Fail early if git/hg/svn can not be found on the system, so that download can be retried from dist, fixes #9681

src/Composer/Downloader/GitDownloader.php

@@ -71,6 +71,10 @@ class GitDownloader extends VcsDownloader implements DvcsDownloaderInterface
             if ($this->gitUtil->fetchRefOrSyncMirror($url, $cachePath, $ref) && is_dir($cachePath)) {
                 $this->cachedPackages[$package->getId()][$ref] = true;
             }
+        } else {
+            if (null === GitUtil::getVersion($this->process)) {
+                throw new \RuntimeException('git was not found in your PATH, skipping source download');
+            }
         }
     }
 

src/Composer/Downloader/HgDownloader.php

@@ -26,6 +26,9 @@ class HgDownloader extends VcsDownloader
      */
     protected function doDownload(PackageInterface $package, $path, $url, PackageInterface $prevPackage = null)
     {
+        if (null === HgUtils::getVersion($this->process)) {
+            throw new \RuntimeException('hg was not found in your PATH, skipping source download');
+        }
     }
 
     /**

src/Composer/Downloader/SvnDownloader.php

@@ -30,6 +30,11 @@ class SvnDownloader extends VcsDownloader
      */
     protected function doDownload(PackageInterface $package, $path, $url, PackageInterface $prevPackage = null)
     {
+        SvnUtil::cleanEnv();
+        $util = new SvnUtil($url, $this->io, $this->config, $this->process);
+        if (null === $util->binaryVersion()) {
+            throw new \RuntimeException('svn was not found in your PATH, skipping source download');
+        }
     }
 
     /**

src/Composer/Util/Git.php

@@ -403,15 +403,12 @@ class Git
     /**
      * Retrieves the current git version.
      *
-     * @return string|null The git version number.
+     * @return string|null The git version number, if present.
      */
     public static function getVersion(ProcessExecutor $process)
     {
         if (false === self::$version) {
             self::$version = null;
-            if (!$process) {
-                $process = new ProcessExecutor;
-            }
             if (0 === $process->execute('git --version', $output) && preg_match('/^git version (\d+(?:\.\d+)+)/m', $output, $matches)) {
                 self::$version = $matches[1];
             }

src/Composer/Util/Hg.php

@@ -74,10 +74,27 @@ class Hg
 
     private function throwException($message, $url)
     {
-        if (0 !== $this->process->execute('hg --version', $ignoredOutput)) {
+        if (null === self::getVersion($this->process)) {
             throw new \RuntimeException(Url::sanitize('Failed to clone ' . $url . ', hg was not found, check that it is installed and in your PATH env.' . "\n\n" . $this->process->getErrorOutput()));
         }
 
         throw new \RuntimeException(Url::sanitize($message));
     }
+
+    /**
+     * Retrieves the current hg version.
+     *
+     * @return string|null The hg version number, if present.
+     */
+    public static function getVersion(ProcessExecutor $process)
+    {
+        if (false === self::$version) {
+            self::$version = null;
+            if (0 === $this->process->execute('hg --version', $output) && preg_match('/version (\d+(?:\.\d+)+)/m', $output, $matches)) {
+                self::$version = $matches[1];
+            }
+        }
+
+        return self::$version;
+    }
 }