Improve compile-time error handling.

pkg/front_end/lib/src/fasta/testing/kernel_chain.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.md file.
 
 // TODO(ahe): Copied from closure_conversion branch of kernel, remove this file
 // when closure_conversion is merged with master.
 
 library kernel.testing.kernel_chain;
 
 import 'dart:async' show
@@ skipping 137 matching lines @@
         ignoreRedirectingFactories: false, dartSdk: dartSdk);
   }
 
   static Future<TestContext> create(Chain suite,
       Map<String, String> environment,
       TestContextConstructor constructor) async {
     Uri sdk = await computePatchedSdk();
     Uri vm = computeDartVm(sdk);
     Uri packages = Uri.base.resolve(".packages");
     bool strongMode = false;
-    bool updateExpectations = environment["updateExpectations"] != "false";
+    bool updateExpectations = environment["updateExpectations"] == "true";
     return constructor(suite, environment, sdk, vm, packages, strongMode,
         createDartSdk(sdk.toFilePath(), strongMode: strongMode),
         updateExpectations);
   }
 }
 
 class Kernel extends Step<TestDescription, Program, TestContext> {
   const Kernel();
 
   String get name => "kernel";
@@ skipping 56 matching lines @@
   }
 }
 
 class MatchExpectation extends Step<Program, Program, dynamic> {
   final String suffix;
 
   // TODO(ahe): This is true by default which doesn't match well with the class
   // name.
   final bool updateExpectations;
 
-  const MatchExpectation(this.suffix, {this.updateExpectations: true});
+  const MatchExpectation(this.suffix, {this.updateExpectations: false});
 
   String get name => "match expectations";
 
   Future<Result<Program>> run(Program program, _) async {
     Library library = program.libraries.firstWhere(
         (Library library) => library.importUri.scheme != "dart");
     Uri uri = library.importUri;
     StringBuffer buffer = new StringBuffer();
     new Printer(buffer).writeLibraryFile(library);
 
-    bool updateExpectations = this.updateExpectations;
-    if (uri.path.contains("/test/fasta/rasta/")) {
-      // TODO(ahe): Remove this. Short term, we don't want to automatically
-      // update rasta expectations, as we have too many failures.
-      updateExpectations = false;
-    }
     File expectedFile = new File("${uri.toFilePath()}$suffix");
     if (await expectedFile.exists()) {
       String expected = await expectedFile.readAsString();
       if (expected.trim() != "$buffer".trim()) {
         if (!updateExpectations) {
           String diff = await runDiff(expectedFile.uri, "$buffer");
           return fail(null, "$uri doesn't match ${expectedFile.uri}\n$diff");
         }
       } else {
         return pass(program);
@@ skipping 119 matching lines @@
 
 Future openWrite(Uri uri, f(IOSink sink)) async {
   IOSink sink = new File.fromUri(uri).openWrite();
   try {
     await f(sink);
   } finally {
     await sink.close();
   }
   print("Wrote $uri");
 }