Add --no-checkout flag to avoid checking out the default branch first, fixes #2717

src/Composer/Downloader/GitDownloader.php

@@ -33,7 +33,7 @@ class GitDownloader extends VcsDownloader
 
         $ref = $package->getSourceReference();
         $flag = defined('PHP_WINDOWS_VERSION_MAJOR') ? '/D ' : '';
-        $command = 'git clone %s %s && cd '.$flag.'%2$s && git remote add composer %1$s && git fetch composer';
+        $command = 'git clone --no-checkout %s %s && cd '.$flag.'%2$s && git remote add composer %1$s && git fetch composer';
         $this->io->write("    Cloning ".$ref);
 
         $commandCallable = function($url) use ($ref, $path, $command) {

tests/Composer/Test/Downloader/GitDownloaderTest.php

@@ -58,7 +58,7 @@ class GitDownloaderTest extends \PHPUnit_Framework_TestCase
             ->will($this->returnValue('dev-master'));
         $processExecutor = $this->getMock('Composer\Util\ProcessExecutor');
 
-        $expectedGitCommand = $this->winCompat("git clone 'https://example.com/composer/composer' 'composerPath' && cd 'composerPath' && git remote add composer 'https://example.com/composer/composer' && git fetch composer");
+        $expectedGitCommand = $this->winCompat("git clone --no-checkout 'https://example.com/composer/composer' 'composerPath' && cd 'composerPath' && git remote add composer 'https://example.com/composer/composer' && git fetch composer");
         $processExecutor->expects($this->at(0))
             ->method('execute')
             ->with($this->equalTo($expectedGitCommand))
@@ -97,13 +97,13 @@ class GitDownloaderTest extends \PHPUnit_Framework_TestCase
             ->will($this->returnValue('1.0.0'));
         $processExecutor = $this->getMock('Composer\Util\ProcessExecutor');
 
-        $expectedGitCommand = $this->winCompat("git clone 'git://github.com/composer/composer' 'composerPath' && cd 'composerPath' && git remote add composer 'git://github.com/composer/composer' && git fetch composer");
+        $expectedGitCommand = $this->winCompat("git clone --no-checkout 'git://github.com/composer/composer' 'composerPath' && cd 'composerPath' && git remote add composer 'git://github.com/composer/composer' && git fetch composer");
         $processExecutor->expects($this->at(0))
             ->method('execute')
             ->with($this->equalTo($expectedGitCommand))
             ->will($this->returnValue(1));
 
-        $expectedGitCommand = $this->winCompat("git clone 'https://github.com/composer/composer' 'composerPath' && cd 'composerPath' && git remote add composer 'https://github.com/composer/composer' && git fetch composer");
+        $expectedGitCommand = $this->winCompat("git clone --no-checkout 'https://github.com/composer/composer' 'composerPath' && cd 'composerPath' && git remote add composer 'https://github.com/composer/composer' && git fetch composer");
         $processExecutor->expects($this->at(2))
             ->method('execute')
             ->with($this->equalTo($expectedGitCommand))
@@ -154,7 +154,7 @@ class GitDownloaderTest extends \PHPUnit_Framework_TestCase
             ->will($this->returnValue('1.0.0'));
         $processExecutor = $this->getMock('Composer\Util\ProcessExecutor');
 
-        $expectedGitCommand = $this->winCompat("git clone '{$protocol}://github.com/composer/composer' 'composerPath' && cd 'composerPath' && git remote add composer '{$protocol}://github.com/composer/composer' && git fetch composer");
+        $expectedGitCommand = $this->winCompat("git clone --no-checkout '{$protocol}://github.com/composer/composer' 'composerPath' && cd 'composerPath' && git remote add composer '{$protocol}://github.com/composer/composer' && git fetch composer");
         $processExecutor->expects($this->at(0))
             ->method('execute')
             ->with($this->equalTo($expectedGitCommand))
@@ -182,7 +182,7 @@ class GitDownloaderTest extends \PHPUnit_Framework_TestCase
      */
     public function testDownloadThrowsRuntimeExceptionIfGitCommandFails()
     {
-        $expectedGitCommand = $this->winCompat("git clone 'https://example.com/composer/composer' 'composerPath' && cd 'composerPath' && git remote add composer 'https://example.com/composer/composer' && git fetch composer");
+        $expectedGitCommand = $this->winCompat("git clone --no-checkout 'https://example.com/composer/composer' 'composerPath' && cd 'composerPath' && git remote add composer 'https://example.com/composer/composer' && git fetch composer");
         $packageMock = $this->getMock('Composer\Package\PackageInterface');
         $packageMock->expects($this->any())
             ->method('getSourceReference')