From 5dfd23668ed9d8e3e4aa88ae0eedae416a7f3732 Mon Sep 17 00:00:00 2001
From: Richard Heelin <richardh@channelgrabber.com>
Date: Mon, 17 Oct 2016 08:50:44 +0100
Subject: [PATCH] Only update the git repo if the commit we want doesn't exist,
 speeds up update from source

---
 src/Composer/Downloader/GitDownloader.php | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/Composer/Downloader/GitDownloader.php b/src/Composer/Downloader/GitDownloader.php
index 02ea7928a..5acc5fed6 100644
--- a/src/Composer/Downloader/GitDownloader.php
+++ b/src/Composer/Downloader/GitDownloader.php
@@ -105,10 +105,10 @@ class GitDownloader extends VcsDownloader implements DvcsDownloaderInterface
 
         $ref = $target->getSourceReference();
         $this->io->writeError("    Checking out ".$ref);
-        $command = 'git remote set-url composer %s && git fetch composer && git fetch --tags composer';
+        $command = 'git remote set-url composer %s && git rev-parse --quiet --verify %s^{commit} || (git fetch composer && git fetch --tags composer)';
 
-        $commandCallable = function ($url) use ($command) {
-            return sprintf($command, ProcessExecutor::escape($url));
+        $commandCallable = function ($url) use ($command, $ref) {
+            return sprintf($command, ProcessExecutor::escape($url), ProcessExecutor::escape($ref));
         };
 
         $this->gitUtil->runCommand($commandCallable, $url, $path);