Support runtime check of function types.

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()
       : boundsChecked = new Set<HInstruction>();
 }
 
+
+class CheckedModeHelper {
+  final SourceString name;
+
+  const CheckedModeHelper(SourceString this.name);
+
+  Element getElement(Compiler compiler) => compiler.findHelper(name);
+
+  jsAst.Expression generateCall(SsaCodeGenerator codegen,
+                                HTypeConversion node) {
+    Element helperElement = getElement(codegen.compiler);
+    codegen.world.registerStaticUse(helperElement);
+    List<jsAst.Expression> arguments = <jsAst.Expression>[];
+    codegen.use(node.checkedInput);
+    arguments.add(codegen.pop());
+    generateAdditionalArguments(codegen, node, arguments);
+    String helperName = codegen.backend.namer.isolateAccess(helperElement);
+    return new jsAst.Call(new jsAst.VariableUse(helperName), arguments);
+  }
+
+  void generateAdditionalArguments(SsaCodeGenerator codegen,
+                                   HTypeConversion node,
+                                   List<jsAst.Expression> arguments) {
+    assert(!node.typeExpression.isMalformed);
+    // No additional arguments needed.
+  }
+}
+
+class PropertyCheckedModeHelper extends CheckedModeHelper {
+  const PropertyCheckedModeHelper(SourceString name) : super(name);
+
+  void generateAdditionalArguments(SsaCodeGenerator codegen,
+                                   HTypeConversion node,
+                                   List<jsAst.Expression> arguments) {
+    DartType type = node.typeExpression;
+    assert(!type.isMalformed);
+    String additionalArgument = codegen.backend.namer.operatorIsType(type);
+    arguments.add(js.string(additionalArgument));
+  }
+}
+
+class TypeVariableCheckedModeHelper extends CheckedModeHelper {
+  const TypeVariableCheckedModeHelper(SourceString name) : super(name);
+
+  void generateAdditionalArguments(SsaCodeGenerator codegen,
+                                   HTypeConversion node,
+                                   List<jsAst.Expression> arguments) {
+    assert(node.typeExpression.kind == TypeKind.TYPE_VARIABLE);
+    codegen.use(node.typeRepresentation);
+    arguments.add(codegen.pop());
+  }
+}
+
+class SubtypeCheckedModeHelper extends CheckedModeHelper {
+  const SubtypeCheckedModeHelper(SourceString name) : super(name);
+
+  void generateAdditionalArguments(SsaCodeGenerator codegen,
+                                   HTypeConversion node,
+                                   List<jsAst.Expression> arguments) {
+    DartType type = node.typeExpression;
+    Element element = type.element;
+    String isField = codegen.backend.namer.operatorIs(element);
+    arguments.add(js.string(isField));
+    codegen.use(node.typeRepresentation);
+    arguments.add(codegen.pop());
+    String asField = codegen.backend.namer.substitutionName(element);
+    arguments.add(js.string(asField));
+  }
+}
+
+class FunctionTypeCheckedModeHelper extends CheckedModeHelper {
+  const FunctionTypeCheckedModeHelper(SourceString name) : super(name);
+
+  void generateAdditionalArguments(SsaCodeGenerator codegen,
+                                   HTypeConversion node,
+                                   List<jsAst.Expression> arguments) {
+    DartType type = node.typeExpression;
+    String signatureName = codegen.backend.namer.getFunctionTypeName(type);
+    arguments.add(js.string(signatureName));
+
+    if (type.containsTypeVariables) {
+      ClassElement contextClass = Types.getClassContext(type);
+      String contextName = codegen.backend.namer.getName(contextClass);
+      arguments.add(js.string(contextName));
+
+      if (node.contextIsTypeArguments) {
+        arguments.add(new jsAst.LiteralNull());
+        codegen.use(node.context);
+        arguments.add(codegen.pop());
+      } else {
+        codegen.use(node.context);
+        arguments.add(codegen.pop());
+      }
+    }
+  }
+}
+
+class MalformedCheckedModeHelper extends CheckedModeHelper {
+  const MalformedCheckedModeHelper(SourceString name) : super(name);
+
+  void generateAdditionalArguments(SsaCodeGenerator codegen,
+                                   HTypeConversion node,
+                                   List<jsAst.Expression> arguments) {
+    DartType type = node.typeExpression;
+    assert(type.isMalformed);
+    String reasons = Types.fetchReasonsFromMalformedType(type);
+    arguments.add(js.string('$type'));
+    // TODO(johnniwinther): Handle escaping correctly.
+    arguments.add(js.string(reasons));
+  }
+}
+
+
 class JavaScriptBackend extends Backend {
   SsaBuilderTask builder;
   SsaOptimizerTask optimizer;
   SsaCodeGeneratorTask generator;
   CodeEmitterTask emitter;
 
