countActiveJobs();
-            }
+            $activeJobs += $this->httpDownloader->countActiveJobs();
             if ($this->processExecutor) {
                 $activeJobs += $this->processExecutor->countActiveJobs();
             }
diff --git a/src/Composer/Util/Perforce.php b/src/Composer/Util/Perforce.php
index d399e4c78..1187b06c3 100644
--- a/src/Composer/Util/Perforce.php
+++ b/src/Composer/Util/Perforce.php
@@ -208,6 +208,8 @@ class Perforce
             return;
         }
         $this->p4User = $this->getP4variable('P4USER');
+        // https://github.com/phpstan/phpstan/issues/5129
+        // @phpstan-ignore-next-line
         if (strlen($this->p4User) > 0) {
             return;
         }
@@ -220,6 +222,10 @@ class Perforce
         $this->executeCommand($command);
     }
 
+    /**
+     * @param  string  $name
+     * @return ?string
+     */
     protected function getP4variable($name)
     {
         if ($this->windowsFlag) {
diff --git a/src/Composer/Util/RemoteFilesystem.php b/src/Composer/Util/RemoteFilesystem.php
index 9aed13ac2..8b16bb456 100644
--- a/src/Composer/Util/RemoteFilesystem.php
+++ b/src/Composer/Util/RemoteFilesystem.php
@@ -550,8 +550,8 @@ class RemoteFilesystem
                 // passing `null` to file_get_contents will convert `null` to `0` and return 0 bytes
                 $result = file_get_contents($fileUrl, false, $context);
             }
-        } catch (\Throwable $e) {
         } catch (\Exception $e) {
+        } catch (\Throwable $e) {
         }
 
         if ($maxFileSize !== null && Platform::strlen($result) >= $maxFileSize) {
diff --git a/src/Composer/Util/TlsHelper.php b/src/Composer/Util/TlsHelper.php
index cfe89870a..6fa70f0cc 100644
--- a/src/Composer/Util/TlsHelper.php
+++ b/src/Composer/Util/TlsHelper.php
@@ -162,7 +162,7 @@ final class TlsHelper
      *
      * @param string $certName CN/SAN
      *
-     * @return callable|void
+     * @return callable|null
      */
     private static function certNameMatcher($certName)
     {
@@ -180,14 +180,14 @@ final class TlsHelper
 
             if (3 > count($components)) {
                 // Must have 3+ components
-                return;
+                return null;
             }
 
             $firstComponent = $components[0];
 
             // Wildcard must be the last character.
             if ('*' !== $firstComponent[strlen($firstComponent) - 1]) {
-                return;
+                return null;
             }
 
             $wildcardRegex = preg_quote($certName);
@@ -198,5 +198,7 @@ final class TlsHelper
                 return 1 === preg_match($wildcardRegex, $hostname);
             };
         }
+
+        return null;
     }
 }
diff --git a/src/Composer/Util/Zip.php b/src/Composer/Util/Zip.php
index 2e4bc3774..7b1f6285c 100644
--- a/src/Composer/Util/Zip.php
+++ b/src/Composer/Util/Zip.php
@@ -42,11 +42,6 @@ class Zip
         }
 
         $foundFileIndex = self::locateFile($zip, 'composer.json');
-        if (false === $foundFileIndex) {
-            $zip->close();
-
-            return null;
-        }
 
         $content = null;
         $configurationFileName = $zip->getNameIndex($foundFileIndex);
diff --git a/tests/Composer/Test/InstallerTest.php b/tests/Composer/Test/InstallerTest.php
index 3ab4d6e39..3732941f0 100644
--- a/tests/Composer/Test/InstallerTest.php
+++ b/tests/Composer/Test/InstallerTest.php
@@ -82,6 +82,7 @@ class InstallerTest extends TestCase
         $installationManager = new InstallationManagerMock();
 
