sdk/lib/_internal/compiler/implementation/js_backend/native_emitter.dart - sdk.git - Git at Google

 // 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 NativeEmitter {

   CodeEmitterTask emitter;
   CodeBuffer nativeBuffer;

   // Classes that participate in dynamic dispatch. These are the
   // classes that contain used members.
   Set<ClassElement> classesWithDynamicDispatch;

   // Native classes found in the application.
   Set<ClassElement> nativeClasses;

   // Caches the native subtypes of a native class.
   Map<ClassElement, List<ClassElement>> subtypes;

   // Caches the direct native subtypes of a native class.
   Map<ClassElement, List<ClassElement>> directSubtypes;

   // Caches the native methods that are overridden by a native class.
   // Note that the method that overrides does not have to be native:
   // it's the overridden method that must make sure it will dispatch
   // to its subclass if it sees an instance whose class is a subclass.
   Set<FunctionElement> overriddenMethods;

   // Caches the methods that have a native body.
   Set<FunctionElement> nativeMethods;

   // Do we need the native emitter to take care of handling
   // noSuchMethod for us? This flag is set to true in the emitter if
   // it finds any native class that needs noSuchMethod handling.
   bool handleNoSuchMethod = false;

   NativeEmitter(this.emitter)
       : classesWithDynamicDispatch = new Set<ClassElement>(),
         nativeClasses = new Set<ClassElement>(),
         subtypes = new Map<ClassElement, List<ClassElement>>(),
         directSubtypes = new Map<ClassElement, List<ClassElement>>(),
         overriddenMethods = new Set<FunctionElement>(),
         nativeMethods = new Set<FunctionElement>(),
         nativeBuffer = new CodeBuffer();

   Compiler get compiler => emitter.compiler;
   JavaScriptBackend get backend => compiler.backend;

   String get _ => emitter._;
   String get n => emitter.n;
   String get N => emitter.N;

   String get dynamicName {
     Element element = compiler.findHelper(
         const SourceString('dynamicFunction'));
     return backend.namer.isolateAccess(element);
   }

   String get dynamicSetMetadataName {
     Element element = compiler.findHelper(
         const SourceString('dynamicSetMetadata'));
     return backend.namer.isolateAccess(element);
   }

   String get typeNameOfName {
     Element element = compiler.findHelper(
         const SourceString('getTypeNameOf'));
     return backend.namer.isolateAccess(element);
   }

   String get defPropName {
     Element element = compiler.findHelper(
         const SourceString('defineProperty'));
     return backend.namer.isolateAccess(element);
   }

   String get toStringHelperName {
     Element element = compiler.findHelper(
         const SourceString('toStringForNativeObject'));
     return backend.namer.isolateAccess(element);
   }

   String get hashCodeHelperName {
     Element element = compiler.findHelper(
         const SourceString('hashCodeForNativeObject'));
     return backend.namer.isolateAccess(element);
   }

   String get defineNativeClassName
       => '${backend.namer.CURRENT_ISOLATE}.\$defineNativeClass';

   String get defineNativeClassFunction {
     return """
 function(cls, desc) {
   var fields = desc[''];
   var fields_array = fields ? fields.split(',') : [];
   for (var i = 0; i < fields_array.length; i++) {
     ${emitter.currentGenerateAccessorName}(fields_array[i], desc);
   }
   var hasOwnProperty = Object.prototype.hasOwnProperty;
   for (var method in desc) {
     if (method) {
       if (hasOwnProperty.call(desc, method)) {
         $dynamicName(method)[cls] = desc[method];
       }
     }
   }
 }""";
   }

   bool isNativeGlobal(String quotedName) {
     return identical(quotedName[1], '@');
   }

   String toNativeTag(ClassElement cls) {
     String quotedName = cls.nativeTagInfo.slowToString();
     if (isNativeGlobal(quotedName)) {
       // Global object, just be like the other types for now.
       return quotedName.substring(3, quotedName.length - 1);
     } else {
       return quotedName.substring(2, quotedName.length - 1);
     }
   }

   void generateNativeClass(ClassElement classElement) {
     assert(!classElement.hasBackendMembers);
     nativeClasses.add(classElement);

     ClassBuilder builder = new ClassBuilder();
     emitter.emitClassFields(classElement, builder, classIsNative: true);
     emitter.emitClassGettersSetters(classElement, builder);
     emitter.emitInstanceMembers(classElement, builder);

     // An empty native class may be omitted since the superclass methods can be
     // located via the dispatch metadata.
     if (builder.properties.isEmpty) return;

