Support for extending native classes

sdk/lib/_internal/compiler/implementation/native_handler.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.
 
 library native;
 
 import 'dart:collection' show Queue;
 import 'dart2jslib.dart' hide SourceString;
 import 'dart_types.dart';
 import 'elements/elements.dart';
@@ skipping 68 matching lines @@
    * exactly one of [unusedClasses], [pendingClasses] and [registeredClasses].
    */
   final Set<ClassElement> nativeClasses = new Set<ClassElement>();
 
   final Set<ClassElement> registeredClasses = new Set<ClassElement>();
   final Set<ClassElement> pendingClasses = new Set<ClassElement>();
   final Set<ClassElement> unusedClasses = new Set<ClassElement>();
 
   bool hasInstantiatedNativeClasses() => !registeredClasses.isEmpty;
 
+  final Set<ClassElement> nativeClassesAndSubclasses = new Set<ClassElement>();
+
+  final Map<ClassElement, Set<ClassElement>> nonNativeSubclasses =
+      new Map<ClassElement, Set<ClassElement>>();
+
   /**
    * Records matched constraints ([SpecialType] or [DartType]).  Once a type
    * constraint has been matched, there is no need to match it again.
    */
   final Set matchedTypeConstraints = new Set();
 
   /// Pending actions.  Classes in [pendingClasses] have action thunks in
   /// [queue] to register the class.
   final queue = new Queue();
   bool flushing = false;
 
   /// Maps JS foreign calls to their computed native behavior.
   final Map<Node, NativeBehavior> nativeBehaviors =
       new Map<Node, NativeBehavior>();
 
   final Enqueuer world;
   final Compiler compiler;
   final bool enableLiveTypeAnalysis;
 
   ClassElement _annotationCreatesClass;
   ClassElement _annotationReturnsClass;
   ClassElement _annotationJsNameClass;
 
   /// Subclasses of [NativeEnqueuerBase] are constructed by the backend.
   NativeEnqueuerBase(this.world, this.compiler, this.enableLiveTypeAnalysis);
 
   void processNativeClasses(Iterable<LibraryElement> libraries) {
     libraries.forEach(processNativeClassesInLibrary);
     processNativeClassesInLibrary(compiler.isolateHelperLibrary);
+
+    processSubclassesOfNativeClasses(libraries);
+
     if (!enableLiveTypeAnalysis) {
       nativeClasses.forEach((c) => enqueueClass(c, 'forced'));
       flushQueue();
     }
   }
 
   void processNativeClassesInLibrary(LibraryElement library) {
     // Use implementation to ensure the inclusion of injected members.
     library.implementation.forEachLocalMember((Element element) {
       if (element.isClass() && element.isNative()) {
         processNativeClass(element);
       }
     });
   }
 
   void processNativeClass(ClassElement classElement) {
     nativeClasses.add(classElement);
     unusedClasses.add(classElement);
     // Resolve class to ensure the class has valid inheritance info.
     classElement.ensureResolved(compiler);
   }
 
+  void processSubclassesOfNativeClasses(Iterable<LibraryElement> libraries) {
+    //  class B extends foo.A {}

[ahe, 2013/08/13 18:31:47]

This comment is weird.

[sra1, 2013/08/14 04:36:47]

Done.

+
+    var potentialExtends = new Map<SourceString, Set<ClassElement>>();
+
+    libraries.forEach((library) {
+      library.implementation.forEachLocalMember((element) {
+        if (element.isClass()) {
+          SourceString name = element.name;
+          SourceString extendsName = findExtendsNameOfClass(element);
+          if (extendsName != null) {
+            Set<ClassElement> potentialSubclasses =
+                potentialExtends.putIfAbsent(
+                    extendsName,
+                    () => new Set<ClassElement>());
+            potentialSubclasses.add(element);
+          }
+        }
+      });
+    });
+
+    ClassElement nativeSuperclassOf(ClassElement classElement) {
+      if (classElement.isNative()) return classElement;
+      if (classElement.superclass == null) return null;
+      return nativeSuperclassOf(classElement.superclass);

[ahe, 2013/08/13 18:31:47]

How does this cope with cycles in the inheritance graph?

[sra1, 2013/08/14 04:36:47]

Called after resolving.

[ahe, 2013/08/14 10:52:47]

Sorry, I forgot we had solved this problem.

+    }
+
+    void walkPotentialSubclasses(ClassElement element) {
+      if (nativeClassesAndSubclasses.contains(element)) return;
+      //print('Force resolve $element');

[ahe, 2013/08/13 18:31:47]

Remove comment.

[sra1, 2013/08/14 04:36:47]

Done.

+      element.ensureResolved(compiler);
+      ClassElement nativeSuperclass = nativeSuperclassOf(element);
+      if (nativeSuperclass != null) {
+        nativeClassesAndSubclasses.add(element);
+        if (!element.isNative()) {
+          nonNativeSubclasses.putIfAbsent(nativeSuperclass,
+              () => new Set<ClassElement>())
+            .add(element);
+        }
+        Set<ClassElement> potentialSubclasses = potentialExtends[element.name];
+        if (potentialSubclasses != null) {
+          potentialSubclasses.forEach(walkPotentialSubclasses);
+        }
+      }
+    }
+
+    nativeClasses.forEach(walkPotentialSubclasses);
+
+    // print(nativeClassesAndSubclasses);
+
+    nativeClasses.addAll(nativeClassesAndSubclasses);
+    unusedClasses.addAll(nativeClassesAndSubclasses);
+
+    // NEXT: make subclassed classes use different register function; add in a

[ahe, 2013/08/13 18:31:47]

We normally use // TODO(username): ...