   /**
    * The generated code as a js AST for compiled methods.
    */
   Map<Element, jsAst.Expression> get generatedCode {
@@ skipping 582 matching lines @@
   }
 
   void registerSetRuntimeType(TreeElements elements) {
     enqueueInResolution(getSetRuntimeTypeInfo(), elements);
   }
 
   void registerGetRuntimeTypeArgument(TreeElements elements) {
     enqueueInResolution(getGetRuntimeTypeArgument(), elements);
   }
 
-  void registerRuntimeType(TreeElements elements) {
+  void registerGenericCallMethod(Element callMethod,
+                                 Enqueuer enqueuer, TreeElements elements) {
+    if (enqueuer.isResolutionQueue || methodNeedsRti(callMethod)) {
+      registerComputeSignature(enqueuer, elements);
+    }
+  }
+
+  void registerGenericClosure(Element closure,
+                              Enqueuer enqueuer, TreeElements elements) {
+    if (enqueuer.isResolutionQueue || methodNeedsRti(closure)) {
+      registerComputeSignature(enqueuer, elements);
+    }
+  }
+
+  void registerComputeSignature(Enqueuer enqueuer, TreeElements elements) {
+    // Calls to [:computeSignature:] are generated by the emitter and we
+    // therefore need to enqueue the used elements in the codegen enqueuer as
+    // well as in the resolution enqueuer.
+    enqueue(enqueuer, getSetRuntimeTypeInfo(), elements);
+    enqueue(enqueuer, getGetRuntimeTypeInfo(), elements);
+    enqueue(enqueuer, getComputeSignature(), elements);
+    enqueue(enqueuer, getGetRuntimeTypeArguments(), elements);
+    enqueuer.registerInstantiatedClass(compiler.listClass, elements);
+  }
+
+  void registerRuntimeType(Enqueuer enqueuer, TreeElements elements) {
+    registerComputeSignature(enqueuer, elements);
     enqueueInResolution(getSetRuntimeTypeInfo(), elements);
     enqueueInResolution(getGetRuntimeTypeInfo(), elements);
-    enqueueInResolution(getGetRuntimeTypeArgument(), elements);
+    registerGetRuntimeTypeArgument(elements);
     compiler.enqueuer.resolution.registerInstantiatedClass(
         compiler.listClass, elements);
   }
 
   void registerTypeVariableExpression(TreeElements elements) {
-    registerRuntimeType(elements);
+    enqueueInResolution(getSetRuntimeTypeInfo(), elements);
+    enqueueInResolution(getGetRuntimeTypeInfo(), elements);
+    registerGetRuntimeTypeArgument(elements);
+    compiler.enqueuer.resolution.registerInstantiatedClass(
+        compiler.listClass, elements);
     enqueueInResolution(getRuntimeTypeToString(), elements);
     enqueueInResolution(getCreateRuntimeType(), elements);
   }
 
