Add typeNameOf(DartType). (dart-lang/source_gen#295)

* Add typeNameOf(DartType).

* Dartfmt.

source_gen/source_gen/CHANGELOG.md

@@ -1,5 +1,9 @@
 ## 0.7.4-dev
 
+* Added `typeNameOf`, which is a safe way to get the name of a `DartType`,
+  even when the type is a `FunctionType`, which has a `null` name in newer
+  versions of the Dart analyzer.
+
 * Added `LibraryReader.pathToUrl(Uri|String)`, which computes the `import` or
   `export` path necessary to reach the provided URL from the current library.
   Also added `pathToAsset` and `pathToElement` as convenience functions.

source_gen/source_gen/lib/source_gen.dart

@@ -12,3 +12,4 @@ export 'src/generator_for_annotation.dart';
 export 'src/library.dart' show AnnotatedElement, LibraryReader;
 export 'src/span_for_element.dart' show spanForElement;
 export 'src/type_checker.dart' show TypeChecker;
+export 'src/utils.dart' show typeNameOf;

source_gen/source_gen/lib/src/utils.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/dart/element/type.dart';
 import 'package:build/build.dart';
 import 'package:path/path.dart' as p;
 
@@ -39,6 +40,26 @@ String friendlyNameForElement(Element element) {
   return names.join(' ');
 }
 
+/// Returns a non-null name for the provided [type].
+///
+/// In newer versions of the Dart analyzer, a `typedef` does not keep the
+/// existing `name`, because it is used an alias:
+/// ```
+/// // Used to return `VoidFunc` for name, is now `null`.
+/// typedef VoidFunc = void Function();
+/// ```
+///
+/// This function will return `'VoidFunc'`, unlike [DartType.name].
+String typeNameOf(DartType type) {
+  if (type is FunctionType) {
+    final element = type.element;
+    if (element is GenericFunctionTypeElement) {
+      return element.enclosingElement.name;
+    }
+  }
+  return type.name;
+}
+
 /// Returns a name suitable for `part of "..."` when pointing to [element].
 ///
 /// Returns `null` if [element] is missing identifier.

source_gen/source_gen/test/utils_test.dart

@@ -0,0 +1,43 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Increase timeouts on this test which resolves source code and can be slow.
+@Timeout.factor(2.0)
+import 'package:analyzer/dart/element/element.dart';
+import 'package:build_test/build_test.dart';
+import 'package:source_gen/source_gen.dart';
+import 'package:test/test.dart';
+
+void main() {
+  ClassElement example;
+
+  setUpAll(() async {
+    const source = r'''
+      library example;
+
+      abstract class Example {
+        ClassType classType();
+        FunctionType functionType();
+      }
+
+      class ClassType {}
+      typedef FunctionType();
+    ''';
+    example = await resolveSource(
+        source,
+        (resolver) => resolver
+            .findLibraryByName('example')
+            .then((e) => e.getType('Example')));
+  });
+
+  test('should return the name of a class type', () {
+    final classType = example.methods.first.returnType;
+    expect(typeNameOf(classType), 'ClassType');
+  });
+
+  test('should return the name of a function type', () {
+    final functionType = example.methods.last.returnType;
+    expect(typeNameOf(functionType), 'FunctionType');
+  });
+}