     String nativeTag = toNativeTag(classElement);
     jsAst.Expression definition =
         js[defineNativeClassName](
             [js.string(nativeTag), builder.toObjectInitializer()]);

     nativeBuffer.add(jsAst.prettyPrint(definition, compiler));
     nativeBuffer.add('$N$n');

     classesWithDynamicDispatch.add(classElement);
   }

   List<ClassElement> getDirectSubclasses(ClassElement cls) {
     List<ClassElement> result = directSubtypes[cls];
     return result == null ? const<ClassElement>[] : result;
   }

   void potentiallyConvertDartClosuresToJs(
       List<jsAst.Statement> statements,
       FunctionElement member,
       List<jsAst.Parameter> stubParameters) {
     FunctionSignature parameters = member.computeSignature(compiler);
     Element converter =
         compiler.findHelper(const SourceString('convertDartClosureToJS'));
     String closureConverter = backend.namer.isolateAccess(converter);
     Set<String> stubParameterNames = new Set<String>.from(
         stubParameters.map((param) => param.name));
     parameters.forEachParameter((Element parameter) {
       String name = parameter.name.slowToString();
       // If [name] is not in [stubParameters], then the parameter is an optional
       // parameter that was not provided for this stub.
       for (jsAst.Parameter stubParameter in stubParameters) {
         if (stubParameter.name == name) {
           DartType type = parameter.computeType(compiler).unalias(compiler);
           if (type is FunctionType) {
             // The parameter type is a function type either directly or through
             // typedef(s).
             int arity = type.computeArity();

             statements.add(
                 new jsAst.ExpressionStatement(
                     js.assign(
                         js[name],
                         js[closureConverter](
                             [js[name],
                              new jsAst.LiteralNumber('$arity')]))));
             break;
           }
         }
       }
     });
   }

   List<jsAst.Statement> generateParameterStubStatements(
       Element member,
       String invocationName,
       List<jsAst.Parameter> stubParameters,
       List<jsAst.Expression> argumentsBuffer,
       int indexOfLastOptionalArgumentInParameters) {
     // The target JS function may check arguments.length so we need to
     // make sure not to pass any unspecified optional arguments to it.
     // For example, for the following Dart method:
     //   foo([x, y, z]);
     // The call:
     //   foo(y: 1)
     // must be turned into a JS call to:
     //   foo(null, y).

     ClassElement classElement = member.enclosingElement;
     String nativeTagInfo = classElement.nativeTagInfo.slowToString();

     List<jsAst.Statement> statements = <jsAst.Statement>[];
     potentiallyConvertDartClosuresToJs(statements, member, stubParameters);

     String target;
     List<jsAst.Expression> arguments;

     if (!nativeMethods.contains(member)) {
       // When calling a method that has a native body, we call it with our
       // calling conventions.
       target = backend.namer.getName(member);
       arguments = argumentsBuffer;
     } else {
       // When calling a JS method, we call it with the native name, and only the
       // arguments up until the last one provided.
       target = member.fixedBackendName();
       arguments = argumentsBuffer.getRange(
           0, indexOfLastOptionalArgumentInParameters + 1);
     }
     statements.add(
         new jsAst.Return(
             new jsAst.VariableUse('this')[target](arguments)));

     if (!overriddenMethods.contains(member)) {
       // Call the method directly.
       return statements;
     } else {
       return <jsAst.Statement>[
           generateMethodBodyWithPrototypeCheck(
               invocationName, new jsAst.Block(statements), stubParameters)];
     }
   }

   // If a method is overridden, we must check if the prototype of 'this' has the
   // method available. Otherwise, we may end up calling the method from the
   // super class. If the method is not available, we make a direct call to
   // Object.prototype.$methodName.  This method will patch the prototype of
   // 'this' to the real method.
   jsAst.Statement generateMethodBodyWithPrototypeCheck(
       String methodName,
       jsAst.Statement body,
       List<jsAst.Parameter> parameters) {
     return js.if_(
         js['(Object.getPrototypeOf(this)).hasOwnProperty("$methodName")'],
         body,
         js.return_(
             js['Object.prototype.$methodName.call'](
                 <jsAst.Expression>[js['this']]..addAll(
                     parameters.map((param) => js[param.name])))));
   }

   jsAst.Block generateMethodBodyWithPrototypeCheckForElement(
       FunctionElement element,
       jsAst.Block body,
       List<jsAst.Parameter> parameters) {
     ElementKind kind = element.kind;
     if (kind != ElementKind.FUNCTION &&
         kind != ElementKind.GETTER &&
         kind != ElementKind.SETTER) {
       compiler.internalError("unexpected kind: '$kind'", element: element);
     }

     String methodName = backend.namer.getName(element);
     return new jsAst.Block(
         [generateMethodBodyWithPrototypeCheck(methodName, body, parameters)]);
   }


   void emitDynamicDispatchMetadata() {
     if (classesWithDynamicDispatch.isEmpty) return;
     int length = classesWithDynamicDispatch.length;
     if (!compiler.enableMinification) {
       nativeBuffer.add('// $length dynamic classes.\n');
     }

