Avoid patching in dart2dart.

pkg/compiler/lib/src/js_backend/patch_resolver.dart

Index: pkg/compiler/lib/src/js_backend/patch_resolver.dart
diff --git a/pkg/compiler/lib/src/js_backend/patch_resolver.dart b/pkg/compiler/lib/src/js_backend/patch_resolver.dart
new file mode 100644
index 0000000000000000000000000000000000000000..d538fe501bbbff7d71f931a308e3ff12423e922c
--- /dev/null
+++ b/pkg/compiler/lib/src/js_backend/patch_resolver.dart
@@ -0,0 +1,159 @@
+// Copyright (c) 2014, 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 dart2js.js_backend.patch_resolver;
+
+import '../dart2jslib.dart';
+import '../dart_types.dart';
+import '../elements/elements.dart';
+import '../elements/modelx.dart';
+import '../resolution/resolution.dart';
+import '../tree/tree.dart';
+import '../util/util.dart';
+
+class PatchResolverTask extends CompilerTask {
+  PatchResolverTask(Compiler compiler) : super(compiler);
+
+  String get name => 'JavaScript patch resolver';
+
+  FunctionElement resolveExternalFunction(FunctionElementX element) {
+    if (element.isPatched) {
+      FunctionElementX patch = element.patch;
+      compiler.withCurrentElement(patch, () {
+        patch.parseNode(compiler);
+        patch.computeType(compiler);
+      });
+      checkMatchingPatchSignatures(element, patch);
+      element = patch;
+      ResolverTask.processAsyncMarker(compiler, element);
+    } else {
+      compiler.reportError(
+         element, MessageKind.PATCH_EXTERNAL_WITHOUT_IMPLEMENTATION);
+    }
+    return element;
+  }
+
+  void checkMatchingPatchParameters(FunctionElement origin,
+                                    Link<Element> originParameters,
+                                    Link<Element> patchParameters) {
+    while (!originParameters.isEmpty) {
+      ParameterElementX originParameter = originParameters.head;
+      ParameterElementX patchParameter = patchParameters.head;
+      // TODO(johnniwinther): Remove the conditional patching when we never
+      // resolve the same method twice.
+      if (!originParameter.isPatched) {
+        originParameter.applyPatch(patchParameter);
+      } else {
+        assert(invariant(origin, originParameter.patch == patchParameter,
+               message: "Inconsistent repatch of $originParameter."));
+      }
+      DartType originParameterType = originParameter.computeType(compiler);
+      DartType patchParameterType = patchParameter.computeType(compiler);
+      if (originParameterType != patchParameterType) {
+        compiler.reportError(
+            originParameter.parseNode(compiler),
+            MessageKind.PATCH_PARAMETER_TYPE_MISMATCH,
+            {'methodName': origin.name,
+             'parameterName': originParameter.name,
+             'originParameterType': originParameterType,
+             'patchParameterType': patchParameterType});
+        compiler.reportInfo(patchParameter,
+            MessageKind.PATCH_POINT_TO_PARAMETER,
+            {'parameterName': patchParameter.name});
+      } else {
+        // Hack: Use unparser to test parameter equality. This only works
+        // because we are restricting patch uses and the approach cannot be used
+        // elsewhere.
+
+        // The node contains the type, so there is a potential overlap.
+        // Therefore we only check the text if the types are identical.
+        String originParameterText =
+            originParameter.parseNode(compiler).toString();
+        String patchParameterText =
+            patchParameter.parseNode(compiler).toString();
+        if (originParameterText != patchParameterText
+            // We special case the list constructor because of the
+            // optional parameter.
+            && origin != compiler.unnamedListConstructor) {
+          compiler.reportError(
+              originParameter.parseNode(compiler),
+              MessageKind.PATCH_PARAMETER_MISMATCH,
+              {'methodName': origin.name,
+               'originParameter': originParameterText,
+               'patchParameter': patchParameterText});
+          compiler.reportInfo(patchParameter,
+              MessageKind.PATCH_POINT_TO_PARAMETER,
+              {'parameterName': patchParameter.name});
+        }
+      }
+
+      originParameters = originParameters.tail;
+      patchParameters = patchParameters.tail;
+    }
+  }
+
+  void checkMatchingPatchSignatures(FunctionElement origin,
+                                    FunctionElement patch) {
+    // TODO(johnniwinther): Show both origin and patch locations on errors.
+    FunctionExpression originTree = origin.node;
+    FunctionSignature originSignature = origin.functionSignature;
+    FunctionExpression patchTree = patch.node;
+    FunctionSignature patchSignature = patch.functionSignature;
+
+    if (originSignature.type.returnType != patchSignature.type.returnType) {
+      compiler.withCurrentElement(patch, () {
+        Node errorNode =
+            patchTree.returnType != null ? patchTree.returnType : patchTree;
+        compiler.reportError(
+            errorNode, MessageKind.PATCH_RETURN_TYPE_MISMATCH,
+            {'methodName': origin.name,
+             'originReturnType': originSignature.type.returnType,
+             'patchReturnType': patchSignature.type.returnType});
+      });
+    }
+    if (originSignature.requiredParameterCount !=
+        patchSignature.requiredParameterCount) {
+      compiler.withCurrentElement(patch, () {
+        compiler.reportError(
+            patchTree,
+            MessageKind.PATCH_REQUIRED_PARAMETER_COUNT_MISMATCH,
+            {'methodName': origin.name,
+             'originParameterCount': originSignature.requiredParameterCount,
+             'patchParameterCount': patchSignature.requiredParameterCount});
+      });
+    } else {
+      checkMatchingPatchParameters(origin,
+                                   originSignature.requiredParameters,
+                                   patchSignature.requiredParameters);
+    }
+    if (originSignature.optionalParameterCount != 0 &&
+        patchSignature.optionalParameterCount != 0) {
+      if (originSignature.optionalParametersAreNamed !=
+          patchSignature.optionalParametersAreNamed) {
+        compiler.withCurrentElement(patch, () {
+          compiler.reportError(
+              patchTree,
+              MessageKind.PATCH_OPTIONAL_PARAMETER_NAMED_MISMATCH,
+              {'methodName': origin.name});
+        });
+      }
+    }
+    if (originSignature.optionalParameterCount !=
+        patchSignature.optionalParameterCount) {
+      compiler.withCurrentElement(patch, () {
+        compiler.reportError(
+            patchTree,
+            MessageKind.PATCH_OPTIONAL_PARAMETER_COUNT_MISMATCH,
+            {'methodName': origin.name,
+             'originParameterCount': originSignature.optionalParameterCount,
+             'patchParameterCount': patchSignature.optionalParameterCount});
+      });
+    } else {
+      checkMatchingPatchParameters(origin,
+                                   originSignature.optionalParameters,
+                                   patchSignature.optionalParameters);
+    }
+  }
+
+}