   void registerIsCheck(DartType type, Enqueuer world, TreeElements elements) {
+    type = type.unalias(compiler);
     world.registerInstantiatedClass(compiler.boolClass, elements);
+    bool inCheckedMode = compiler.enableTypeAssertions;
+    // [registerIsCheck] is also called for checked mode checks, so we
+    // need to register checked mode helpers.
+    if (inCheckedMode) {
+      CheckedModeHelper helper = getCheckedModeHelper(type, typeCast: false);
+      if (helper != null) world.addToWorkList(helper.getElement(compiler));
+      // We also need the native variant of the check (for DOM types).
+      helper = getNativeCheckedModeHelper(type, typeCast: false);
+      if (helper != null) world.addToWorkList(helper.getElement(compiler));
+      if (type.isMalformed) {
+        enqueueInResolution(getThrowMalformedSubtypeError(), elements);
+        return;
+      }
+    } else if (type.isMalformed) {
+      registerThrowRuntimeError(elements);
+      return;
+    }
     bool isTypeVariable = type.kind == TypeKind.TYPE_VARIABLE;
-    bool inCheckedMode = compiler.enableTypeAssertions;
-    if (!type.isRaw || isTypeVariable) {
+    if (!type.isRaw || type.containsTypeVariables) {
       enqueueInResolution(getSetRuntimeTypeInfo(), elements);
       enqueueInResolution(getGetRuntimeTypeInfo(), elements);
       enqueueInResolution(getGetRuntimeTypeArgument(), elements);
       if (inCheckedMode) {
         enqueueInResolution(getAssertSubtype(), elements);
       }
       enqueueInResolution(getCheckSubtype(), elements);
       if (isTypeVariable) {
         enqueueInResolution(getCheckSubtypeOfRuntimeType(), elements);
         if (inCheckedMode) {
           enqueueInResolution(getAssertSubtypeOfRuntimeType(), elements);
         }
       }
       world.registerInstantiatedClass(compiler.listClass, elements);
     }
-    // [registerIsCheck] is also called for checked mode checks, so we
-    // need to register checked mode helpers.
-    if (inCheckedMode) {
-      Element e = getCheckedModeHelper(type, typeCast: false);
-      if (e != null) world.addToWorkList(e);
-      // We also need the native variant of the check (for DOM types).
-      e = getNativeCheckedModeHelper(type, typeCast: false);
-      if (e != null) world.addToWorkList(e);
+    if (type is FunctionType) {
+      enqueueInResolution(getCheckFunctionSubtype(), elements);
     }
     if (type.element.isNative()) {
       // We will neeed to add the "$is" and "$as" properties on the
       // JavaScript object prototype, so we make sure
       // [:defineProperty:] is compiled.
       world.addToWorkList(
           compiler.findHelper(const SourceString('defineProperty')));
     }
-  }
+   }
 
   void registerAsCheck(DartType type, TreeElements elements) {
-    Element e = getCheckedModeHelper(type, typeCast: true);
-    enqueueInResolution(e, elements);
+    type = type.unalias(compiler);
+    CheckedModeHelper helper = getCheckedModeHelper(type, typeCast: true);
+    enqueueInResolution(helper.getElement(compiler), elements);
     // We also need the native variant of the check (for DOM types).
-    e = getNativeCheckedModeHelper(type, typeCast: true);
-    enqueueInResolution(e, elements);
+    helper = getNativeCheckedModeHelper(type, typeCast: true);
+    if (helper != null) {
+      enqueueInResolution(helper.getElement(compiler), elements);
+    }
   }
 
   void registerThrowNoSuchMethod(TreeElements elements) {
     enqueueInResolution(getThrowNoSuchMethod(), elements);
   }
 
   void registerThrowRuntimeError(TreeElements elements) {
     enqueueInResolution(getThrowRuntimeError(), elements);
   }
 
@@ skipping 43 matching lines @@
         analyzeTypeArgument(type, argument);
       });
     }
     // TODO(ngeoffray): Also handle T a (in checked mode).
   }
 
   void registerClassUsingVariableExpression(ClassElement cls) {
     rti.classesUsingTypeVariableExpression.add(cls);
   }
 
-  bool needsRti(ClassElement cls) {
+  bool classNeedsRti(ClassElement cls) {
     return rti.classesNeedingRti.contains(cls.declaration) ||
         compiler.enabledRuntimeType;
   }
 
   bool isDefaultNoSuchMethodImplementation(Element element) {
     assert(element.name == Compiler.NO_SUCH_METHOD);
     ClassElement classElement = element.getEnclosingClass();
     return classElement == compiler.objectClass
         || classElement == jsInterceptorClass;
   }
 
   bool isDefaultEqualityImplementation(Element element) {
     assert(element.name == const SourceString('=='));
     ClassElement classElement = element.getEnclosingClass();
     return classElement == compiler.objectClass
         || classElement == jsInterceptorClass
         || classElement == jsNullClass;
   }
 