     // Build a pre-order traversal over all the classes and their subclasses.
     Set<ClassElement> seen = new Set<ClassElement>();
     List<ClassElement> classes = <ClassElement>[];
     void visit(ClassElement cls) {
       if (seen.contains(cls)) return;
       seen.add(cls);
       getDirectSubclasses(cls).forEach(visit);
       classes.add(cls);
     }
     classesWithDynamicDispatch.forEach(visit);

     List<ClassElement> preorderDispatchClasses = classes.where(
         (cls) => !getDirectSubclasses(cls).isEmpty &&
                   classesWithDynamicDispatch.contains(cls)).toList();

     if (!compiler.enableMinification) {
       nativeBuffer.add('// ${classes.length} classes\n');
     }
     Iterable<ClassElement> classesThatHaveSubclasses = classes.where(
         (ClassElement t) => !getDirectSubclasses(t).isEmpty);
     if (!compiler.enableMinification) {
       nativeBuffer.add('// ${classesThatHaveSubclasses.length} !leaf\n');
     }

     // Generate code that builds the map from cls tags used in dynamic dispatch
     // to the set of cls tags of classes that extend (TODO: or implement) those
     // classes.  The set is represented as a string of tags joined with '|'.
     // This is easily split into an array of tags, or converted into a regexp.
     //
     // To reduce the size of the sets, subsets are CSE-ed out into variables.
     // The sets could be much smaller if we could make assumptions about the
     // cls tags of other classes (which are constructor names or part of the
     // result of Object.protocls.toString).  For example, if objects that are
     // Dart objects could be easily excluded, then we might be able to simplify
     // the test, replacing dozens of HTMLxxxElement classes with the regexp
     // /HTML.*Element/.

     // Temporary variables for common substrings.
     List<String> varNames = <String>[];
     // Values of temporary variables.
     Map<String, jsAst.Expression> varDefns = new Map<String, jsAst.Expression>();

     // Expression to compute tags string for a class.  The expression will
     // initially be a string or expression building a string, but may be
     // replaced with a variable reference to the common substring.
     Map<ClassElement, jsAst.Expression> tagDefns =
         new Map<ClassElement, jsAst.Expression>();

     jsAst.Expression makeExpression(ClassElement classElement) {
       // Expression fragments for this set of cls keys.
       List<jsAst.Expression> expressions = <jsAst.Expression>[];
       // TODO: Remove if cls is abstract.
       List<String> subtags = [toNativeTag(classElement)];
       void walk(ClassElement cls) {
         for (final ClassElement subclass in getDirectSubclasses(cls)) {
           ClassElement tag = subclass;
           jsAst.Expression existing = tagDefns[tag];
           if (existing == null) {
             // [subclass] is still within the subtree between dispatch classes.
             subtags.add(toNativeTag(tag));
             walk(subclass);
           } else {
             // [subclass] is one of the preorderDispatchClasses, so CSE this
             // reference with the previous reference.
             jsAst.VariableUse use = existing.asVariableUse();
             if (use != null && varDefns.containsKey(use.name)) {
               // We end up here if the subclasses have a DAG structure.  We
               // don't have DAGs yet, but if the dispatch is used for mixins
               // that will be a possibility.
               // Re-use the previously created temporary variable.
               expressions.add(new jsAst.VariableUse(use.name));
             } else {
               String varName = 'v${varNames.length}_${tag.name.slowToString()}';
               varNames.add(varName);
               varDefns[varName] = existing;
               tagDefns[tag] = new jsAst.VariableUse(varName);
               expressions.add(new jsAst.VariableUse(varName));
             }
           }
         }
       }
       walk(classElement);

       if (!subtags.isEmpty) {
         expressions.add(js.string(subtags.join('|')));
       }
       jsAst.Expression expression;
       if (expressions.length == 1) {
         expression = expressions[0];
       } else {
         jsAst.Expression array = new jsAst.ArrayInitializer.from(expressions);
         expression = array['join']([js.string('|')]);
       }
       return expression;
     }

     for (final ClassElement classElement in preorderDispatchClasses) {
       tagDefns[classElement] = makeExpression(classElement);
     }

     // Write out a thunk that builds the metadata.
     if (!tagDefns.isEmpty) {
       List<jsAst.Statement> statements = <jsAst.Statement>[];

       List<jsAst.VariableInitialization> initializations =
           <jsAst.VariableInitialization>[];
       for (final String varName in varNames) {
         initializations.add(
             new jsAst.VariableInitialization(
                 new jsAst.VariableDeclaration(varName),
                 varDefns[varName]));
       }
       if (!initializations.isEmpty) {
         statements.add(
             new jsAst.ExpressionStatement(
                 new jsAst.VariableDeclarationList(initializations)));
       }

