feat: add support for custom output formatting

lib/src/generate_for_element.dart

@@ -17,8 +17,9 @@ final _testAnnotationWarnings = <String>{};
 Future<String> generateForElement<T>(
   GeneratorForAnnotation<T> generator,
   LibraryReader libraryReader,
-  String name,
-) async {
+  String name, {
+  String Function(String code)? formatOutput,
+}) async {
   final elements =
       libraryReader.allElements.where((e) => e.name3 == name).toList();
 
@@ -93,11 +94,11 @@ Future<String> generateForElement<T>(
 
   final generated = await generatedStream.join('\n\n');
 
-  final formatter = dart_style.DartFormatter(
+  formatOutput ??= dart_style.DartFormatter(
     languageVersion: libraryReader.element.languageVersion.effective,
-  );
+  ).format;
 
-  return formatter.format(generated);
+  return formatOutput(generated);
 }
 
 class _MockBuildStep extends BuildStep {

lib/src/test_annotated_classes.dart

@@ -33,13 +33,15 @@ void testAnnotatedElements<T>(
   Map<String, GeneratorForAnnotation<T>>? additionalGenerators,
   Iterable<String>? expectedAnnotatedTests,
   Iterable<String>? defaultConfiguration,
+  String Function(String code)? formatOutput,
 }) {
   for (var entry in getAnnotatedClasses<T>(
     libraryReader,
     defaultGenerator,
     additionalGenerators: additionalGenerators,
     expectedAnnotatedTests: expectedAnnotatedTests,
     defaultConfiguration: defaultConfiguration,
+    formatOutput: formatOutput,
   )) {
     entry._registerTest();
   }
@@ -54,6 +56,7 @@ List<AnnotatedTest<T>> getAnnotatedClasses<T>(
   Map<String, GeneratorForAnnotation<T>>? additionalGenerators,
   Iterable<String>? expectedAnnotatedTests,
   Iterable<String>? defaultConfiguration,
+  String Function(String code)? formatOutput,
 }) {
   final generators = <String, GeneratorForAnnotation<T>>{
     _defaultConfigurationName: defaultGenerator,
@@ -181,6 +184,7 @@ List<AnnotatedTest<T>> getAnnotatedClasses<T>(
           configuration,
           entry.elementName,
           entry.expectation,
+          formatOutput: formatOutput,
         ),
       );
     }
@@ -216,6 +220,7 @@ class AnnotatedTest<T> {
   final LibraryReader _libraryReader;
   final TestExpectation expectation;
   final String _elementName;
+  final String Function(String code)? _formatOutput;
 
   String get _testName {
     var value = _elementName;
@@ -230,8 +235,9 @@ class AnnotatedTest<T> {
     this.generator,
     this.configuration,
     this._elementName,
-    this.expectation,
-  );
+    this.expectation, {
+    String Function(String code)? formatOutput,
+  }) : _formatOutput = formatOutput;
 
   void _registerTest() {
     if (expectation is ShouldGenerate) {
@@ -247,8 +253,12 @@ class AnnotatedTest<T> {
     throw StateError('Should never get here.');
   }
 
-  Future<String> _generate() =>
-      generateForElement<T>(generator, _libraryReader, _elementName);
+  Future<String> _generate() => generateForElement<T>(
+        generator,
+        _libraryReader,
+        _elementName,
+        formatOutput: _formatOutput,
+      );
 
   Future<void> _shouldGenerateTest() async {
     final output = await _generate();

test/generate_for_element_test.dart

@@ -92,6 +92,75 @@ const TestClass2NameLength = 10;
 const TestClass2NameLowerCase = 'testclass2';
 ''');
     });
+
+    group(
+      'formatOutput',
+      () {
+        test(
+          'should format the generated source code with `DartFormatter` when `formatOutput` is `null`.',
+          () async {
+            final output = await generateForElement(
+              const TestGenerator(),
+              reader,
+              'TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANop',
+              formatOutput: null,
+            );
+            printOnFailure(output);
+            expect(
+              output,
+              r'''
+const TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANopNameLength =
+    68;
+
+const TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANopNameLowerCase =
+    testclassthathasaverylongnamethatshouldnotwrapwhenformatoutputisanop;
+''',
+            );
+          },
+        );
+
+        test(
+          'should not format the generated source code when `formatOutput` is a NOP.',
+          () async {
+            final output = await generateForElement(
+              const TestGenerator(),
+              reader,
+              'TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANop',
+              formatOutput: (code) => code,
+            );
+            printOnFailure(output);
+            expect(
+              output,
+              r'''
+const TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANopNameLength = 68;
+
+const TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANopNameLowerCase = testclassthathasaverylongnamethatshouldnotwrapwhenformatoutputisanop;''',
+            );
+          },
+        );
+
+        test(
+          'should format the generated source code with a custom formatter when `formatOutput` is a custom formatter.',
+          () async {
+            final output = await generateForElement(
+              const TestGenerator(),
+              reader,
+              'TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANop',
+              formatOutput: (code) => '$code\n',
+            );
+            printOnFailure(output);
+            expect(
+              output,
+              r'''
+const TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANopNameLength = 68;
+
+const TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANopNameLowerCase = testclassthathasaverylongnamethatshouldnotwrapwhenformatoutputisanop;
+''',
+            );
+          },
+        );
+      },
+    );
   });
 
   test('throwsInvalidGenerationSourceError', () async {

test/init_library_reader_test.dart

@@ -29,6 +29,7 @@ void main() {
           'class TestClassWithBadMember',
           'int badTestFunc()',
           'int badTestField',
+          'class TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANop',
           'class TestClass2',
         ]),
       );

test/src/test_library.dart

@@ -89,3 +89,6 @@ int badTestFunc() => 42;
 @ShouldThrow('Uh...', configurations: ['vague'], element: false)
 @TestAnnotation()
 const badTestField = 42;
+
+@TestAnnotation()
+class TestClassThatHasAVeryLongNameThatShouldNotWrapWhenFormatOutputIsANop {}