Improve recovery from compile-time errors.

pkg/front_end/lib/src/fasta/loader.dart

 // Copyright (c) 2016, 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 fasta.loader;
 
 import 'dart:async' show Future;
 
 import 'dart:collection' show Queue;
 
 import 'builder/builder.dart' show Builder, LibraryBuilder;
 
 import 'errors.dart' show InputError, firstSourceUri, printUnexpected;
 
 import 'target_implementation.dart' show TargetImplementation;
 
 import 'ticker.dart' show Ticker;
 
 abstract class Loader<L> {
   final Map<Uri, LibraryBuilder> builders = <Uri, LibraryBuilder>{};
 
   final Queue<LibraryBuilder> unparsedLibraries = new Queue<LibraryBuilder>();
 
   final List<L> libraries = <L>[];
 
   final TargetImplementation target;
 
-  final List<InputError> errors = <InputError>[];
+  /// List of all handled compile-time errors seen so far by libraries loaded
+  /// by this loader.
+  ///
+  /// A handled error is an error that has been added to the generated AST
+  /// already, for example, as a throw expression.
+  final List<InputError> handledErrors = <InputError>[];
+
+  /// List of all unhandled compile-time errors seen so far by libraries loaded
+  /// by this loader.
+  ///
+  /// An unhandled error is an error that hasn't been handled, see
+  /// [handledErrors].
+  final List<InputError> unhandledErrors = <InputError>[];
 
   LibraryBuilder coreLibrary;
 
   LibraryBuilder first;
 
   int byteCount = 0;
 
   Uri currentUriForCrashReporting;
 
   Loader(this.target);
@@ skipping 39 matching lines @@
       first ??= library;
       if (library.loader == this) {
         unparsedLibraries.addLast(library);
       }
       return library;
     });
     if (accessor != null &&
         uri.scheme == "dart" &&
         uri.path.startsWith("_") &&
         accessor.uri.scheme != "dart") {
-      const String message = "Can't access platform private library.";
-      printUnexpected(accessor.fileUri, charOffset, message);
-      errors.add(new InputError(accessor.fileUri, charOffset, message));
+      accessor.addCompileTimeError(
+          charOffset, "Can't access platform private library.");
     }
     return builder;
   }
 
   void ensureCoreLibrary() {
     if (coreLibrary == null) {
       read(Uri.parse("dart:core"), -1);
       assert(coreLibrary != null);
     }
   }
@@ skipping 38 matching lines @@
 ${format(byteCount / ms, 3, 12)} bytes/ms, and
 ${format(ms / libraryCount, 3, 12)} ms/compilation unit.""");
     });
   }
 
   Future<Null> buildOutline(covariant LibraryBuilder library);
 
   /// Builds all the method bodies found in the given [library].
   Future<Null> buildBody(covariant LibraryBuilder library);
 
-  List<InputError> collectCompileTimeErrors() {
-    List<InputError> errors = <InputError>[]..addAll(this.errors);
-    for (LibraryBuilder library in builders.values) {
-      if (library.loader == this) {
-        errors.addAll(library.compileTimeErrors);
-      }
+  /// Register [message] as a compile-time error.
+  ///
+  /// If [silent] is true, no error is printed as it is assumed the error has
+  /// been previously reported.
+  ///
+  /// If [wasHandled] is true, this error is added to [handledErrors],
+  /// otherwise it is added to [unhandledErrors].
+  void addCompileTimeError(Uri fileUri, int charOffset, Object message,
+      {bool silent: false, bool wasHandled: false}) {
+    if (!silent) {
+      printUnexpected(fileUri, charOffset, message);
     }
-    return errors;
+    (wasHandled ? handledErrors : unhandledErrors)
+        .add(new InputError(fileUri, charOffset, message));
   }
 
   Builder getAbstractClassInstantiationError() {
     return target.getAbstractClassInstantiationError(this);
   }
 
   Builder getCompileTimeError() => target.getCompileTimeError(this);
 
   Builder getDuplicatedFieldInitializerError() {
     return target.getDuplicatedFieldInitializerError(this);
   }
 
   Builder getFallThroughError() => target.getFallThroughError(this);
 
   Builder getNativeAnnotation() => target.getNativeAnnotation(this);
 }
 
 String format(double d, int fractionDigits, int width) {
   return d.toStringAsFixed(fractionDigits).padLeft(width);
 }