Retain fewer names for reflection.

dart/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

 // 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.
 
 part of js_backend;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked;
 
   JavaScriptItemCompilationContext()
@@ skipping 290 matching lines @@
   /// example, if [mustRetainMetadata] is true but there is no metadata in the
   /// program, this variable will stil be false.
   bool hasRetainedMetadata = false;
 
   /// True if a call to preserveNames has been seen.
   bool mustPreserveNames = false;
 
   /// True if a call to disableTreeShaking has been seen.
   bool isTreeShakingDisabled = false;
 
+  /// True if there isn't sufficient @MirrorsUsed data.
+  bool hasInsufficientMirrorsUsed = false;
+
   /// List of instantiated types from metadata.  If metadata must be preserved,
   /// these types must registered.
   final List<Dependency> metadataInstantiatedTypes = <Dependency>[];
 
   /// List of elements used from metadata.  If metadata must be preserved,
   /// these elements must be compiled.
   final List<Element> metadataStaticUse = <Element>[];
 
   /// List of tear-off functions referenced from metadata.  If metadata must be
   /// preserved, these elements must be compiled.
@@ skipping 1031 matching lines @@
   ClassElement get fixedListImplementation => jsFixedArrayClass;
   ClassElement get growableListImplementation => jsExtendableArrayClass;
   ClassElement get mapImplementation => mapLiteralClass;
   ClassElement get constMapImplementation => constMapLiteralClass;
   ClassElement get typeImplementation => typeLiteralClass;
   ClassElement get boolImplementation => jsBoolClass;
   ClassElement get nullImplementation => jsNullClass;
 
   void registerStaticUse(Element element, Enqueuer enqueuer) {
     if (element == disableTreeShakingMarker) {
-      enqueuer.enqueueEverything();
-      if (isTreeShakingDisabled) return;
       compiler.disableTypeInferenceForMirrors = true;
       isTreeShakingDisabled = true;
+      enqueuer.enqueueEverything();
     } else if (element == preserveNamesMarker) {
       if (mustPreserveNames) return;
       mustPreserveNames = true;
       compiler.log('Preserving names.');
     } else if (element == preserveMetadataMarker) {
       if (mustRetainMetadata) return;
       compiler.log('Retaining metadata.');
       mustRetainMetadata = true;
       for (LibraryElement library in compiler.libraries.values) {
         if (retainMetadataOf(library)) {
@@ skipping 12 matching lines @@
       metadataStaticUse.clear();
       for (Element e in metadataGetOfStaticFunction) {
         registerMetadataGetOfStaticFunction(e);
       }
       metadataGetOfStaticFunction.clear();
     }
   }
 
   /// Called when [:const Symbol(name):] is seen.
   void registerConstSymbol(String name, TreeElements elements) {
+    symbolsUsed.add(name);
   }
 
   /// Called when [:new Symbol(...):] is seen.
   void registerNewSymbol(TreeElements elements) {
   }
 
-  bool retainGetter(Element element) => isTreeShakingDisabled;
+  /// Should [element] (a getter) be retained for reflection?
+  bool shouldRetainGetter(Element element) => isNeededForReflection(element);
 
-  bool retainSetter(Element element) => isTreeShakingDisabled;
+  /// Should [element] (a setter) be retained for reflection?
+  bool shouldRetainSetter(Element element) => isNeededForReflection(element);
 
-  bool retainName(SourceString name) => mustPreserveNames;
+  /// Should [name] be retained for reflection?
+  bool shouldRetainName(SourceString name) {
+    if (hasInsufficientMirrorsUsed) return mustPreserveNames;
+    if (name == const SourceString('')) return false;
+    return symbolsUsed.contains(name.slowToString());
+  }
 
   bool get rememberLazies => isTreeShakingDisabled;
 
   bool retainMetadataOf(Element element) {
     if (mustRetainMetadata) {
       // TODO(ahe): This is a little hacky, but I'll have to rewrite this when
       // implementing @MirrorsUsed anyways.
       compiler.constantHandler.compiledConstants.addAll(
           compiler.metadataHandler.compiledConstants);
       compiler.metadataHandler.compiledConstants.clear();
@@ skipping 34 matching lines @@
     if (mustRetainMetadata) {
       compiler.constantHandler.registerGetOfStaticFunction(element);
     } else {
       metadataGetOfStaticFunction.add(element);
     }
   }
 
   void registerMirrorUsage(Set<String> symbols,
                            Set<Element> targets,
                            Set<Element> metaTargets) {
+    if (symbols == null && targets == null && metaTargets == null) {
+      // The user didn't specify anything, or there are imports of
+      // 'dart:mirrors' without @MirrorsUsed.
+      hasInsufficientMirrorsUsed = true;
+      return;
+    }
     if (symbols != null) symbolsUsed.addAll(symbols);
     if (targets != null) {
       for (Element target in targets) {
         if (target.isAbstractField()) {
           AbstractFieldElement field = target;
           targetsUsed.add(field.getter);
           targetsUsed.add(field.setter);
         } else {
           targetsUsed.add(target);
         }
       }
     }
     if (metaTargets != null) metaTargetsUsed.addAll(metaTargets);
   }
 
   bool isNeededForReflection(Element element) {
-    // TODO(ahe): Implement this.
-    if (!metaTargetsUsed.isEmpty) return true;
+    if (hasInsufficientMirrorsUsed) return isTreeShakingDisabled;
+    /// Record the name of [element] in [symbolsUsed]. Return true for
+    /// convenience.
+    bool registerNameOf(Element element) {
+      symbolsUsed.add(element.name.slowToString());
+      if (element.isConstructor()) {
+        symbolsUsed.add(element.getEnclosingClass().name.slowToString());
+      }
+      return true;
+    }
+
+    if (!metaTargetsUsed.isEmpty) {
+      // TODO(ahe): Implement this.
+      return registerNameOf(element);
+    }
+
     if (!targetsUsed.isEmpty) {
       for (Element e = element; e != null; e = e.enclosingElement) {
-        if (targetsUsed.contains(e)) return true;
+        if (targetsUsed.contains(e)) return registerNameOf(element);
       }
     }
     return false;
   }
 }
 
 /// Records that [type] is used by [user.element].
 class Dependency {
   final DartType type;
   final TreeElements user;
 
   const Dependency(this.type, this.user);
 }