[sra1, 2013/08/14 04:36:47]

Removed, since it is done.

+    // hook that the DOM runtime can use.
+  }
+
+  /**
+   * Returns the source string of the class named in the extends clause, or
+   * `null` if there is no extends clause.
+   */
+  SourceString findExtendsNameOfClass(ClassElement classElement) {

[ahe, 2013/08/13 18:31:47]

I'm concerned about this method, and I would really appreciate if you would
commit to using the parser to obtain an AST node soonish.

I understand you're under pressure, but code like this has a tendency to cause a
problems real soon. So please consider it a rather high priority to clean this
up :-)

FWIW, it should be relatively easy to use PartialParser to extract this
information.

+    //  "class B extends A ... {}"  --> "A"
+    //  "class B extends foo.A ... {}"  --> "A"
+    //  "class B<T> extends foo.A<T,T> with M1, M2 ... {}"  --> "A"
+
+    // We want to avoid calling classElement.parseNode on every class.  Doing so
+    // will slightly increase parse time and size and cause compiler errors and
+    // warnings to me emitted in more unused code.
+
+    // An alternative to this code is to extend the API of ClassElement to
+    // expose the name of the extended element.
+
+    // Pattern match the above cases in the token stream.
+    //  [abstract] class X extends [id.]* id
+
+    Token skipTypeParameters(Token token) {

[ahe, 2013/08/13 18:31:47]

This should be:

    BeginGroupToken beginGroupToken = token;
    Token endToken = beginGroupToken.endGroup;
    return endToken.next;

+      for (;;) {
+        token = token.next;
+        if (token.stringValue == '>') return token.next;
+        if (token.stringValue == '<') return skipTypeParameters(token);
+      }
+    }
+
+    SourceString scanForExtendsName(Token token) {
+      if (token.stringValue == 'abstract') token = token.next;

[ahe, 2013/08/13 18:31:47]

You need to use identical, not ==. Otherwise, you do slow string comparison.

[sra1, 2013/08/14 04:36:47]

What guarantees they are the same instance of String?

[ahe, 2013/08/14 10:52:47]

That is guaranteed by the language specification (compile-time constants are
canonicalized) and the string literals passed to the Keyword constructor.

+      if (token.stringValue != 'class') return null;

[ahe, 2013/08/13 18:31:47]

Ditto.

+      token = token.next;
+      if (!token.isIdentifier()) return null;
+      token = token.next;
+      //  class F<X extends B<X>> extends ...
+      if (token.stringValue == '<') {

[ahe, 2013/08/13 18:31:47]

Ditto.

+        token = skipTypeParameters(token);
+      }
+      if (token.stringValue != 'extends') return null;

[ahe, 2013/08/13 18:31:47]

Ditto.

+      token = token.next;
+      Token id = token;
+      for (;;) {

[ahe, 2013/08/13 18:31:47]

As a general rule, infinite loops on user data is a recipe for hanging
compilers. Especially in dart2js where EOF.next is EOF.

This is why all 'infinite' loops in the parser look like this:

    while (!identical(token.kind, EOF_TOKEN)) {

In this case, identical is overkill for legacy reasons.

[sra1, 2013/08/14 04:36:47]

Done.

+        token = token.next;
+        if (token.stringValue != '.') break;

[ahe, 2013/08/13 18:31:47]

identical.

+        token = token.next;
+        if (!token.isIdentifier()) return null;
+        id = token;
+      }
+      // Should be at '{', 'with', 'implements', '<' or 'native'.
+      return id.value;
+    }
+
+    return compiler.withCurrentElement(classElement, () {
+      return scanForExtendsName(classElement.position());
+    });
+  }
+
   ClassElement get annotationCreatesClass {
     findAnnotationClasses();
     return _annotationCreatesClass;
   }
 
   ClassElement get annotationReturnsClass {
     findAnnotationClasses();
     return _annotationReturnsClass;
   }
 
@@ skipping 228 matching lines @@
     staticUse(name) => world.registerStaticUse(compiler.findHelper(name));
 
     staticUse(const SourceString('dynamicFunction'));
     staticUse(const SourceString('dynamicSetMetadata'));
     staticUse(const SourceString('defineProperty'));
     staticUse(const SourceString('toStringForNativeObject'));
     staticUse(const SourceString('hashCodeForNativeObject'));
     staticUse(const SourceString('convertDartClosureToJS'));
     staticUse(const SourceString('defineNativeMethods'));
     staticUse(const SourceString('defineNativeMethodsNonleaf'));
+    staticUse(const SourceString('defineNativeMethodsExtended'));
     // TODO(9577): Registering `defineNativeMethodsFinish` seems redundant with
     // respect to the registering in the backend. When the backend registering
     // is removed as part of fixing Issue 9577, this can be the sole place
     // registering this methods.
     staticUse(const SourceString('defineNativeMethodsFinish'));
 
     addNativeExceptions();
   }
 
   addNativeExceptions() {
@@ skipping 618 matching lines @@
           'native "..." syntax is restricted to functions with zero parameters',
           node: nativeBody);
     }
     LiteralString jsCode = nativeBody.asLiteralString();
     builder.push(new HForeign.statement(
         new js.LiteralStatement(jsCode.dartString.slowToString()),
         <HInstruction>[],
         new SideEffects()));
   }
 }