Fix source spans hashcode implementation

pkg/source_maps/lib/span.dart

Index: pkg/source_maps/lib/span.dart
diff --git a/pkg/source_maps/lib/span.dart b/pkg/source_maps/lib/span.dart
index 1d2152da70c4e59c7ff0a1b58d9dcac0f8c28af6..e5057fcebd717785f9c1330b877d9045c1250d61 100644
--- a/pkg/source_maps/lib/span.dart
+++ b/pkg/source_maps/lib/span.dart
@@ -69,7 +69,7 @@ abstract class Span implements Comparable {
   bool operator ==(Span other) =>
     sourceUrl == other.sourceUrl && start == other.start && end == other.end;
 
-  int get hashCode => sourceUrl.hashCode + start + (31 * (end - start));
+  int get hashCode => sourceUrl.hashCode + start.offset + (31 * length);

[justinfagnani, 2013/07/26 00:44:22]

length includes information from start.offset already, why not just end.offset?

[Siggi Cherem (dart-lang), 2013/07/26 00:50:12]

I could argue the opposite: end.offset is always > start, so only length is a
relevant piece =)

I think it's ok either way, but I'm afraid of offsets*31 being too large, so
just encoding the length might be better. 

 
   String toString() => '<$runtimeType: $start $end $formatLocation $text>';
 }
@@ -99,6 +99,11 @@ abstract class Location implements Comparable {
     return offset - other.offset;
   }
 
+  bool operator ==(Location other) =>
+      sourceUrl == other.sourceUrl && offset == other.offset;
+
+  int get hashCode => sourceUrl.hashCode + offset;
+
   String toString() => '(Location $offset)';
   String get formatString => '$sourceUrl:${line + 1}:${column + 1}';
 }