Testable patch parser.

dart/sdk/lib/_internal/compiler/implementation/patch_parser.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.
 
 /**
  * This library contains the infrastructure to parse and integrate patch files.
  *
  * Three types of elements can be patched: [LibraryElement], [ClassElement],
  * [FunctionElement]. Patches are introduced in patch libraries which are loaded
  * together with the corresponding origin library. Which libraries that are
@@ skipping 311 matching lines @@
     */
   bool allowLibraryTags() => true;
 
   void addLibraryTag(tree.LibraryTag tag) {
     super.addLibraryTag(tag);
     imports.addLast(tag);
   }
 
   void pushElement(Element patch) {
     if (isMemberPatch || (isClassPatch && patch is ClassElement)) {
-      // Apply patch.
       patch.addMetadata(popMetadata());
-      LibraryElement originLibrary = compilationUnitElement.getLibrary();
-      assert(originLibrary.isPatched);
-      Element origin = originLibrary.localLookup(patch.name);
-      _patchElement(listener, origin, patch);
+      applyPatch(patch);
     }
     super.pushElement(patch);
   }
+
+  void applyPatch(Element patch) {
+    LibraryElement originLibrary = compilationUnitElement.getLibrary();
+    assert(originLibrary.isPatched);
+    Element origin = originLibrary.localLookup(patch.name);
+    _patchElement(listener, origin, patch);
+  }
 }
 
 /**
  * Extension of [MemberListener] for parsing patch class bodies.
  */
 class PatchMemberListener extends MemberListener implements PatchListener {
   bool isMemberPatch = false;
   bool isClassPatch = false;
   PatchMemberListener(leg.DiagnosticListener listener,
                       Element enclosingElement)
@@ skipping 32 matching lines @@
 
 // TODO(ahe): Get rid of this class.
 class PatchMetadataAnnotation extends MetadataAnnotationX {
   final leg.Constant value = null;
 
   PatchMetadataAnnotation() : super(STATE_DONE);
 
   Token get beginToken => null;
 }
 
+void patchElement(leg.DiagnosticListener listener,
+                  Element origin,
+                  Element patch) {
+  _patchElement(listener, origin, patch);
+}
+
 void _patchElement(leg.DiagnosticListener listener,
                    Element origin,
                    Element patch) {
   if (origin == null) {
     listener.reportMessage(
         listener.spanFromSpannable(patch),
         leg.MessageKind.PATCH_NON_EXISTING.error([patch.name]),
         api.Diagnostic.ERROR);
     return;
   }
@@ skipping 179 matching lines @@
 }
 
 bool _isPatchElement(Element element) {
   // TODO(lrn): More checks needed if we introduce metadata for real.
   // In that case, it must have the identifier "native" as metadata.
   for (Link link = element.metadata; !link.isEmpty; link = link.tail) {
     if (link.head is PatchMetadataAnnotation) return true;
   }
   return false;
 }
+
+bool isPatchElement(Element element) => _isPatchElement(element);