Introduce span with line context

lib/src/file.dart

 // Copyright (c) 2014, 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 source_span.file;
 
 import 'dart:math' as math;
 import 'dart:typed_data';
 
 import 'package:path/path.dart' as p;
 
 import 'colors.dart' as colors;
 import 'location.dart';
 import 'span.dart';
 import 'span_mixin.dart';
+import 'span_with_context.dart';
 import 'utils.dart';
 
 // Constants to determine end-of-lines.
 const int _LF = 10;
 const int _CR = 13;
 
 /// A class representing a source file.
 ///
 /// This doesn't necessarily have to correspond to a file on disk, just a chunk
 /// of text usually with a URL associated with it.
@@ skipping 150 matching lines @@
 }
 
 /// A [SourceSpan] within a [SourceFile].
 ///
 /// Unlike the base [SourceSpan], [FileSpan] lazily computes its line and column
 /// values based on its offset and the contents of [file]. [FileSpan.message] is
 /// also able to provide more context then [SourceSpan.message], and
 /// [FileSpan.union] will return a [FileSpan] if possible.
 ///
 /// A [FileSpan] can be created using [SourceFile.span].
-class FileSpan extends SourceSpanMixin {
+class FileSpan extends SourceSpanMixin implements SourceSpanWithContext {
   /// The [file] that [this] belongs to.
   final SourceFile file;
 
   /// The offset of the beginning of the span.
   ///
   /// [start] is lazily generated from this to avoid allocating unnecessary
   /// objects.
   final int _start;
 
   /// The offset of the end of the span.
   ///
   /// [end] is lazily generated from this to avoid allocating unnecessary
   /// objects.
   final int _end;
 
   Uri get sourceUrl => file.url;
   int get length => _end - _start;
   FileLocation get start => new FileLocation._(file, _start);
   FileLocation get end => new FileLocation._(file, _end);
   String get text => file.getText(_start, _end);
 
+  String get context {
+    var line = start.line;
+    return file.getText(file.getOffset(line),
+        line == file.lines - 1 ? null : file.getOffset(line + 1));
+  }
+
   FileSpan._(this.file, this._start, this._end) {
     if (_end < _start) {
       throw new ArgumentError('End $_end must come after start $_start.');
     } else if (_end > file.length) {
       throw new RangeError("End $_end must not be greater than the number "
           "of characters in the file, ${file.length}.");
     } else if (_start < 0) {
       throw new RangeError("Start may not be negative, was $_start.");
     }
   }
@@ skipping 36 matching lines @@
   FileSpan expand(FileSpan other) {
     if (sourceUrl != other.sourceUrl) {
       throw new ArgumentError("Source URLs \"${sourceUrl}\" and "
           " \"${other.sourceUrl}\" don't match.");
     }
 
     var start = math.min(this._start, other._start);
     var end = math.max(this._end, other._end);
     return new FileSpan._(file, start, end);
   }
-
-  String message(String message, {color}) {
-    if (color == true) color = colors.RED;
-    if (color == false) color = null;
-
-    var line = start.line;
-    var column = start.column;
-
-    var buffer = new StringBuffer();
-    buffer.write('line ${start.line + 1}, column ${start.column + 1}');
-    if (sourceUrl != null) buffer.write(' of ${p.prettyUri(sourceUrl)}');
-    buffer.write(': $message\n');
-
-    var textLine = file.getText(file.getOffset(line),
-        line == file.lines - 1 ? null : file.getOffset(line + 1));
-
-    column = math.min(column, textLine.length - 1);
-    var toColumn =
-        math.min(column + end.offset - start.offset, textLine.length);
-
-    if (color != null) {
-      buffer.write(textLine.substring(0, column));
-      buffer.write(color);
-      buffer.write(textLine.substring(column, toColumn));
-      buffer.write(colors.NONE);
-      buffer.write(textLine.substring(toColumn));
-    } else {
-      buffer.write(textLine);
-    }
-    if (!textLine.endsWith('\n')) buffer.write('\n');
-
-    buffer.write(' ' * column);
-    if (color != null) buffer.write(color);
-    buffer.write('^' * math.max(toColumn - column, 1));
-    if (color != null) buffer.write(colors.NONE);
-    return buffer.toString();
-  }
 }