         // emulate a writable lock file
+        /** @var ?string $lockData */
         $lockData = null;
         $lockJsonMock = $this->getMockBuilder('Composer\Json\JsonFile')->disableOriginalConstructor()->getMock();
         $lockJsonMock->expects($this->any())
diff --git a/tests/Composer/Test/Platform/HhvmDetectorTest.php b/tests/Composer/Test/Platform/HhvmDetectorTest.php
index 68dc4a879..51926156c 100644
--- a/tests/Composer/Test/Platform/HhvmDetectorTest.php
+++ b/tests/Composer/Test/Platform/HhvmDetectorTest.php
@@ -32,8 +32,6 @@ class HhvmDetectorTest extends TestCase
     {
         if (!defined('HHVM_VERSION_ID')) {
             self::markTestSkipped('Not running with HHVM');
-
-            return;
         }
         $version = $this->hhvmDetector->getVersion();
         self::assertSame(self::versionIdToVersion(), $version);
@@ -43,18 +41,12 @@ class HhvmDetectorTest extends TestCase
     {
         if (defined('HHVM_VERSION_ID')) {
             self::markTestSkipped('Running with HHVM');
-
-            return;
         }
         if (PHP_VERSION_ID < 50400) {
             self::markTestSkipped('Test only works on PHP 5.4+');
-
-            return;
         }
         if (Platform::isWindows()) {
             self::markTestSkipped('Test does not run on Windows');
-
-            return;
         }
         $finder = new ExecutableFinder();
         $hhvm = $finder->find('hhvm');
diff --git a/tests/Composer/Test/Script/EventTest.php b/tests/Composer/Test/Script/EventTest.php
index b7c8cd9ff..6a4c3b678 100644
--- a/tests/Composer/Test/Script/EventTest.php
+++ b/tests/Composer/Test/Script/EventTest.php
@@ -35,6 +35,7 @@ class EventTest extends TestCase
 
         $scriptEvent->setOriginatingEvent($originatingEvent);
 
+        // @phpstan-ignore-next-line
         $this->assertSame(
             $originatingEvent,
             $scriptEvent->getOriginatingEvent(),
diff --git a/tests/Composer/Test/Util/ErrorHandlerTest.php b/tests/Composer/Test/Util/ErrorHandlerTest.php
index 89e97f653..551daaa25 100644
--- a/tests/Composer/Test/Util/ErrorHandlerTest.php
+++ b/tests/Composer/Test/Util/ErrorHandlerTest.php
@@ -57,6 +57,7 @@ class ErrorHandlerTest extends TestCase
             $this->setExpectedException('ErrorException', 'array_merge');
         }
 
+        // @phpstan-ignore-next-line
         array_merge(array(), 'string');
     }
 
diff --git a/tests/Composer/Test/Util/ZipTest.php b/tests/Composer/Test/Util/ZipTest.php
index 16fc5827d..32fff6a5c 100644
--- a/tests/Composer/Test/Util/ZipTest.php
+++ b/tests/Composer/Test/Util/ZipTest.php
@@ -35,8 +35,6 @@ class ZipTest extends TestCase
     {
         if (!extension_loaded('zip')) {
             $this->markTestSkipped('The PHP zip extension is not loaded.');
-
-            return;
         }
 
         $result = Zip::getComposerJson(__DIR__.'/Fixtures/Zip/invalid.zip');
@@ -48,8 +46,6 @@ class ZipTest extends TestCase
     {
         if (!extension_loaded('zip')) {
             $this->markTestSkipped('The PHP zip extension is not loaded.');
-
-            return;
         }
 
         $result = Zip::getComposerJson(__DIR__.'/Fixtures/Zip/empty.zip');
@@ -61,8 +57,6 @@ class ZipTest extends TestCase
     {
         if (!extension_loaded('zip')) {
             $this->markTestSkipped('The PHP zip extension is not loaded.');
-
-            return;
         }
 
         $this->setExpectedException('\RuntimeException', 'No composer.json found either at the top level or within the topmost directory');
@@ -74,8 +68,6 @@ class ZipTest extends TestCase
     {
         if (!extension_loaded('zip')) {
             $this->markTestSkipped('The PHP zip extension is not loaded.');
-
-            return;
         }
 
         $this->setExpectedException('\RuntimeException', 'No composer.json found either at the top level or within the topmost directory');
@@ -87,8 +79,6 @@ class ZipTest extends TestCase
     {
         if (!extension_loaded('zip')) {
             $this->markTestSkipped('The PHP zip extension is not loaded.');
-
-            return;
         }
 
         $result = Zip::getComposerJson(__DIR__.'/Fixtures/Zip/root.zip');
@@ -100,8 +90,6 @@ class ZipTest extends TestCase
     {
         if (!extension_loaded('zip')) {
             $this->markTestSkipped('The PHP zip extension is not loaded.');
-
-            return;
         }
 
         $result = Zip::getComposerJson(__DIR__.'/Fixtures/Zip/folder.zip');
@@ -112,8 +100,6 @@ class ZipTest extends TestCase
     {
         if (!extension_loaded('zip')) {
             $this->markTestSkipped('The PHP zip extension is not loaded.');
-
-            return;
         }
 
         $this->setExpectedException('\RuntimeException', 'Archive has more than one top level directories, and no composer.json was found on the top level, so it\'s an invalid archive. Top level paths found were: folder1/,folder2/');
@@ -125,8 +111,6 @@ class ZipTest extends TestCase
     {
         if (!extension_loaded('zip')) {
             $this->markTestSkipped('The PHP zip extension is not loaded.');
-
-            return;
         }
 
         $result = Zip::getComposerJson(__DIR__.'/Fixtures/Zip/single-sub.zip');