Fix target-dir update checks, fixes #2395

src/Composer/Installer/LibraryInstaller.php

@@ -160,9 +160,11 @@ class LibraryInstaller implements InstallerInterface
         $initialDownloadPath = $this->getInstallPath($initial);
         $targetDownloadPath = $this->getInstallPath($target);
         if ($targetDownloadPath !== $initialDownloadPath) {
-            // if the target is part of the initial dir, we force a remove + install
+            // if the target and initial dirs intersect, we force a remove + install
             // to avoid the rename wiping the target dir as part of the initial dir cleanup
-            if (strpos($initialDownloadPath, $targetDownloadPath) === 0) {
+            if (substr($initialDownloadPath, 0, strlen($targetDownloadPath)) === $targetDownloadPath
+                || substr($targetDownloadPath, 0, strlen($initialDownloadPath)) === $initialDownloadPath
+            ) {
                 $this->removeCode($initial);
                 $this->installCode($target);
 

tests/Composer/Test/Installer/LibraryInstallerTest.php

@@ -136,7 +136,7 @@ class LibraryInstallerTest extends TestCase
         $filesystem
           ->expects($this->once())
           ->method('rename')
-          ->with($this->vendorDir.'/package1', $this->vendorDir.'/package1/newtarget');
+          ->with($this->vendorDir.'/package1/oldtarget', $this->vendorDir.'/package1/newtarget');
 
         $initial = $this->createPackageMock();
         $target  = $this->createPackageMock();
@@ -146,6 +146,11 @@ class LibraryInstallerTest extends TestCase
             ->method('getPrettyName')
             ->will($this->returnValue('package1'));
 
+        $initial
+            ->expects($this->once())
+            ->method('getTargetDir')
+            ->will($this->returnValue('oldtarget'));
+
         $target
             ->expects($this->once())
             ->method('getPrettyName')