Introduce span with line context

lib/src/span.dart

Index: lib/src/span.dart
diff --git a/lib/src/span.dart b/lib/src/span.dart
index 9f150482c6da354adbbad9753a12a306b4bf432c..bb66d169f8eb95d56c98c0fe6de0b43137a992b8 100644
--- a/lib/src/span.dart
+++ b/lib/src/span.dart
@@ -5,6 +5,7 @@
 library source_span.span;
 
 import 'location.dart';
+import 'span_context.dart';
 import 'span_mixin.dart';
 
 /// A class that describes a segment of source text.
@@ -76,3 +77,26 @@ class SourceSpanBase extends SourceSpanMixin {
     }
   }
 }
+
+/// A class that describes a segment of source text.

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

Update this doc comment.

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

Done.

+class SourceSpanWithContext extends SourceSpanBase
+    implements SourceSpanContext {
+  /// Line containing the source-span

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

"The text of the line containing this span.

If the span covers multiple lines, this should only contain the first."

I've considered for a while having multi-line spans produce multi-line messages,
so maybe this variable's name should be updated to be forwards-compatible with
those semantics. Maybe just [context]?

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

Sounds good. Done

+  final String contextLine;
+
+  /// Creates a new span from [start] to [end] (exclusive) containing [text], in
+  /// the context of [contextLine].
+  ///
+  /// [start] and [end] must have the same source URL and [start] must come
+  /// before [end]. [text] must have a number of characters equal to the
+  /// distance between [start] and [end]. [contextLine] must contain [text], and
+  /// [text] should start at `start.column`.
+  SourceSpanWithContext(SourceLocation start, SourceLocation end, String text,
+      this.contextLine) : super(start, end, text) {

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

Nit: put the super call on its own line.

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

Done. This made me realized I was not running the formatter, so I went ahead and
ran it on the entire package

[nweiz, 2015/03/25 01:10:39]

I actually prefer to have format-everything CLs separate from functional CLs,
since they create a lot of churn. Also, it looks like a lot of the formatting
changes for this package are the same or worse than the original (especially in
the tests), so I'd rather not include them.

[Siggi Cherem (dart-lang), 2015/03/26 21:07:29]

OK reverted all other formatter changes.

In dev_compiler we are running the formatter on every CL so we don't think about
it anymroe

+    var index = contextLine.indexOf(text);
+    if (index != start.column) {
+      throw new ArgumentError('The context line "$contextLine" must '
+          'contain "$text" starting at column ${start.column + 1}.');

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

I'd throw separate errors for [contextLine] not containing [text] and for the
column being wrong, so that it's easier for users to figure out what's going
wrong.

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

Done.

+    }
+  }
+}