bug #1039 Do not synchronize package.json if symfony/flex is not installed (leofeyer)

This PR was submitted for the 2.x branch but it was merged into the 1.x branch instead.

Discussion
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Do not synchronize package.json if symfony/flex is not installed

Just as the project is not configured and no recipes are loaded if symfony/flex is not in the root `composer.json`, the `package.json` should not be synchronized in this case.

Commits
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740bc2f Do not synchronize package.json if symfony/flex is not installed

Author: fabpot

src/Flex.php

@@ -600,6 +600,12 @@ public function finish(string $rootDir, ?string $originalComposerJsonHash = null
 
     private function synchronizePackageJson(string $rootDir)
     {
+        if (!$this->downloader->isEnabled()) {
+            $this->io->writeError('<warning>Synchronizing package.json is disabled: "symfony/flex" not found in the root composer.json</>');
+
+            return;
+        }
+
         $rootDir = realpath($rootDir);
         $vendorDir = trim((new Filesystem())->makePathRelative($this->config->get('vendor-dir'), $rootDir), '/');