Introduce span with line context

lib/src/file.dart

Index: lib/src/file.dart
diff --git a/lib/src/file.dart b/lib/src/file.dart
index ed5f6a8371226ed65065789a6ec8ee043701426f..953a6afdbfce86b2aaf23eb2f21052a801f71280 100644
--- a/lib/src/file.dart
+++ b/lib/src/file.dart
@@ -12,6 +12,7 @@ import 'package:path/path.dart' as p;
 import 'colors.dart' as colors;
 import 'location.dart';
 import 'span.dart';
+import 'span_context.dart';
 import 'span_mixin.dart';
 import 'utils.dart';
 
@@ -183,7 +184,7 @@ class FileLocation extends SourceLocation {
 /// [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 SourceSpanContext {
   /// The [file] that [this] belongs to.
   final SourceFile file;
 
@@ -262,40 +263,9 @@ class FileSpan extends SourceSpanMixin {
     return new FileSpan._(file, start, end);
   }
 
-  String message(String message, {color}) {

[Siggi Cherem (dart-lang), 2015/03/21 00:19:59]

the old logic basically is now shared with the default `message` implementation

-    if (color == true) color = colors.RED;
-    if (color == false) color = null;
-
+  String get contextLine {

[nweiz, 2015/03/24 23:01:17]

Nit: put getters above the constructor.

[Siggi Cherem (dart-lang), 2015/03/25 00:33:25]

Done.

     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),
+    return 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();
   }
 }