feat: support diffing against empty composer.lock files

Author: wikando-ck

README.md

@@ -83,6 +83,7 @@ composer diff --help # Display detailed usage instructions
 ```shell script
 composer diff master # Compare current composer.lock with the one on master branch
 composer diff master:composer.lock develop:composer.lock -p # Compare master and develop branches, including platform dependencies
+composer diff /path/to/empty/composer.lock composer.lock # Compare a new lock file against an empty base
 composer diff --no-dev # ignore dev dependencies
 composer diff -p # include platform dependencies
 composer diff -f json # Output as JSON instead of table

src/PackageDiff.php

@@ -210,7 +210,7 @@ private function getFileContents($path, $lockFile = true)
 
         if (filter_var($localPath, FILTER_VALIDATE_URL, FILTER_FLAG_PATH_REQUIRED) || file_exists($localPath)) {
             // @phpstan-ignore return.type
-            return file_get_contents($localPath);
+            return $this->normalizeFileContents(file_get_contents($localPath));
         }
 
         if (false === strpos($originalPath, self::GIT_SEPARATOR)) {
@@ -234,7 +234,21 @@ private function getFileContents($path, $lockFile = true)
             return '{}'; // Do not throw exception for composer.json as it might not exist and that's fine
         }
 
-        return $outputString;
+        return $this->normalizeFileContents($outputString);
+    }
+
+    /**
+     * @param string $contents
+     *
+     * @return string
+     */
+    private function normalizeFileContents($contents)
+    {
+        if ('' === trim($contents)) {
+            return '{}';
+        }
+
+        return $contents;
     }
 
     /**

tests/PackageDiffTest.php

@@ -152,6 +152,31 @@ public function testLoadFromEmptyArray()
         $this->assertInstanceOf('Composer\Repository\ArrayRepository', $diff->loadPackagesFromArray(array(), true, true));
     }
 
+    public function testDiffAgainstEmptyBaseLockFile()
+    {
+        $diff = new PackageDiff();
+
+        $prodOperations = $diff->getPackageDiff(
+            __DIR__.'/fixtures/empty/composer.lock',
+            __DIR__.'/fixtures/empty-target/composer.lock',
+            false,
+            false
+        );
+        $devOperations = $diff->getPackageDiff(
+            __DIR__.'/fixtures/empty/composer.lock',
+            __DIR__.'/fixtures/empty-target/composer.lock',
+            true,
+            false
+        );
+
+        $this->assertSame(array(
+            'install example/package 1.2.3',
+        ), array_map(array($this, 'entryToString'), $prodOperations->getArrayCopy()));
+        $this->assertSame(array(
+            'install example/dev-package 2.3.4',
+        ), array_map(array($this, 'entryToString'), $devOperations->getArrayCopy()));
+    }
+
     public function diffOperationsProvider()
     {
         return array(