fix #569, cache constants defined in methods

lib/src/compiler/element_helpers.dart

 // Copyright (c) 2016, 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.
 
 /// Helpers for Analyzer's Element model and corelib model.
 
 import 'package:analyzer/dart/ast/ast.dart'
-    show Expression, MethodInvocation, SimpleIdentifier;
+    show
+        ConstructorDeclaration,
+        Expression,
+        FunctionBody,
+        FunctionExpression,
+        MethodDeclaration,
+        MethodInvocation,
+        SimpleIdentifier;
 import 'package:analyzer/dart/element/element.dart'
-    show Element, FunctionElement;
+    show Element, ExecutableElement, FunctionElement;
 import 'package:analyzer/dart/element/type.dart'
     show DartType, InterfaceType, ParameterizedType;
 import 'package:analyzer/src/dart/element/type.dart' show DynamicTypeImpl;
 import 'package:analyzer/src/generated/constant.dart' show DartObject;
 
 class Tuple2<T0, T1> {
   final T0 e0;
   final T1 e1;
   Tuple2(this.e0, this.e1);
 }
@@ skipping 54 matching lines @@
   var parent = node.parent;
   return parent is MethodInvocation && parent.methodName == node;
 }
 
 bool isInlineJS(Element e) =>
     e is FunctionElement &&
     e.name == 'JS' &&
     e.library.isInSdk &&
     e.library.source.uri.toString() == 'dart:_foreign_helper';
 
+ExecutableElement getFunctionBodyElement(FunctionBody body) {
+  var f = body.parent;
+  if (f is FunctionExpression) {
+    return f.element;
+  } else if (f is MethodDeclaration) {
+    return f.element;
+  } else {
+    return (f as ConstructorDeclaration).element;
+  }
+}
+
 /// Returns the value of the `name` field from the [match]ing annotation on
 /// [element], or `null` if we didn't find a valid match or it was not a string.
 ///
 /// For example, consider this code:
 ///
 ///     class MyAnnotation {
 ///       final String name;
 ///       // ...
 ///       const MyAnnotation(this.name/*, ... other params ... */);
 ///     }
 ///
 ///     @MyAnnotation('FooBar')
 ///     main() { ... }
 ///
 /// If we match the annotation for the `@MyAnnotation('FooBar')` this will
 /// return the string 'FooBar'.
 String getAnnotationName(Element element, bool match(DartObject value)) =>
     findAnnotation(element, match)?.getField('name')?.toStringValue();