Add annotations to libraries

CHANGELOG.md

@@ -3,6 +3,7 @@
 * Add `Expression.spread` for the spread operator `...`.
 * Add support 'late' field modifier.
 * Add support for `Expression.nullChecked` to add a null assertion operator.
+* A `Library` can now be annotated.
 
 ## 4.0.0
 

lib/src/emitter.dart

@@ -354,6 +354,13 @@ class DartEmitter extends Object
       }
     }
 
+    if (spec.name != null) {
+      spec.annotations.forEach((a) => visitAnnotation(a, output));
+      output.write('library ${spec.name!};');
+    } else if (spec.annotations.isNotEmpty) {
+      throw StateError('a library name is required for annotations');
+    }
+
     final directives = <Directive>[...allocator.imports, ...spec.directives];
 
     if (orderDirectives) {

lib/src/specs/library.dart

@@ -7,19 +7,31 @@ import 'package:built_value/built_value.dart';
 import 'package:meta/meta.dart';
 
 import '../base.dart';
+import '../mixins/annotations.dart';
 import '../visitors.dart';
 import 'directive.dart';
+import 'expression.dart';
 
 part 'library.g.dart';
 
 @immutable
-abstract class Library implements Built<Library, LibraryBuilder>, Spec {
+abstract class Library
+    with HasAnnotations
+    implements Built<Library, LibraryBuilder>, Spec {
   factory Library([void Function(LibraryBuilder) updates]) = _$Library;
   Library._();
 
+  @override
+  BuiltList<Expression> get annotations;
+
   BuiltList<Directive> get directives;
   BuiltList<Spec> get body;
 
+  /// Name of the library.
+  /// 
+  /// May be `null` when no [annotations] are specified.
+  String? get name;
+
   @override
   R accept<R>(
     SpecVisitor<R> visitor, [
@@ -28,10 +40,17 @@ abstract class Library implements Built<Library, LibraryBuilder>, Spec {
       visitor.visitLibrary(this, context);
 }
 
-abstract class LibraryBuilder implements Builder<Library, LibraryBuilder> {
+abstract class LibraryBuilder
+    with HasAnnotationsBuilder
+    implements Builder<Library, LibraryBuilder> {
   factory LibraryBuilder() = _$LibraryBuilder;
   LibraryBuilder._();
 
+  @override
+  ListBuilder<Expression> annotations = ListBuilder<Expression>();
+
   ListBuilder<Spec> body = ListBuilder<Spec>();
   ListBuilder<Directive> directives = ListBuilder<Directive>();
+
+  String? name;
 }

test/specs/library_test.dart

@@ -137,5 +137,36 @@ void main() {
           ''', DartEmitter()),
       );
     });
+
+    test('should emit a source file with annotations', () {
+      expect(
+        Library(
+          (b) => b
+            ..name = 'js_interop'
+            ..annotations.add(
+              refer('JS', 'package:js/js.dart').call([]),
+            ),
+        ),
+        equalsDart(r'''
+          @JS()
+          library js_interop;
+          import 'package:js/js.dart';
+        ''', DartEmitter(allocator: Allocator())),
+      );
+    });
+
+    test('should error on unnamed library with annotations', () {
+      expect(
+        () {
+          Library(
+            (b) => b
+              ..annotations.add(
+                refer('JS', 'package:js/js.dart').call([]),
+              ),
+          ).accept(DartEmitter());
+        },
+        throwsStateError,
+      );
+    });
   });
 }