       // [table] is a list of lists, each inner list of the form:
       //   [dynamic-dispatch-tag, tags-of-classes-implementing-dispatch-tag]
       // E.g.
       //   [['Node', 'Text|HTMLElement|HTMLDivElement|...'], ...]
       jsAst.Expression table =
           new jsAst.ArrayInitializer.from(
               preorderDispatchClasses.map((cls) =>
                   new jsAst.ArrayInitializer.from([
                       js.string(toNativeTag(cls)),
                       tagDefns[cls]])));

       //  $.dynamicSetMetadata(table);
       statements.add(
           new jsAst.ExpressionStatement(
               new jsAst.Call(
                   new jsAst.VariableUse(dynamicSetMetadataName),
                   [table])));

       //  (function(){statements})();
       if (emitter.compiler.enableMinification) nativeBuffer.add(';');
       nativeBuffer.add(
           jsAst.prettyPrint(
               new jsAst.ExpressionStatement(
                   new jsAst.Call(new jsAst.Fun([], new jsAst.Block(statements)),
                                  [])),
               compiler));
     }
   }

   bool isSupertypeOfNativeClass(Element element) {
     if (element.isTypeVariable()) {
       compiler.cancel("Is check for type variable", element: element);
       return false;
     }
     if (element.computeType(compiler).unalias(compiler) is FunctionType) {
       // The element type is a function type either directly or through
       // typedef(s).
       return false;
     }

     if (!element.isClass()) {
       compiler.cancel("Is check does not handle element", element: element);
       return false;
     }

     return subtypes[element] != null;
   }

   bool requiresNativeIsCheck(Element element) {
     if (!element.isClass()) return false;
     ClassElement cls = element;
     if (cls.isNative()) return true;
     return isSupertypeOfNativeClass(element);
   }

   void assembleCode(CodeBuffer targetBuffer) {
     if (nativeClasses.isEmpty) return;
     emitDynamicDispatchMetadata();
     targetBuffer.add('$defineNativeClassName = '
                      '$defineNativeClassFunction$N$n');

     List<jsAst.Property> objectProperties = <jsAst.Property>[];

     void addProperty(String name, jsAst.Expression value) {
       objectProperties.add(new jsAst.Property(js.string(name), value));
     }

     // Because of native classes, we have to generate some is checks
     // by calling a method, instead of accessing a property. So we
     // attach to the JS Object prototype these methods that return
     // false, and will be overridden by subclasses when they have to
     // return true.
     void emitIsChecks() {
       for (ClassElement element in
                Elements.sortedByPosition(emitter.checkedClasses)) {
         if (!requiresNativeIsCheck(element)) continue;
         if (element.isObject(compiler)) continue;
         String name = backend.namer.operatorIs(element);
         addProperty(name,
             js.fun([], js.return_(js['false'])));
       }
     }
     emitIsChecks();

     jsAst.Expression makeCallOnThis(String functionName) {
       return js.fun([], js.return_(js['$functionName(this)']));
     }

     // In order to have the toString method on every native class,
     // we must patch the JS Object prototype with a helper method.
     String toStringName = backend.namer.publicInstanceMethodNameByArity(
         const SourceString('toString'), 0);
     addProperty(toStringName, makeCallOnThis(toStringHelperName));

     // Same as above, but for hashCode.
     String hashCodeName =
         backend.namer.publicGetterName(const SourceString('hashCode'));
     addProperty(hashCodeName, makeCallOnThis(hashCodeHelperName));

     // Same as above, but for operator==.
     String equalsName = backend.namer.publicInstanceMethodNameByArity(
         const SourceString('=='), 1);
     addProperty(equalsName, js.fun(['a'],
         js.return_(js['this === a'])));

     // If the native emitter has been asked to take care of the
     // noSuchMethod handlers, we do that now.
     if (handleNoSuchMethod) {
       emitter.emitNoSuchMethodHandlers(addProperty);
     }

     // If we have any properties to add to Object.prototype, we run
     // through them and add them using defineProperty.
     if (!objectProperties.isEmpty) {
       jsAst.Expression init =
           js.fun(['table'],
               new jsAst.ForIn(
                   new jsAst.VariableDeclarationList(
                       [new jsAst.VariableInitialization(
                           new jsAst.VariableDeclaration('key'),
                           null)]),
                   js['table'],
                   new jsAst.ExpressionStatement(
                       js['$defPropName(Object.prototype, key, table[key])'])))(
               new jsAst.ObjectInitializer(objectProperties));

       if (emitter.compiler.enableMinification) targetBuffer.add(';');
       targetBuffer.add(jsAst.prettyPrint(
           new jsAst.ExpressionStatement(init), compiler));
       targetBuffer.add('\n');
     }

     targetBuffer.add(nativeBuffer);
     targetBuffer.add('\n');
   }
 }
	// 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 NativeEmitter {

