use Analyzer's computed constants instead of pattern matching the annotation AST

lib/src/utils.dart

 // Copyright (c) 2015, 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.
 
 /// Holds a couple utility functions used at various places in the system.
 library dev_compiler.src.utils;
 
 import 'dart:io';
 
 import 'package:path/path.dart' as path;
 import 'package:analyzer/src/generated/ast.dart'
     show
         ImportDirective,
         ExportDirective,
         PartDirective,
         CompilationUnit,
         Identifier,
         AnnotatedNode,
         AstNode,
         Expression,
         SimpleIdentifier;
+import 'package:analyzer/src/generated/constant.dart' show DartObjectImpl;
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart'
     show ParseDartTask, AnalysisContext;
 import 'package:analyzer/src/generated/resolver.dart' show TypeProvider;
 import 'package:analyzer/src/generated/source.dart' show Source;
 import 'package:analyzer/analyzer.dart' show parseDirectives;
 import 'package:crypto/crypto.dart' show CryptoUtils, MD5;
 import 'package:source_span/source_span.dart';
 import 'package:yaml/yaml.dart';
 
@@ skipping 307 matching lines @@
   // It seems like we should know our package's root directory without needing
   // to search like this.
   var pubspec =
       loadYaml(new File(path.join(dir, 'pubspec.yaml')).readAsStringSync());
 
   // Ensure this is loaded from the dev_compiler package.
   if (pubspec['name'] != 'dev_compiler') return null;
   return path.join('dev_compiler', 'runtime', filename);
 }
 
+/// Given an annotated [node] and a [test] function, returns the first matching
+/// constant valued annotation.
+///
+/// For example if we had the ClassDeclaration node for `FontElement`:
+///
+///    @JsName('HTMLFontElement')
+///    @deprecated
+///    class FontElement { ... }
+///
+/// We could match `@deprecated` with a test function like:
+///
+///    (v) => v.type.name == 'Deprecated' && v.type.element.library.isDartCore
+///
+DartObjectImpl getAnnotationValue(
+    AnnotatedNode node, bool test(DartObjectImpl value)) {
+  for (var metadata in node.metadata) {
+    ElementAnnotationImpl element = metadata.elementAnnotation;
+    if (element == null) continue;
+
+    var evalResult = element.evaluationResult;
+    if (evalResult == null) continue;
+
+    var value = evalResult.value;
+    if (value != null && test(value)) return value;
+  }
+  return null;
+}
+
+/// Given a constant [value], a [fieldName], and an [expectedType], returns the
+/// value of that field.
+///
+/// If the field is missing or is not [expectedType], returns null.
+Object getConstantField(
+    DartObjectImpl value, String fieldName, DartType expectedType) {
+  if (value == null) return null;
+  var f = value.fields[fieldName];
+  return (f == null || f.type != expectedType) ? null : f.value;
+}
+
 InterfaceType fillDynamicTypeArgs(InterfaceType t, TypeProvider types) =>
     t.substitute4(new List.filled(t.typeArguments.length, types.dynamicType));