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

tests/compiler/dart2js/sourcemaps/diff.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 sourcemap.diff;
 
 import 'package:compiler/src/io/source_file.dart';
 
 import 'html_parts.dart';
 import 'output_structure.dart';
@@ skipping 429 matching lines @@
       addSkewedEntity(index, parent.getChild(i));
     }
   }
 
   /// Adds the members of the [classes] aligned.
   void addMatchingContainers(List<OutputEntity> classes) {
     addLines(DiffKind.MATCHING, classes.map((c) => c.header).toList());
     align(classes[0].children, classes[1].children,
         match: (a, b) => a.name == b.name,
         handleSkew: (int listIndex, Interval childRange) {
-      addSkewedChildren(listIndex, classes[listIndex], childRange);
-    }, handleMatched: (List<int> indices) {
-      List<BasicEntity> entities = [
-        classes[0].getChild(indices[0]),
-        classes[1].getChild(indices[1])
-      ];
-      if (entities.every((e) => e is Statics)) {
-        addMatchingContainers(entities);
-      } else {
-        addLines(DiffKind.MATCHING, entities.map((e) => e.interval).toList(),
-            codeSourceFromEntities(entities));
-      }
-    }, handleUnmatched: (List<int> indices) {
-      List<Interval> intervals = [
-        classes[0].getChild(indices[0]).interval,
-        classes[1].getChild(indices[1]).interval
-      ];
-      addLines(DiffKind.UNMATCHED, intervals);
-    });
+          addSkewedChildren(listIndex, classes[listIndex], childRange);
+        },
+        handleMatched: (List<int> indices) {
+          List<BasicEntity> entities = [
+            classes[0].getChild(indices[0]),
+            classes[1].getChild(indices[1])
+          ];
+          if (entities.every((e) => e is Statics)) {
+            addMatchingContainers(entities);
+          } else {
+            addLines(
+                DiffKind.MATCHING,
+                entities.map((e) => e.interval).toList(),
+                codeSourceFromEntities(entities));
+          }
+        },
+        handleUnmatched: (List<int> indices) {
+          List<Interval> intervals = [
+            classes[0].getChild(indices[0]).interval,
+            classes[1].getChild(indices[1]).interval
+          ];
+          addLines(DiffKind.UNMATCHED, intervals);
+        });
     addLines(DiffKind.MATCHING, classes.map((c) => c.footer).toList());
   }
 
   /// Adds the library blocks in [indices] from the corresponding
   /// [OutputStructure]s, aligning their content.
   void addMatchingBlocks(List<int> indices) {
     List<LibraryBlock> blocks = [
       structures[0].getChild(indices[0]),
       structures[1].getChild(indices[1])
     ];
 
     addLines(DiffKind.MATCHING, blocks.map((b) => b.header).toList());
     align(blocks[0].children, blocks[1].children,
         match: (a, b) => a.name == b.name,
         handleSkew: (int listIndex, Interval childRange) {
-      addSkewedChildren(listIndex, blocks[listIndex], childRange);
-    }, handleMatched: (List<int> indices) {
-      List<BasicEntity> entities = [
-        blocks[0].getChild(indices[0]),
-        blocks[1].getChild(indices[1])
-      ];
-      if (entities.every((e) => e is LibraryClass)) {
-        addMatchingContainers(entities);
-      } else {
-        addLines(DiffKind.MATCHING, entities.map((e) => e.interval).toList(),
-            codeSourceFromEntities(entities));
-      }
-    }, handleUnmatched: (List<int> indices) {
-      List<Interval> intervals = [
-        blocks[0].getChild(indices[0]).interval,
-        blocks[1].getChild(indices[1]).interval
-      ];
-      addLines(DiffKind.UNMATCHED, intervals);
-    });
+          addSkewedChildren(listIndex, blocks[listIndex], childRange);
+        },
+        handleMatched: (List<int> indices) {
+          List<BasicEntity> entities = [
+            blocks[0].getChild(indices[0]),
+            blocks[1].getChild(indices[1])
+          ];
+          if (entities.every((e) => e is LibraryClass)) {
+            addMatchingContainers(entities);
+          } else {
+            addLines(
+                DiffKind.MATCHING,
+                entities.map((e) => e.interval).toList(),
+                codeSourceFromEntities(entities));
+          }
+        },
+        handleUnmatched: (List<int> indices) {
+          List<Interval> intervals = [
+            blocks[0].getChild(indices[0]).interval,
+            blocks[1].getChild(indices[1]).interval
+          ];
+          addLines(DiffKind.UNMATCHED, intervals);
+        });
     addLines(DiffKind.MATCHING, blocks.map((b) => b.footer).toList());
   }
 