	CodeEmitterTask emitter;
	CodeBuffer nativeBuffer;

	// Classes that participate in dynamic dispatch. These are the
	// classes that contain used members.
	Set<ClassElement> classesWithDynamicDispatch;

	// Native classes found in the application.
	Set<ClassElement> nativeClasses;

	// Caches the native subtypes of a native class.
	Map<ClassElement, List<ClassElement>> subtypes;

	// Caches the direct native subtypes of a native class.
	Map<ClassElement, List<ClassElement>> directSubtypes;

	// Caches the native methods that are overridden by a native class.
	// Note that the method that overrides does not have to be native:
	// it's the overridden method that must make sure it will dispatch
	// to its subclass if it sees an instance whose class is a subclass.
	Set<FunctionElement> overriddenMethods;

	// Caches the methods that have a native body.
	Set<FunctionElement> nativeMethods;

	// Do we need the native emitter to take care of handling
	// noSuchMethod for us? This flag is set to true in the emitter if
	// it finds any native class that needs noSuchMethod handling.
	bool handleNoSuchMethod = false;

	NativeEmitter(this.emitter)
	: classesWithDynamicDispatch = new Set<ClassElement>(),
	nativeClasses = new Set<ClassElement>(),
	subtypes = new Map<ClassElement, List<ClassElement>>(),
	directSubtypes = new Map<ClassElement, List<ClassElement>>(),
	overriddenMethods = new Set<FunctionElement>(),
	nativeMethods = new Set<FunctionElement>(),
	nativeBuffer = new CodeBuffer();

	Compiler get compiler => emitter.compiler;
	JavaScriptBackend get backend => compiler.backend;

	String get _ => emitter._;
	String get n => emitter.n;
	String get N => emitter.N;

	String get dynamicName {
	Element element = compiler.findHelper(
	const SourceString('dynamicFunction'));
	return backend.namer.isolateAccess(element);
	}

	String get dynamicSetMetadataName {
	Element element = compiler.findHelper(
	const SourceString('dynamicSetMetadata'));
	return backend.namer.isolateAccess(element);
	}

	String get typeNameOfName {
	Element element = compiler.findHelper(
	const SourceString('getTypeNameOf'));
	return backend.namer.isolateAccess(element);
	}

	String get defPropName {
	Element element = compiler.findHelper(
	const SourceString('defineProperty'));
	return backend.namer.isolateAccess(element);
	}

	String get toStringHelperName {
	Element element = compiler.findHelper(
	const SourceString('toStringForNativeObject'));
	return backend.namer.isolateAccess(element);
	}

	String get hashCodeHelperName {
	Element element = compiler.findHelper(
	const SourceString('hashCodeForNativeObject'));
	return backend.namer.isolateAccess(element);
	}

	String get defineNativeClassName
	=> '${backend.namer.CURRENT_ISOLATE}.\$defineNativeClass';

	String get defineNativeClassFunction {
	return """
	function(cls, desc) {
	var fields = desc[''];
	var fields_array = fields ? fields.split(',') : [];
	for (var i = 0; i < fields_array.length; i++) {
	${emitter.currentGenerateAccessorName}(fields_array[i], desc);
	}
	var hasOwnProperty = Object.prototype.hasOwnProperty;
	for (var method in desc) {
	if (method) {
	if (hasOwnProperty.call(desc, method)) {
	$dynamicName(method)[cls] = desc[method];
	}
	}
	}
	}""";
	}

	bool isNativeGlobal(String quotedName) {
	return identical(quotedName[1], '@');
	}

	String toNativeTag(ClassElement cls) {
	String quotedName = cls.nativeTagInfo.slowToString();
	if (isNativeGlobal(quotedName)) {
	// Global object, just be like the other types for now.
	return quotedName.substring(3, quotedName.length - 1);
	} else {
	return quotedName.substring(2, quotedName.length - 1);
	}
	}

	void generateNativeClass(ClassElement classElement) {
	assert(!classElement.hasBackendMembers);
	nativeClasses.add(classElement);

	ClassBuilder builder = new ClassBuilder();
	emitter.emitClassFields(classElement, builder, classIsNative: true);
	emitter.emitClassGettersSetters(classElement, builder);
	emitter.emitInstanceMembers(classElement, builder);

	// An empty native class may be omitted since the superclass methods can be
	// located via the dispatch metadata.
	if (builder.properties.isEmpty) return;