+  bool methodNeedsRti(FunctionElement function) {
+    return rti.methodsNeedingRti.contains(function) ||
+           compiler.enabledRuntimeType;
+  }
+
+  void enqueue(Enqueuer enqueuer, Element e, TreeElements elements) {
+    enqueuer.addToWorkList(e);
+    elements.registerDependency(e);
+  }
+
   void enqueueInResolution(Element e, TreeElements elements) {
     if (e == null) return;
     ResolutionEnqueuer enqueuer = compiler.enqueuer.resolution;
-    enqueuer.addToWorkList(e);
-    elements.registerDependency(e);
+    enqueue(enqueuer, e, elements);
   }
 
   void registerConstantMap(TreeElements elements) {
     Element e = compiler.findHelper(const SourceString('ConstantMap'));
     if (e != null) {
       compiler.enqueuer.resolution.registerInstantiatedClass(e, elements);
     }
     e = compiler.findHelper(const SourceString('ConstantProtoMap'));
     if (e != null) {
       compiler.enqueuer.resolution.registerInstantiatedClass(e, elements);
@@ skipping 78 matching lines @@
       return element;
     }
   }
 
   /**
    * Returns the checked mode helper that will be needed to do a type check/type
    * cast on [type] at runtime. Note that this method is being called both by
    * the resolver with interface types (int, String, ...), and by the SSA
    * backend with implementation types (JSInt, JSString, ...).
    */
-  Element getCheckedModeHelper(DartType type, {bool typeCast}) {
-    SourceString name = getCheckedModeHelperName(
+  CheckedModeHelper getCheckedModeHelper(DartType type, {bool typeCast}) {
+    return getCheckedModeHelperInternal(
         type, typeCast: typeCast, nativeCheckOnly: false);
-    return compiler.findHelper(name);
   }
 
   /**
    * Returns the native checked mode helper that will be needed to do a type
    * check/type cast on [type] at runtime. If no native helper exists for
    * [type], [:null:] is returned.
    */
-  Element getNativeCheckedModeHelper(DartType type, {bool typeCast}) {
-    SourceString sourceName = getCheckedModeHelperName(
+  CheckedModeHelper getNativeCheckedModeHelper(DartType type, {bool typeCast}) {
+    return getCheckedModeHelperInternal(
         type, typeCast: typeCast, nativeCheckOnly: true);
-    if (sourceName == null) return null;
-    return compiler.findHelper(sourceName);
   }
 
