Fix tab highlighting. (dart-lang/source_span#14)

diff --git a/pkgs/source_span/CHANGELOG.md b/pkgs/source_span/CHANGELOG.md
index afcc493..0176b9f 100644
--- a/pkgs/source_span/CHANGELOG.md
+++ b/pkgs/source_span/CHANGELOG.md

@@ -1,3 +1,8 @@
+# 1.3.1
+
+* Properly highlight spans for lines that include tabs with
+  `SourceSpan.highlight()` and `SourceSpan.message()`.
+
 # 1.3.0
 
 * Add `SourceSpan.highlight()`, which returns just the highlighted text that

diff --git a/pkgs/source_span/lib/src/span_mixin.dart b/pkgs/source_span/lib/src/span_mixin.dart
index 8d84cea..06e2024 100644
--- a/pkgs/source_span/lib/src/span_mixin.dart
+++ b/pkgs/source_span/lib/src/span_mixin.dart

@@ -3,6 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:math' as math;
+
+import 'package:charcode/charcode.dart';
 import 'package:path/path.dart' as p;
 
 import 'colors.dart' as colors;
@@ -96,7 +98,15 @@
       buffer.write(textLine);
     }
     if (!textLine.endsWith('\n')) buffer.write('\n');
-    buffer.write(' ' * column);
+
+    for (var i = 0; i < column; i++) {
+      if (textLine.codeUnitAt(i) == $tab) {
+        buffer.writeCharCode($tab);
+      } else {
+        buffer.writeCharCode($space);
+      }
+    }
+
     if (color != null) buffer.write(color);
     buffer.write('^' * math.max(toColumn - column, 1));
     if (color != null) buffer.write(colors.NONE);

diff --git a/pkgs/source_span/pubspec.yaml b/pkgs/source_span/pubspec.yaml
index 8fa8711..d340d85 100644
--- a/pkgs/source_span/pubspec.yaml
+++ b/pkgs/source_span/pubspec.yaml

@@ -1,9 +1,10 @@
 name: source_span
-version: 1.3.0
+version: 1.3.1
 author: Dart Team <misc@dartlang.org>
 description: A library for identifying source spans and locations.
 homepage: https://github.com/dart-lang/source_span
 dependencies:
+  charcode: '^1.0.0'
   path: '>=1.2.0 <2.0.0'
 environment:
   sdk: '>=0.8.10+6 <2.0.0'

diff --git a/pkgs/source_span/test/highlight_test.dart b/pkgs/source_span/test/highlight_test.dart
index 32b09ff..74faed5 100644
--- a/pkgs/source_span/test/highlight_test.dart
+++ b/pkgs/source_span/test/highlight_test.dart

@@ -75,6 +75,13 @@
 ^^^^^^^"""));
   });
 
+  test("emits tabs for tabs", () {
+    expect(new SourceFile(" \t \t\tfoo bar").span(5, 8).highlight(),
+        equals("""
+ \t \t\tfoo bar
+ \t \t\t^^^"""));
+  });
+
   test("supports lines of preceding context", () {
     var span = new SourceSpanWithContext(
         new SourceLocation(5, line: 3, column: 5, sourceUrl: "foo.dart"),