skip files with only known annotation names (#765)

Previously we would bail out early for files with no top level annotations, this also skips well known annotations (although it isn't perfect, and assumes people aren't shadowing these names).

Author: jakemac53

source_gen/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 3.0.0-wip
+
+- Update the GeneratorForAnnotation optimization to skip files with well known
+  annotation names such as `override`, `Deprecated`, and `pragma`.
+
 ## 3.0.0-dev
 
 - **Breaking Change**: use the new `element2` APIs in `analyzer`. Builders that

source_gen/lib/src/builder.dart

@@ -93,7 +93,7 @@ class _Builder extends Builder {
     if (!await resolver.isLibrary(buildStep.inputId)) return;
 
     if (_generators.every((g) => g is GeneratorForAnnotation) &&
-        !(await _hasAnyTopLevelAnnotations(
+        !(await _hasInterestingTopLevelAnnotations(
           buildStep.inputId,
           resolver,
           buildStep,
@@ -382,7 +382,7 @@ Stream<GeneratedOutput> _generate(
   }
 }
 
-Future<bool> _hasAnyTopLevelAnnotations(
+Future<bool> _hasInterestingTopLevelAnnotations(
   AssetId input,
   Resolver resolver,
   BuildStep buildStep,
@@ -399,16 +399,30 @@ Future<bool> _hasAnyTopLevelAnnotations(
     }
   }
   for (var declaration in parsed.declarations) {
-    if (declaration.metadata.isNotEmpty) return true;
+    if (declaration.metadata.any(_isUnknownAnnotation)) {
+      return true;
+    }
   }
   for (var partId in partIds) {
-    if (await _hasAnyTopLevelAnnotations(partId, resolver, buildStep)) {
+    if (await _hasInterestingTopLevelAnnotations(partId, resolver, buildStep)) {
       return true;
     }
   }
   return false;
 }
 
+bool _isUnknownAnnotation(Annotation annotation) {
+  const knownAnnotationNames = {
+    // Annotations from dart:core, there is an assumption that people are not
+    // overriding these.
+    'deprecated',
+    'Deprecated',
+    'override',
+    'pragma',
+  };
+  return !knownAnnotationNames.contains(annotation.name.name);
+}
+
 const defaultFileHeader = '// GENERATED CODE - DO NOT MODIFY BY HAND';
 
 String _defaultFormatOutput(String code, Version version) =>

source_gen/pubspec.yaml

@@ -1,5 +1,5 @@
 name: source_gen
-version: 3.0.0-dev
+version: 3.0.0-wip
 description: >-
   Source code generation builders and utilities for the Dart build system
 repository: https://github.com/dart-lang/source_gen/tree/master/source_gen

source_gen/test/builder_test.dart

@@ -889,7 +889,11 @@ foo generated content
     ''',
       testLibPartContent: '''
     part of 'test_lib.dart';
-    @deprecated
+
+    // Use this to avoid the short circuit.
+    const deprecated2 = deprecated;
+
+    @deprecated2
     int x;
     ''',
     );

source_gen/test/generator_for_annotation_test.dart

@@ -99,32 +99,37 @@ $dartFormatWidth
     }
   });
 
-  test(
-    'Does not resolve the library if there are no top level annotations',
-    () async {
-      final builder = LibraryBuilder(
-        _StubGenerator<Deprecated>('Deprecated', elementBehavior: (_) => null),
-      );
-      final input = AssetId('a', 'lib/a.dart');
-      final assets = {input: 'main() {}'};
-
-      final readerWriter =
-          TestReaderWriter()..testing.writeString(input, assets[input]!);
-
-      final resolver = _TestingResolver(assets);
-
-      await runBuilder(
-        builder,
-        [input],
-        readerWriter,
-        readerWriter,
-        _FixedResolvers(resolver),
-      );
+  test('Does not resolve the library if there are no interesting top level '
+      'annotations', () async {
+    final builder = LibraryBuilder(
+      _StubGenerator<Deprecated>('Deprecated', elementBehavior: (_) => null),
+    );
+    final input = AssetId('a', 'lib/a.dart');
+    final assets = {
+      input: '''
+@Deprecated()
+@deprecated
+@override
+@pragma('')
+main() {}''',
+    };
+
+    final readerWriter =
+        TestReaderWriter()..testing.writeString(input, assets[input]!);
+
+    final resolver = _TestingResolver(assets);
+
+    await runBuilder(
+      builder,
+      [input],
+      readerWriter,
+      readerWriter,
+      _FixedResolvers(resolver),
+    );
 
-      expect(resolver.parsedUnits, {input});
-      expect(resolver.resolvedLibs, isEmpty);
-    },
-  );
+    expect(resolver.parsedUnits, {input});
+    expect(resolver.resolvedLibs, isEmpty);
+  });
 
   test('applies to annotated libraries', () async {
     final builder = LibraryBuilder(
@@ -289,13 +294,16 @@ class _StubGenerator<T> extends GeneratorForAnnotation<T> {
 
 const _inputMap = {
   'a|lib/file.dart': '''
-     @deprecated
+     // Use this to avoid the short circuit.
+     const deprecated2 = deprecated;
+
+     @deprecated2
      final foo = 'foo';
 
-     @deprecated
+     @deprecated2
      final bar = 'bar';
 
-     @deprecated
+     @deprecated2
      final baz = 'baz';
      ''',
 };