	String nativeTag = toNativeTag(classElement);
	jsAst.Expression definition =
	js[defineNativeClassName](
	[js.string(nativeTag), builder.toObjectInitializer()]);

	nativeBuffer.add(jsAst.prettyPrint(definition, compiler));
	nativeBuffer.add('$N$n');

	classesWithDynamicDispatch.add(classElement);
	}

	List<ClassElement> getDirectSubclasses(ClassElement cls) {
	List<ClassElement> result = directSubtypes[cls];
	return result == null ? const<ClassElement>[] : result;
	}

	void potentiallyConvertDartClosuresToJs(
	List<jsAst.Statement> statements,
	FunctionElement member,
	List<jsAst.Parameter> stubParameters) {
	FunctionSignature parameters = member.computeSignature(compiler);
	Element converter =
	compiler.findHelper(const SourceString('convertDartClosureToJS'));
	String closureConverter = backend.namer.isolateAccess(converter);
	Set<String> stubParameterNames = new Set<String>.from(
	stubParameters.map((param) => param.name));
	parameters.forEachParameter((Element parameter) {
	String name = parameter.name.slowToString();
	// If [name] is not in [stubParameters], then the parameter is an optional
	// parameter that was not provided for this stub.
	for (jsAst.Parameter stubParameter in stubParameters) {
	if (stubParameter.name == name) {
	DartType type = parameter.computeType(compiler).unalias(compiler);
	if (type is FunctionType) {
	// The parameter type is a function type either directly or through
	// typedef(s).
	int arity = type.computeArity();

	statements.add(
	new jsAst.ExpressionStatement(
	js.assign(
	js[name],
	js[closureConverter](
	[js[name],
	new jsAst.LiteralNumber('$arity')]))));
	break;
	}
	}
	}
	});
	}

	List<jsAst.Statement> generateParameterStubStatements(
	Element member,
	String invocationName,
	List<jsAst.Parameter> stubParameters,
	List<jsAst.Expression> argumentsBuffer,
	int indexOfLastOptionalArgumentInParameters) {
	// The target JS function may check arguments.length so we need to
	// make sure not to pass any unspecified optional arguments to it.
	// For example, for the following Dart method:
	// foo([x, y, z]);
	// The call:
	// foo(y: 1)
	// must be turned into a JS call to:
	// foo(null, y).

	ClassElement classElement = member.enclosingElement;
	String nativeTagInfo = classElement.nativeTagInfo.slowToString();

	List<jsAst.Statement> statements = <jsAst.Statement>[];
	potentiallyConvertDartClosuresToJs(statements, member, stubParameters);

	String target;
	List<jsAst.Expression> arguments;

	if (!nativeMethods.contains(member)) {
	// When calling a method that has a native body, we call it with our
	// calling conventions.
	target = backend.namer.getName(member);
	arguments = argumentsBuffer;
	} else {
	// When calling a JS method, we call it with the native name, and only the
	// arguments up until the last one provided.
	target = member.fixedBackendName();
	arguments = argumentsBuffer.getRange(
	0, indexOfLastOptionalArgumentInParameters + 1);
	}
	statements.add(
	new jsAst.Return(
	new jsAst.VariableUse('this')[target](arguments)));

	if (!overriddenMethods.contains(member)) {
	// Call the method directly.
	return statements;
	} else {
	return <jsAst.Statement>[
	generateMethodBodyWithPrototypeCheck(
	invocationName, new jsAst.Block(statements), stubParameters)];
	}
	}

	// If a method is overridden, we must check if the prototype of 'this' has the
	// method available. Otherwise, we may end up calling the method from the
	// super class. If the method is not available, we make a direct call to
	// Object.prototype.$methodName. This method will patch the prototype of
	// 'this' to the real method.
	jsAst.Statement generateMethodBodyWithPrototypeCheck(
	String methodName,
	jsAst.Statement body,
	List<jsAst.Parameter> parameters) {
	return js.if_(
	js['(Object.getPrototypeOf(this)).hasOwnProperty("$methodName")'],
	body,
	js.return_(
	js['Object.prototype.$methodName.call'](
	<jsAst.Expression>[js['this']]..addAll(
	parameters.map((param) => js[param.name])))));
	}

	jsAst.Block generateMethodBodyWithPrototypeCheckForElement(
	FunctionElement element,
	jsAst.Block body,
	List<jsAst.Parameter> parameters) {
	ElementKind kind = element.kind;
	if (kind != ElementKind.FUNCTION &&
	kind != ElementKind.GETTER &&
	kind != ElementKind.SETTER) {
	compiler.internalError("unexpected kind: '$kind'", element: element);
	}

	String methodName = backend.namer.getName(element);
	return new jsAst.Block(
	[generateMethodBodyWithPrototypeCheck(methodName, body, parameters)]);
	}


	void emitDynamicDispatchMetadata() {
	if (classesWithDynamicDispatch.isEmpty) return;
	int length = classesWithDynamicDispatch.length;
	if (!compiler.enableMinification) {
	nativeBuffer.add('// $length dynamic classes.\n');
	}

