bug #978 [Bug] Fix Flex not installing recipes while it is being upgraded (weaverryan)

This PR was squashed before being merged into the 1.x branch.

Discussion
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[Bug] Fix Flex not installing recipes while it is being upgraded

Fixes #977

Here's the lifecycle:

A) Packages are installed/updated and `Flex::recordOperations()` is called.
B) Composer sees that `symfony/flex` is updated and unloads the plugin and reloads it under a new `Symfony\Flex\Flex_composer_tmp0` class. This results in the `Flex::$operations` property being lost.
C) And so, no recipes are installed.

This PR "stashes" the operations directly on `Symfony/Flex/Flex` where we then read them later. Tested locally. Amazing, it seems to work perfectly.

Also, backports #976 to 1.x - my fault for making the PR on the wrong branch.

Cheers!

Commits
-------

62f7874 [Bug] Fix Flex not installing recipes while it is being upgraded

Author: fabpot

src/Flex.php

@@ -60,6 +60,8 @@
  */
 class Flex implements PluginInterface, EventSubscriberInterface
 {
+    public static $storedOperations = [];
+
     /**
      * @var Composer
      */
@@ -129,6 +131,13 @@ class_exists(__NAMESPACE__.str_replace('/', '\\', substr($file, \strlen(__DIR__)
         $this->config = $composer->getConfig();
         $this->options = $this->initOptions();
 
+        // if Flex is being upgraded, the original operations from the original Flex
+        // instance are stored in the static property, so we can reuse them now.
+        if (property_exists(self::class, 'storedOperations') && self::$storedOperations) {
+            $this->operations = self::$storedOperations;
+            self::$storedOperations = [];
+        }
+
         $symfonyRequire = preg_replace('/\.x$/', '.x-dev', getenv('SYMFONY_REQUIRE') ?: ($composer->getPackage()->getExtra()['symfony']['require'] ?? ''));
 
         if ($composer2 = version_compare('2.0.0', PluginInterface::PLUGIN_API_VERSION, '<=')) {
@@ -299,6 +308,8 @@ class_exists(__NAMESPACE__.str_replace('/', '\\', substr($file, \strlen(__DIR__)
      */
     public function deactivate(Composer $composer, IOInterface $io)
     {
+        // store operations in case Flex is being upgraded
+        self::$storedOperations = $this->operations;
         self::$activated = false;
     }
 
@@ -550,10 +561,12 @@ function ($value) {
             }
         }
 
-        foreach ($postInstallRecipes as $recipe) {
-            $this->configurator->postInstall($recipe, $this->lock, [
-                'force' => $event instanceof UpdateEvent && $event->force(),
-            ]);
+        if (method_exists($this->configurator, 'postInstall')) {
+            foreach ($postInstallRecipes as $recipe) {
+                $this->configurator->postInstall($recipe, $this->lock, [
+                    'force' => $event instanceof UpdateEvent && $event->force(),
+                ]);
+            }
         }
 
         if (null !== $manifest) {