   /**
-   * Returns the name of the type check/type cast helper method for [type]. If
+   * Returns the checked mode helper for the type check/type cast for [type]. If
    * [nativeCheckOnly] is [:true:], only names for native helpers are returned.
    */
-  SourceString getCheckedModeHelperName(DartType type,
-                                        {bool typeCast,
-                                         bool nativeCheckOnly}) {
+  CheckedModeHelper getCheckedModeHelperInternal(DartType type,
+                                                 {bool typeCast,
+                                                  bool nativeCheckOnly}) {
+    assert(type.kind != TypeKind.TYPEDEF);
     Element element = type.element;
     bool nativeCheck = nativeCheckOnly ||
         emitter.nativeEmitter.requiresNativeIsCheck(element);
     if (type.isMalformed) {
       // Check for malformed types first, because the type may be a list type
       // with a malformed argument type.
       if (nativeCheckOnly) return null;
       return typeCast
-          ? const SourceString('malformedTypeCast')
-          : const SourceString('malformedTypeCheck');
+          ? const MalformedCheckedModeHelper(
+              const SourceString('malformedTypeCast'))
+          : const MalformedCheckedModeHelper(
+              const SourceString('malformedTypeCheck'));
     } else if (type == compiler.types.voidType) {
       assert(!typeCast); // Cannot cast to void.
       if (nativeCheckOnly) return null;
-      return const SourceString('voidTypeCheck');
+      return const CheckedModeHelper(const SourceString('voidTypeCheck'));
     } else if (element == jsStringClass || element == compiler.stringClass) {
       if (nativeCheckOnly) return null;
       return typeCast
-          ? const SourceString("stringTypeCast")
-          : const SourceString('stringTypeCheck');
+          ? const CheckedModeHelper(const SourceString("stringTypeCast"))
+          : const CheckedModeHelper(const SourceString('stringTypeCheck'));
     } else if (element == jsDoubleClass || element == compiler.doubleClass) {
       if (nativeCheckOnly) return null;
       return typeCast
-          ? const SourceString("doubleTypeCast")
-          : const SourceString('doubleTypeCheck');
+          ? const CheckedModeHelper(const SourceString("doubleTypeCast"))
+          : const CheckedModeHelper(const SourceString('doubleTypeCheck'));
     } else if (element == jsNumberClass || element == compiler.numClass) {
       if (nativeCheckOnly) return null;
       return typeCast
-          ? const SourceString("numTypeCast")
-          : const SourceString('numTypeCheck');
+          ? const CheckedModeHelper(const SourceString("numTypeCast"))
+          : const CheckedModeHelper(const SourceString('numTypeCheck'));
     } else if (element == jsBoolClass || element == compiler.boolClass) {
       if (nativeCheckOnly) return null;
       return typeCast
-          ? const SourceString("boolTypeCast")
-          : const SourceString('boolTypeCheck');
+          ? const CheckedModeHelper(const SourceString("boolTypeCast"))
+          : const CheckedModeHelper(const SourceString('boolTypeCheck'));
     } else if (element == jsIntClass || element == compiler.intClass) {
       if (nativeCheckOnly) return null;
-      return typeCast ?
-          const SourceString("intTypeCast") :
-          const SourceString('intTypeCheck');
+      return typeCast
+          ? const CheckedModeHelper(const SourceString("intTypeCast"))
+          : const CheckedModeHelper(const SourceString('intTypeCheck'));
     } else if (Elements.isNumberOrStringSupertype(element, compiler)) {
       if (nativeCheck) {
         return typeCast
-            ? const SourceString("numberOrStringSuperNativeTypeCast")
-            : const SourceString('numberOrStringSuperNativeTypeCheck');
+            ? const PropertyCheckedModeHelper(
+                const SourceString("numberOrStringSuperNativeTypeCast"))
+            : const PropertyCheckedModeHelper(
+                const SourceString('numberOrStringSuperNativeTypeCheck'));
       } else {
         return typeCast
-          ? const SourceString("numberOrStringSuperTypeCast")
-          : const SourceString('numberOrStringSuperTypeCheck');
+          ? const PropertyCheckedModeHelper(
+              const SourceString("numberOrStringSuperTypeCast"))
+          : const PropertyCheckedModeHelper(
+              const SourceString('numberOrStringSuperTypeCheck'));
       }
     } else if (Elements.isStringOnlySupertype(element, compiler)) {
       if (nativeCheck) {
         return typeCast
-            ? const SourceString("stringSuperNativeTypeCast")
-            : const SourceString('stringSuperNativeTypeCheck');
+            ? const PropertyCheckedModeHelper(
+                const SourceString("stringSuperNativeTypeCast"))
+            : const PropertyCheckedModeHelper(
+                const SourceString('stringSuperNativeTypeCheck'));
       } else {
         return typeCast
-            ? const SourceString("stringSuperTypeCast")
-            : const SourceString('stringSuperTypeCheck');
+            ? const PropertyCheckedModeHelper(
+                const SourceString("stringSuperTypeCast"))
+            : const PropertyCheckedModeHelper(
+                const SourceString('stringSuperTypeCheck'));
       }
     } else if ((element == compiler.listClass || element == jsArrayClass) &&
                type.isRaw) {
       if (nativeCheckOnly) return null;
       return typeCast
-          ? const SourceString("listTypeCast")
-          : const SourceString('listTypeCheck');
+          ? const CheckedModeHelper(const SourceString("listTypeCast"))
+          : const CheckedModeHelper(const SourceString('listTypeCheck'));
     } else {
       if (Elements.isListSupertype(element, compiler)) {
         if (nativeCheck) {
           return typeCast
-              ? const SourceString("listSuperNativeTypeCast")
-              : const SourceString('listSuperNativeTypeCheck');
+              ? const PropertyCheckedModeHelper(
+                  const SourceString("listSuperNativeTypeCast"))
+              : const PropertyCheckedModeHelper(
+                  const SourceString('listSuperNativeTypeCheck'));
         } else {
           return typeCast
-              ? const SourceString("listSuperTypeCast")
-              : const SourceString('listSuperTypeCheck');
+              ? const PropertyCheckedModeHelper(
+                  const SourceString("listSuperTypeCast"))
+              : const PropertyCheckedModeHelper(
+                  const SourceString('listSuperTypeCheck'));
         }
       } else {
         if (nativeCheck) {
           // TODO(karlklose): can we get rid of this branch when we use
           // interceptors?
           return typeCast
-              ? const SourceString("interceptedTypeCast")
-              : const SourceString('interceptedTypeCheck');
+              ? const PropertyCheckedModeHelper(
+                  const SourceString("interceptedTypeCast"))
+              : const PropertyCheckedModeHelper(
+                  const SourceString('interceptedTypeCheck'));
         } else {
           if (type.kind == TypeKind.INTERFACE && !type.isRaw) {
             return typeCast
-                ? const SourceString('subtypeCast')
-                : const SourceString('assertSubtype');
+                ? const SubtypeCheckedModeHelper(
+                    const SourceString('subtypeCast'))
+                : const SubtypeCheckedModeHelper(
+                    const SourceString('assertSubtype'));
           } else if (type.kind == TypeKind.TYPE_VARIABLE) {
             return typeCast
-                ? const SourceString('subtypeOfRuntimeTypeCast')
-                : const SourceString('assertSubtypeOfRuntimeType');
+                ? const TypeVariableCheckedModeHelper(
+                    const SourceString('subtypeOfRuntimeTypeCast'))
+                : const TypeVariableCheckedModeHelper(
+                    const SourceString('assertSubtypeOfRuntimeType'));
+          } else if (type.kind == TypeKind.FUNCTION) {
+            return typeCast
+                ? const FunctionTypeCheckedModeHelper(
+                    const SourceString('functionSubtypeCast'))
+                : const FunctionTypeCheckedModeHelper(
+                    const SourceString('assertFunctionSubtype'));
           } else {
             return typeCast
-                ? const SourceString('propertyTypeCast')
-                : const SourceString('propertyTypeCheck');
+                ? const PropertyCheckedModeHelper(
+                    const SourceString('propertyTypeCast'))
+                : const PropertyCheckedModeHelper(
+                    const SourceString('propertyTypeCheck'));
           }
         }
       }
     }
   }
 
