Report compile-time errors on cyclic hierarchies.

pkg/front_end/lib/src/fasta/source/source_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.source_loader;
 
 import 'dart:async' show Future;
 
 import 'dart:io' show FileSystemException;
 
 import 'dart:typed_data' show Uint8List;
 
 import 'package:kernel/ast.dart' show Program;
 
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
 
 import 'package:kernel/core_types.dart' show CoreTypes;
 
 import '../builder/builder.dart' show Builder, ClassBuilder, LibraryBuilder;
 
 import '../compiler_context.dart' show CompilerContext;
 
 import '../errors.dart' show inputError;
 
 import '../export.dart' show Export;
 
 import '../loader.dart' show Loader;
 
-import '../messages.dart' show warning;
-
 import '../parser/class_member_parser.dart' show ClassMemberParser;
 
 import '../scanner.dart' show ErrorToken, ScannerResult, Token, scan;
 
 import '../scanner/io.dart' show readBytesFromFile;
 
 import '../target_implementation.dart' show TargetImplementation;
 
 import 'diet_listener.dart' show DietListener;
 
@@ skipping 288 matching lines @@
     realCycles.forEach((ClassBuilder cls, Set<ClassBuilder> cycles) {
       target.breakCycle(cls);
       if (reported.add(cls)) {
         List<ClassBuilder> involved = <ClassBuilder>[];
         for (ClassBuilder cls in cycles) {
           if (realCycles.containsKey(cls)) {
             involved.add(cls);
             reported.add(cls);
           }
         }
-        warning(
-            cls.fileUri,
+        cls.addCompileTimeError(
             cls.charOffset,
             "'${cls.name}' is a supertype of "
             "itself via '${involved.map((c) => c.name).join(' ')}'.");
       }
     });
     ticker.logMs("Found cycles");
   }
 
   void buildProgram() {
     builders.forEach((Uri uri, LibraryBuilder library) {
@@ skipping 14 matching lines @@
   void checkOverrides(List<SourceClassBuilder> sourceClasses) {
     assert(hierarchy != null);
     for (SourceClassBuilder builder in sourceClasses) {
       builder.checkOverrides(hierarchy);
     }
     ticker.logMs("Checked overrides");
   }
 
   List<Uri> getDependencies() => sourceBytes.keys.toList();
 }