   /// Adds the lines of the blocks in [indices] from the corresponding
   /// [OutputStructure]s.
   void addUnmatchedBlocks(List<int> indices) {
     List<LibraryBlock> blocks = [
       structures[0].getChild(indices[0]),
       structures[1].getChild(indices[1])
     ];
@@ skipping 20 matching lines @@
   List<HtmlPart> codeLinesFromCodeSource(CodeSource codeSource) {
     List<HtmlPart> lines = <HtmlPart>[];
     SourceFile sourceFile = sourceFileManager.getSourceFile(codeSource.uri);
     String elementName = codeSource.name;
     HtmlLine line = new HtmlLine();
     line.htmlParts.add(new ConstHtmlPart('<span class="comment">'));
     line.htmlParts.add(new HtmlText('${elementName}: ${sourceFile.filename}'));
     line.htmlParts.add(new ConstHtmlPart('</span>'));
     lines.add(line);
     if (codeSource.begin != null) {
-      int startLine = sourceFile.getLine(codeSource.begin);
-      int endLine = sourceFile.getLine(codeSource.end) + 1;
+      int startLine = sourceFile.getLocation(codeSource.begin).line - 1;
+      int endLine = sourceFile.getLocation(codeSource.end).line;
       for (CodeLine codeLine in convertAnnotatedCodeToCodeLines(
           sourceFile.slowText(), const <Annotation>[],
           startLine: startLine, endLine: endLine)) {
         codeLine.lineAnnotation = codeSource;
         lines.add(codeLine);
       }
     }
     return lines;
   }
 
@@ skipping 30 matching lines @@
           startLine: interval.from, endLine: interval.to, uri: currentUri);
       if (codeSources != null) {
         CodeSource currentCodeSource;
         Interval currentLineInterval;
         for (CodeLine dartCodeLine in annotatedDartCodeLines) {
           if (currentCodeSource == null ||
               !currentLineInterval.contains(dartCodeLine.lineNo)) {
             currentCodeSource = null;
             for (CodeSource codeSource in codeSources) {
               Interval interval = new Interval(
-                  sourceFile.getLine(codeSource.begin),
-                  sourceFile.getLine(codeSource.end) + 1);
+                  sourceFile.getLocation(codeSource.begin).line - 1,
+                  sourceFile.getLocation(codeSource.end).line);
               if (interval.contains(dartCodeLine.lineNo)) {
                 currentCodeSource = codeSource;
                 currentLineInterval = interval;
                 break;
               }
             }
           }
           if (currentCodeSource != null) {
             dartCodeLine.lineAnnotation = currentCodeSource;
           }
@@ skipping 25 matching lines @@
       codeLineInterval.clear();
       codeLineInterval[codeLine] = interval;
     }
 
     for (CodeLine jsCodeLine in jsCodeLines) {
       for (Annotation annotation in jsCodeLine.annotations) {
         CodeLineAnnotation codeLineAnnotation = annotation.data;
 
         for (CodeLocation location in codeLineAnnotation.codeLocations) {
           SourceFile sourceFile = sourceFileManager.getSourceFile(location.uri);
-          int line = sourceFile.getLine(location.offset);
+          int line = sourceFile.getLocation(location.offset).line - 1;
           if (currentUri != location.uri) {
             restart(jsCodeLine, location, line);
           } else if (interval.inWindow(line, windowSize: 2)) {
             interval = interval.include(line);
             codeLineInterval[jsCodeLine] = interval;
           } else {
             restart(jsCodeLine, location, line);
           }
 
           annotations.add(new Annotation(codeLineAnnotation.annotationType,
@@ skipping 106 matching lines @@
         annotationType: AnnotationType.values[json['annotationType']],
         codeLocations: json['codeLocations']
             .map((j) => CodeLocation.fromJson(j, strategy))
             .toList(),
         codeSources:
             json['codeSources'].map((j) => CodeSource.fromJson(j)).toList(),
         stepInfo: json['stepInfo'],
         sourceMappingIndex: json['sourceMappingIndex']);
   }
 }