	// Build a pre-order traversal over all the classes and their subclasses.
	Set<ClassElement> seen = new Set<ClassElement>();
	List<ClassElement> classes = <ClassElement>[];
	void visit(ClassElement cls) {
	if (seen.contains(cls)) return;
	seen.add(cls);
	getDirectSubclasses(cls).forEach(visit);
	classes.add(cls);
	}
	classesWithDynamicDispatch.forEach(visit);

	List<ClassElement> preorderDispatchClasses = classes.where(
	(cls) => !getDirectSubclasses(cls).isEmpty &&
	classesWithDynamicDispatch.contains(cls)).toList();

	if (!compiler.enableMinification) {
	nativeBuffer.add('// ${classes.length} classes\n');
	}
	Iterable<ClassElement> classesThatHaveSubclasses = classes.where(
	(ClassElement t) => !getDirectSubclasses(t).isEmpty);
	if (!compiler.enableMinification) {
	nativeBuffer.add('// ${classesThatHaveSubclasses.length} !leaf\n');
	}

	// Generate code that builds the map from cls tags used in dynamic dispatch
	// to the set of cls tags of classes that extend (TODO: or implement) those
	// classes. The set is represented as a string of tags joined with '\|'.
	// This is easily split into an array of tags, or converted into a regexp.
	//
	// To reduce the size of the sets, subsets are CSE-ed out into variables.
	// The sets could be much smaller if we could make assumptions about the
	// cls tags of other classes (which are constructor names or part of the
	// result of Object.protocls.toString). For example, if objects that are
	// Dart objects could be easily excluded, then we might be able to simplify
	// the test, replacing dozens of HTMLxxxElement classes with the regexp
	// /HTML.*Element/.

	// Temporary variables for common substrings.
	List<String> varNames = <String>[];
	// Values of temporary variables.
	Map<String, jsAst.Expression> varDefns = new Map<String, jsAst.Expression>();

	// Expression to compute tags string for a class. The expression will
	// initially be a string or expression building a string, but may be
	// replaced with a variable reference to the common substring.
	Map<ClassElement, jsAst.Expression> tagDefns =
	new Map<ClassElement, jsAst.Expression>();

	jsAst.Expression makeExpression(ClassElement classElement) {
	// Expression fragments for this set of cls keys.
	List<jsAst.Expression> expressions = <jsAst.Expression>[];
	// TODO: Remove if cls is abstract.
	List<String> subtags = [toNativeTag(classElement)];
	void walk(ClassElement cls) {
	for (final ClassElement subclass in getDirectSubclasses(cls)) {
	ClassElement tag = subclass;
	jsAst.Expression existing = tagDefns[tag];
	if (existing == null) {
	// [subclass] is still within the subtree between dispatch classes.
	subtags.add(toNativeTag(tag));
	walk(subclass);
	} else {
	// [subclass] is one of the preorderDispatchClasses, so CSE this
	// reference with the previous reference.
	jsAst.VariableUse use = existing.asVariableUse();
	if (use != null && varDefns.containsKey(use.name)) {
	// We end up here if the subclasses have a DAG structure. We
	// don't have DAGs yet, but if the dispatch is used for mixins
	// that will be a possibility.
	// Re-use the previously created temporary variable.
	expressions.add(new jsAst.VariableUse(use.name));
	} else {
	String varName = 'v${varNames.length}_${tag.name.slowToString()}';
	varNames.add(varName);
	varDefns[varName] = existing;
	tagDefns[tag] = new jsAst.VariableUse(varName);
	expressions.add(new jsAst.VariableUse(varName));
	}
	}
	}
	}
	walk(classElement);

	if (!subtags.isEmpty) {
	expressions.add(js.string(subtags.join('\|')));
	}
	jsAst.Expression expression;
	if (expressions.length == 1) {
	expression = expressions[0];
	} else {
	jsAst.Expression array = new jsAst.ArrayInitializer.from(expressions);
	expression = array['join']([js.string('\|')]);
	}
	return expression;
	}

	for (final ClassElement classElement in preorderDispatchClasses) {
	tagDefns[classElement] = makeExpression(classElement);
	}

	// Write out a thunk that builds the metadata.
	if (!tagDefns.isEmpty) {
	List<jsAst.Statement> statements = <jsAst.Statement>[];

	List<jsAst.VariableInitialization> initializations =
	<jsAst.VariableInitialization>[];
	for (final String varName in varNames) {
	initializations.add(
	new jsAst.VariableInitialization(
	new jsAst.VariableDeclaration(varName),
	varDefns[varName]));
	}
	if (!initializations.isEmpty) {
	statements.add(
	new jsAst.ExpressionStatement(
	new jsAst.VariableDeclarationList(initializations)));
	}