   Element getExceptionUnwrapper() {
     return compiler.findHelper(const SourceString('unwrapException'));
   }
 
   Element getThrowRuntimeError() {
     return compiler.findHelper(const SourceString('throwRuntimeError'));
   }
 
+  Element getMalformedTypeCheck() {
+    return compiler.findHelper(const SourceString('malformedTypeCheck'));
+  }
+
   Element getThrowMalformedSubtypeError() {
     return compiler.findHelper(
         const SourceString('throwMalformedSubtypeError'));
   }
 
   Element getThrowAbstractClassInstantiationError() {
     return compiler.findHelper(
         const SourceString('throwAbstractClassInstantiationError'));
   }
 
@@ skipping 22 matching lines @@
   }
 
   Element getSetRuntimeTypeInfo() {
     return compiler.findHelper(const SourceString('setRuntimeTypeInfo'));
   }
 
   Element getGetRuntimeTypeInfo() {
     return compiler.findHelper(const SourceString('getRuntimeTypeInfo'));
   }
 
+  Element getComputeSignature() {
+    return compiler.findHelper(const SourceString('computeSignature'));
+  }
+
+  Element getGetRuntimeTypeArguments() {
+    return compiler.findHelper(const SourceString('getRuntimeTypeArguments'));
+  }
+
   Element getGetRuntimeTypeArgument() {
     return compiler.findHelper(const SourceString('getRuntimeTypeArgument'));
   }
 
   Element getRuntimeTypeToString() {
     return compiler.findHelper(const SourceString('runtimeTypeToString'));
   }
 
   Element getCheckSubtype() {
     return compiler.findHelper(const SourceString('checkSubtype'));
   }
 
   Element getAssertSubtype() {
     return compiler.findHelper(const SourceString('assertSubtype'));
   }
 
   Element getCheckSubtypeOfRuntimeType() {
     return compiler.findHelper(const SourceString('checkSubtypeOfRuntimeType'));
   }
 
   Element getAssertSubtypeOfRuntimeType() {
     return compiler.findHelper(
         const SourceString('assertSubtypeOfRuntimeType'));
   }
 
+  Element getCheckFunctionSubtype() {
+    return compiler.findHelper(const SourceString('checkFunctionSubtype'));
+  }
+
   Element getThrowNoSuchMethod() {
     return compiler.findHelper(const SourceString('throwNoSuchMethod'));
   }
 
   Element getCreateRuntimeType() {
     return compiler.findHelper(const SourceString('createRuntimeType'));
   }
 
   Element getFallThroughError() {
     return compiler.findHelper(const SourceString("getFallThroughError"));
@@ skipping 47 matching lines @@
  }
 
   void registerStaticUse(Element element, Enqueuer enqueuer) {
     if (element == disableTreeShakingMarker) {
       enqueuer.enqueueEverything();
       compiler.disableTypeInferenceForMirrors = true;
     } else if (element == preserveNamesMarker) {
     }
   }
 }