A visitor that builds a map from node to "Usage".

lib/compiler/implementation/dart_backend/usage.dart

Index: lib/compiler/implementation/dart_backend/usage.dart
diff --git a/lib/compiler/implementation/dart_backend/usage.dart b/lib/compiler/implementation/dart_backend/usage.dart
new file mode 100644
index 0000000000000000000000000000000000000000..52bef9d0ce3778b0a9d7efe2d3d98584811f0051
--- /dev/null
+++ b/lib/compiler/implementation/dart_backend/usage.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2012, 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.
+
+class UsageKind {
+  final String id;
+  const UsageKind(String this.id);
+
+  static final UsageKind CONSTRUCTOR_NAME =
+      const UsageKind('constructor_name');
+  static final UsageKind TYPE =
+      const UsageKind('type');
+  static final UsageKind METHOD =
+      const UsageKind('method');
+  // Common-case resolved element. This should go away.
+  static final UsageKind ELEMENT =
+      const UsageKind('element');
+  // Do not emit.
+  static final UsageKind NULL =
+      const UsageKind('null');
+}
+
+class Usage {
+  final UsageKind kind;
+  Usage(this.kind);
+  abstract String rename(ConflictingRenamer renamer);
+}
+
+class ConstructorNameUsage extends Usage {
+  final FunctionElement constructor;
+  ConstructorNameUsage(this.constructor) : super(UsageKind.CONSTRUCTOR_NAME);
+  String rename(ConflictingRenamer renamer) =>
+      renamer.renameConstructorName(constructor);
+}
+class TypeUsage extends Usage {
+  final Type type;
+  TypeUsage(this.type) : super(UsageKind.TYPE);
+  String rename(ConflictingRenamer renamer) =>
+      renamer.renameElement(type.element);
+}
+class MethodUsage extends Usage {
+  final Element method;
+  MethodUsage(this.method) : super(UsageKind.METHOD);
+  String rename(ConflictingRenamer renamer) => renamer.renameElement(method);
+}
+class NullUsage extends Usage {
+  NullUsage() : super(UsageKind.NULL);
+  String rename(ConflictingRenamer renamer) => '';
+}
+class ElementUsage extends Usage {
+  final Element element;
+  ElementUsage(this.element) : super(UsageKind.ELEMENT);
+  String rename(ConflictingRenamer renamer) => renamer.renameElement(element);
+}