	// [table] is a list of lists, each inner list of the form:
	// [dynamic-dispatch-tag, tags-of-classes-implementing-dispatch-tag]
	// E.g.
	// [['Node', 'Text\|HTMLElement\|HTMLDivElement\|...'], ...]
	jsAst.Expression table =
	new jsAst.ArrayInitializer.from(
	preorderDispatchClasses.map((cls) =>
	new jsAst.ArrayInitializer.from([
	js.string(toNativeTag(cls)),
	tagDefns[cls]])));

	// $.dynamicSetMetadata(table);
	statements.add(
	new jsAst.ExpressionStatement(
	new jsAst.Call(
	new jsAst.VariableUse(dynamicSetMetadataName),
	[table])));

	// (function(){statements})();
	if (emitter.compiler.enableMinification) nativeBuffer.add(';');
	nativeBuffer.add(
	jsAst.prettyPrint(
	new jsAst.ExpressionStatement(
	new jsAst.Call(new jsAst.Fun([], new jsAst.Block(statements)),
	[])),
	compiler));
	}
	}

	bool isSupertypeOfNativeClass(Element element) {
	if (element.isTypeVariable()) {
	compiler.cancel("Is check for type variable", element: element);
	return false;
	}
	if (element.computeType(compiler).unalias(compiler) is FunctionType) {
	// The element type is a function type either directly or through
	// typedef(s).
	return false;
	}

	if (!element.isClass()) {
	compiler.cancel("Is check does not handle element", element: element);
	return false;
	}

	return subtypes[element] != null;
	}

	bool requiresNativeIsCheck(Element element) {
	if (!element.isClass()) return false;
	ClassElement cls = element;
	if (cls.isNative()) return true;
	return isSupertypeOfNativeClass(element);
	}

	void assembleCode(CodeBuffer targetBuffer) {
	if (nativeClasses.isEmpty) return;
	emitDynamicDispatchMetadata();
	targetBuffer.add('$defineNativeClassName = '
	'$defineNativeClassFunction$N$n');

	List<jsAst.Property> objectProperties = <jsAst.Property>[];

	void addProperty(String name, jsAst.Expression value) {
	objectProperties.add(new jsAst.Property(js.string(name), value));
	}

	// Because of native classes, we have to generate some is checks
	// by calling a method, instead of accessing a property. So we
	// attach to the JS Object prototype these methods that return
	// false, and will be overridden by subclasses when they have to
	// return true.
	void emitIsChecks() {
	for (ClassElement element in
	Elements.sortedByPosition(emitter.checkedClasses)) {
	if (!requiresNativeIsCheck(element)) continue;
	if (element.isObject(compiler)) continue;
	String name = backend.namer.operatorIs(element);
	addProperty(name,
	js.fun([], js.return_(js['false'])));
	}
	}
	emitIsChecks();

	jsAst.Expression makeCallOnThis(String functionName) {
	return js.fun([], js.return_(js['$functionName(this)']));
	}

	// In order to have the toString method on every native class,
	// we must patch the JS Object prototype with a helper method.
	String toStringName = backend.namer.publicInstanceMethodNameByArity(
	const SourceString('toString'), 0);
	addProperty(toStringName, makeCallOnThis(toStringHelperName));

	// Same as above, but for hashCode.
	String hashCodeName =
	backend.namer.publicGetterName(const SourceString('hashCode'));
	addProperty(hashCodeName, makeCallOnThis(hashCodeHelperName));

	// Same as above, but for operator==.
	String equalsName = backend.namer.publicInstanceMethodNameByArity(
	const SourceString('=='), 1);
	addProperty(equalsName, js.fun(['a'],
	js.return_(js['this === a'])));

	// If the native emitter has been asked to take care of the
	// noSuchMethod handlers, we do that now.
	if (handleNoSuchMethod) {
	emitter.emitNoSuchMethodHandlers(addProperty);
	}

	// If we have any properties to add to Object.prototype, we run
	// through them and add them using defineProperty.
	if (!objectProperties.isEmpty) {
	jsAst.Expression init =
	js.fun(['table'],
	new jsAst.ForIn(
	new jsAst.VariableDeclarationList(
	[new jsAst.VariableInitialization(
	new jsAst.VariableDeclaration('key'),
	null)]),
	js['table'],
	new jsAst.ExpressionStatement(
	js['$defPropName(Object.prototype, key, table[key])'])))(
	new jsAst.ObjectInitializer(objectProperties));

	if (emitter.compiler.enableMinification) targetBuffer.add(';');
	targetBuffer.add(jsAst.prettyPrint(
	new jsAst.ExpressionStatement(init), compiler));
	targetBuffer.add('\n');
	}

	targetBuffer.add(nativeBuffer);
	targetBuffer.add('\n');
	}
	}