Add Source.getTextLine and use it to display source snippets in error messages.

pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart

 // Copyright (c) 2015, 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 dart2js.js_emitter.startup_emitter.model_emitter;
 
 import 'dart:convert' show JsonEncoder;
 
 import 'package:js_runtime/shared/embedded_names.dart'
     show
@@ skipping 20 matching lines @@
         TYPES;
 
 import '../../../compiler_new.dart';
 import '../../common.dart';
 import '../../compiler.dart' show Compiler;
 import '../../constants/values.dart' show ConstantValue, FunctionConstantValue;
 import '../../common_elements.dart' show CommonElements;
 import '../../elements/elements.dart' show ClassElement, MethodElement;
 import '../../hash/sha1.dart' show Hasher;
 import '../../io/code_output.dart';
-import '../../io/line_column_provider.dart' show LineColumnCollector;
+import '../../io/location_provider.dart' show LocationCollector;
 import '../../io/source_map_builder.dart' show SourceMapBuilder;
 import '../../js/js.dart' as js;
 import '../../js_backend/js_backend.dart'
     show JavaScriptBackend, Namer, ConstantEmitter;
 import '../constant_ordering.dart' show deepCompareConstants;
 import '../headers.dart';
 import '../js_emitter.dart' show NativeEmitter;
 import '../js_emitter.dart' show buildTearOffCode, NativeGenerator;
 import '../model.dart';
 
@@ skipping 183 matching lines @@
         'self.#deferredInitializers = '
         'self.#deferredInitializers || Object.create(null);',
         {'deferredInitializers': deferredInitializersGlobal});
   }
 
   // Writes the given [fragment]'s [code] into a file.
   //
   // Updates the shared [outputBuffers] field with the output.
   void writeMainFragment(MainFragment fragment, js.Statement code,
       {bool isSplit}) {
-    LineColumnCollector lineColumnCollector;
+    LocationCollector locationCollector;
     List<CodeOutputListener> codeOutputListeners;
     if (shouldGenerateSourceMap) {
-      lineColumnCollector = new LineColumnCollector();
-      codeOutputListeners = <CodeOutputListener>[lineColumnCollector];
+      locationCollector = new LocationCollector();
+      codeOutputListeners = <CodeOutputListener>[locationCollector];
     }
 
     CodeOutput mainOutput = new StreamCodeOutput(
         compiler.outputProvider('', 'js', OutputType.js), codeOutputListeners);
     outputBuffers[fragment] = mainOutput;
 
     js.Program program = new js.Program([
       buildGeneratedBy(),
       new js.Comment(HOOKS_API_USAGE),
       isSplit ? buildDeferredInitializerGlobal() : new js.Block.empty(),
       code
     ]);
 
     mainOutput.addBuffer(
         js.createCodeBuffer(program, compiler, monitor: compiler.dumpInfoTask));
 
     if (shouldGenerateSourceMap) {
       mainOutput.add(SourceMapBuilder.generateSourceMapTag(
           compiler.options.sourceMapUri, compiler.options.outputUri));
     }
 
     mainOutput.close();
 
     if (shouldGenerateSourceMap) {
       SourceMapBuilder.outputSourceMap(
           mainOutput,
-          lineColumnCollector,
+          locationCollector,
           '',
           compiler.options.sourceMapUri,
           compiler.options.outputUri,
           compiler.outputProvider);
     }
   }
 
   // Writes the given [fragment]'s [code] into a file.
   //
   // Returns the deferred fragment's hash.
   //
   // Updates the shared [outputBuffers] field with the output.
   String writeDeferredFragment(DeferredFragment fragment, js.Expression code) {
     List<CodeOutputListener> outputListeners = <CodeOutputListener>[];
     Hasher hasher = new Hasher();
     outputListeners.add(hasher);
 
-    LineColumnCollector lineColumnCollector;
+    LocationCollector locationCollector;
     if (shouldGenerateSourceMap) {
-      lineColumnCollector = new LineColumnCollector();
-      outputListeners.add(lineColumnCollector);
+      locationCollector = new LocationCollector();
+      outputListeners.add(locationCollector);
     }
 
     String hunkPrefix = fragment.outputFileName;
 
     CodeOutput output = new StreamCodeOutput(
         compiler.outputProvider(
             hunkPrefix, deferredExtension, OutputType.jsPart),
         outputListeners);
 
     outputBuffers[fragment] = output;
@@ skipping 42 matching lines @@
 
       if (outputUri != null) {
         List<String> partSegments = outputUri.pathSegments.toList();
         partSegments[partSegments.length - 1] = hunkFileName;
         partUri =
             compiler.options.outputUri.replace(pathSegments: partSegments);
       }
 
       output.add(SourceMapBuilder.generateSourceMapTag(mapUri, partUri));
       output.close();
-      SourceMapBuilder.outputSourceMap(output, lineColumnCollector, partName,
+      SourceMapBuilder.outputSourceMap(output, locationCollector, partName,
           mapUri, partUri, compiler.outputProvider);
     } else {
       output.close();
     }
 
     return hash;
   }
 
   /// Writes a mapping from library-name to hunk files.
   ///
   /// The output is written into a separate file that can be used by outside
   /// tools.
   void writeDeferredMap() {
     Map<String, dynamic> mapping = new Map<String, dynamic>();
     // Json does not support comments, so we embed the explanation in the
     // data.
     mapping["_comment"] = "This mapping shows which compiled `.js` files are "
         "needed for a given deferred library import.";
     mapping.addAll(compiler.deferredLoadTask.computeDeferredMap());
     compiler.outputProvider(
         compiler.options.deferredMapUri.path, '', OutputType.info)
       ..add(const JsonEncoder.withIndent("  ").convert(mapping))
       ..close();
   }
 }