Add --2.2 flag to self-update for 2.2 LTS as well as EOL marker support

src/Composer/Command/SelfUpdateCommand.php

@@ -59,6 +59,7 @@ class SelfUpdateCommand extends BaseCommand
                 new InputOption('snapshot', null, InputOption::VALUE_NONE, 'Force an update to the snapshot channel'),
                 new InputOption('1', null, InputOption::VALUE_NONE, 'Force an update to the stable channel, but only use 1.x versions'),
                 new InputOption('2', null, InputOption::VALUE_NONE, 'Force an update to the stable channel, but only use 2.x versions'),
+                new InputOption('2.2', null, InputOption::VALUE_NONE, 'Force an update to the stable channel, but only use 2.2.x LTS versions'),
                 new InputOption('set-channel-only', null, InputOption::VALUE_NONE, 'Only store the channel as the default one and then exit'),
             ))
             ->setHelp(
@@ -182,8 +183,12 @@ EOT
             }
         }
 
-        if ($requestedChannel && is_numeric($requestedChannel) && strpos($latestStable['version'], $requestedChannel) !== 0) {
-            $io->writeError('<warning>Warning: You forced the install of '.$latestVersion.' via --'.$requestedChannel.', but '.$latestStable['version'].' is the latest stable version. Updating to it via composer self-update --stable is recommended.</warning>');
+        $effectiveChannel = $requestedChannel === null ? $versionsUtil->getChannel() : $requestedChannel;
+        if (is_numeric($effectiveChannel) && strpos($latestStable['version'], $effectiveChannel) !== 0) {
+            $io->writeError('<warning>Warning: You forced the install of '.$latestVersion.' via --'.$effectiveChannel.', but '.$latestStable['version'].' is the latest stable version. Updating to it via composer self-update --stable is recommended.</warning>');
+        }
+        if (isset($latest['eol'])) {
+            $io->writeError('<warning>Warning: Version '.$latestVersion.' is EOL / End of Life. '.$latestStable['version'].' is the latest stable version. Updating to it via composer self-update --stable is recommended.</warning>');
         }
 
         if (Preg::isMatch('{^[0-9a-f]{40}$}', $updateVersion) && $updateVersion !== $latestVersion) {

src/Composer/SelfUpdate/Versions.php

@@ -12,6 +12,7 @@
 
 namespace Composer\SelfUpdate;
 
+use Composer\Pcre\Preg;
 use Composer\Util\HttpDownloader;
 use Composer\Config;
 
@@ -21,7 +22,7 @@ use Composer\Config;
 class Versions
 {
     /** @var string[] */
-    public static $channels = array('stable', 'preview', 'snapshot', '1', '2');
+    public static $channels = array('stable', 'preview', 'snapshot', '1', '2', '2.2');
 
     /** @var HttpDownloader */
     private $httpDownloader;
@@ -29,7 +30,7 @@ class Versions
     private $config;
     /** @var string */
     private $channel;
-    /** @var array<string, array<int, array{path: string, version: string, min-php: int}>> */
+    /** @var array<string, array<int, array{path: string, version: string, min-php: int, eol?: true}>> */
     private $versionsData;
 
     public function __construct(Config $config, HttpDownloader $httpDownloader)
@@ -50,7 +51,7 @@ class Versions
         $channelFile = $this->config->get('home').'/update-channel';
         if (file_exists($channelFile)) {
             $channel = trim(file_get_contents($channelFile));
-            if (in_array($channel, array('stable', 'preview', 'snapshot'), true)) {
+            if (in_array($channel, array('stable', 'preview', 'snapshot', '2.2'), true)) {
                 return $this->channel = $channel;
             }
         }
@@ -71,13 +72,14 @@ class Versions
 
         $channelFile = $this->config->get('home').'/update-channel';
         $this->channel = $channel;
-        file_put_contents($channelFile, (is_numeric($channel) ? 'stable' : $channel).PHP_EOL);
+        // rewrite '2' and '1' channels to stable for future self-updates, but LTS ones like '2.2' remain pinned
+        file_put_contents($channelFile, (Preg::isMatch('{^\d+$}D', $channel) ? 'stable' : $channel).PHP_EOL);
     }
 
     /**
      * @param string|null $channel
      *
-     * @return array{path: string, version: string, min-php: int}
+     * @return array{path: string, version: string, min-php: int, eol?: true}
      */
     public function getLatest($channel = null)
     {
@@ -93,7 +95,7 @@ class Versions
     }
 
     /**
-     * @return array<string, array<int, array{path: string, version: string, min-php: int}>>
+     * @return array<string, array<int, array{path: string, version: string, min-php: int, eol?: true}>>
      */
     private function getVersionsData()
     {