Improve parser error recovery.

dart/sdk/lib/_internal/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.
 
 part of dart2js;
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
@@ skipping 1246 matching lines @@
               MessageKind.GENERIC,
               {'text': "Could not find '$MAIN'."});
         } else if (!analyzeAll) {
           reportFatalError(mainApp, MessageKind.GENERIC,
               {'text': "Could not find '$MAIN'. "
                        "No source will be analyzed. "
                        "Use '--analyze-all' to analyze all code in the "
                        "library."});
         }
       } else {
-        if (main.isErroneous) {
+        if (main.isErroneous && main.isSynthesized) {
           reportFatalError(main, MessageKind.GENERIC,
               {'text': "Cannot determine which '$MAIN' to use."});
         } else if (!main.isFunction) {
           reportFatalError(main, MessageKind.GENERIC,
               {'text': "'$MAIN' is not a function."});
         }
         mainFunction = main;
         FunctionSignature parameters = mainFunction.computeSignature(this);
         if (parameters.parameterCount > 2) {
           int index = 0;
@@ skipping 367 matching lines @@
     }
     return SourceSpan.withCharacterOffsets(begin, end,
       (beginOffset, endOffset) => new SourceSpan(uri, beginOffset, endOffset));
   }
 
   SourceSpan spanFromNode(Node node) {
     return spanFromTokens(node.getBeginToken(), node.getEndToken());
   }
 
   SourceSpan spanFromElement(Element element) {
-    if (Elements.isErroneousElement(element)) {
+    while (element != null && element.isSynthesized) {
       element = element.enclosingElement;
     }
-    if (element.position == null &&
+    if (element != null &&
+        element.position == null &&
         !element.isLibrary &&
         !element.isCompilationUnit) {
       // Sometimes, the backend fakes up elements that have no
       // position. So we use the enclosing element instead. It is
       // not a good error location, but cancel really is "internal
       // error" or "not implemented yet", so the vicinity is good
       // enough for now.
       element = element.enclosingElement;
       // TODO(ahe): I plan to overhaul this infrastructure anyways.
     }
@@ skipping 327 matching lines @@
   static NullSink outputProvider(String name, String extension) {
     return new NullSink('$name.$extension');
   }
 }
 
 /// Information about suppressed warnings and hints for a given library.
 class SuppressionInfo {
   int warnings = 0;
   int hints = 0;
 }