Add option allow-empty-diff for diff command

.gitignore

@@ -11,3 +11,5 @@ phpunit.xml
 /.phpcs-cache
 /box.phar
 /box.json
+
+# Please don't add your IDE's files here, use global gitignore instead.

lib/Doctrine/Migrations/Tools/Console/Command/DiffCommand.php

@@ -5,6 +5,7 @@
 namespace Doctrine\Migrations\Tools\Console\Command;
 
 use Doctrine\Migrations\Generator\DiffGenerator;
+use Doctrine\Migrations\Generator\Exception\NoChangesDetected;
 use Doctrine\Migrations\Provider\OrmSchemaProvider;
 use Doctrine\Migrations\Provider\SchemaProviderInterface;
 use Doctrine\Migrations\Tools\Console\Exception\InvalidOptionUsage;
@@ -83,6 +84,12 @@ protected function configure() : void
                 InputOption::VALUE_OPTIONAL,
                 'Check Database Platform to the generated code.',
                 true
+            )
+            ->addOption(
+                'allow-empty-diff',
+                null,
+                InputOption::VALUE_NONE,
+                'Do not throw an exception when no changes are detected.'
             );
     }
 
@@ -96,6 +103,7 @@ public function execute(
         $filterExpression = $input->getOption('filter-expression') ?? null;
         $formatted        = (bool) $input->getOption('formatted');
         $lineLength       = (int) $input->getOption('line-length');
+        $allowEmptyDiff   = (bool) $input->getOption('allow-empty-diff');
         $checkDbPlatform  = filter_var($input->getOption('check-database-platform'), FILTER_VALIDATE_BOOLEAN);
 
         if ($formatted) {
@@ -108,13 +116,22 @@ public function execute(
 
         $versionNumber = $this->configuration->generateVersionNumber();
 
-        $path = $this->createMigrationDiffGenerator()->generate(
-            $versionNumber,
-            $filterExpression,
-            $formatted,
-            $lineLength,
-            $checkDbPlatform
-        );
+        try {
+            $path = $this->createMigrationDiffGenerator()->generate(
+                $versionNumber,
+                $filterExpression,
+                $formatted,
+                $lineLength,
+                $checkDbPlatform
+            );
+        } catch (NoChangesDetected $exception) {
+            if ($allowEmptyDiff) {
+                $output->writeln($exception->getMessage());
+
+                return 0;
+            }
+            throw $exception;
+        }
 
         $editorCommand = $input->getOption('editor-cmd');
 

lib/Doctrine/Migrations/Tools/Console/Command/MigrateCommand.php

@@ -61,7 +61,7 @@ protected function configure() : void
                 'allow-no-migration',
                 null,
                 InputOption::VALUE_NONE,
-                'Don\'t throw an exception if no migration is available (CI).'
+                'Do not throw an exception if no migration is available.'
             )
             ->addOption(
                 'all-or-nothing',

tests/Doctrine/Migrations/Tests/Tools/Console/Command/DiffCommandTest.php

@@ -49,10 +49,15 @@ public function testExecute() : void
 
         $input->expects(self::at(3))
             ->method('getOption')
-            ->with('check-database-platform')
+            ->with('allow-empty-diff')
             ->willReturn(true);
 
         $input->expects(self::at(4))
+            ->method('getOption')
+            ->with('check-database-platform')
+            ->willReturn(true);
+
+        $input->expects(self::at(5))
             ->method('getOption')
             ->with('editor-cmd')
             ->willReturn('mate');