Revert "Revert "First step towards having patch files for generic libraries.""

lib/compiler/implementation/compiler.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.
 
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
 final bool REPORT_EXCESS_RESOLUTION = false;
@@ skipping 489 matching lines @@
     scanner.importLibrary(interceptorsLibrary, coreLibrary, null);
     addForeignFunctions(jsHelperLibrary);
     addForeignFunctions(interceptorsLibrary);
 
     libraries['dart:core'] = coreLibrary;
     libraries['dart:coreimpl'] = coreImplLibrary;
 
     assertMethod = coreLibrary.find(const SourceString('assert'));
 
     initializeSpecialClasses();
+
+    patchDartLibrary(coreLibrary, 'core');
+    patchDartLibrary(coreImplLibrary, 'coreimpl');
   }
 
+  void patchDartLibrary(LibraryElement library, String dartLibraryPath) {
+    if (library.isPatched) return;
+    Uri patchUri = resolvePatchUri(dartLibraryPath);
+    if (patchUri !== null) {
+      // TODO(lrn): Use a different parser to allow for "patch" annotations.
+      // For now just assume everything in the patch library is a patch
+      // function.
+      LibraryElement patchLibrary = scanner.loadLibrary(patchUri, null);
+      applyLibraryPatch(library, patchLibrary);
+    }
+  }
+
+  void applyLibraryPatch(LibraryElement library, LibraryElement patch) {
+    Link<Element> patches = patch.topLevelElements;
+    while (!patches.isEmpty()) {
+      Element patchElement = patches.head;
+      Element originalElement = library.elements[patchElement.name];
+      if (originalElement !== null) {
+        // Assume that we are patching if the original exists.
+        if (originalElement is! FunctionElement) {
+          // TODO(lrn): Handle class declarations too.
+          internalError("Can only patch functions", element: originalElement);
+        }
+        // TODO(lrn): Abort if the original isn't marked external, when
+        // that is added to the language.
+        if (patchElement is! FunctionElement ||
+            !patchSignatureMatches(originalElement, patchElement)) {
+          internalError("Can only patch functions with matching signatures",
+                        element: originalElement);
+        }
+        applyFunctionPatch(originalElement, patchElement);
+      } else {
+        // TODO(lrn): Allow adding private elements to the original library.
+      }
+      patches = patches.tail;
+    }
+    library.patch = patch;
+  }
+
+  bool patchSignatureMatches(FunctionElement original, FunctionElement patch) {
+    // TODO(lrn): Check that patches actually match the signature of
+    // the function it's patching.
+    return true;
+  }
+
+  void applyFunctionPatch(FunctionElement element,
+                          FunctionElement patchElement) {
+    // Don't just assign the patch field. This also updates the cachedNode.
+    if (element.isPatched) {
+      internalError("Trying to patch a function more than once.",
+                    element: element);
+    }
+    if (element.cachedNode !== null) {
+      internalError("Trying to patch an already compiled function.",
+                    element: element);
+    }
+    element.setPatch(patchElement);
+  }
+
+  /**
+   * Get an [Uri] pointing to a patch for the dart: library with
+   * the given path. Returns null if there is no patch.
+   */
+  abstract Uri resolvePatchUri(String dartLibraryPath);
+
   /** Define the JS helper functions in the given library. */
   void addForeignFunctions(LibraryElement library) {
     library.define(new ForeignElement(
         const SourceString('JS'), library), this);
     library.define(new ForeignElement(
         const SourceString('UNINTERCEPTED'), library), this);
     library.define(new ForeignElement(
         const SourceString('JS_HAS_EQUALS'), library), this);
     library.define(new ForeignElement(
         const SourceString('JS_CURRENT_ISOLATE'), library), this);
@@ skipping 372 matching lines @@
                      f(int beginOffset, int endOffset)) {
     final beginOffset = begin.charOffset;
     final endOffset = end.charOffset + end.slowCharCount;
 
     // [begin] and [end] might be the same for the same empty token. This
     // happens for instance when scanning '$$'.
     assert(endOffset >= beginOffset);
     return f(beginOffset, endOffset);
   }
 }