Extract out a source_span package from source_maps.

pkg/source_span/lib/src/source_span_mixin.dart

Index: pkg/source_span/lib/src/source_span_mixin.dart
diff --git a/pkg/source_span/lib/src/source_span_mixin.dart b/pkg/source_span/lib/src/source_span_mixin.dart
new file mode 100644
index 0000000000000000000000000000000000000000..c4d28663bed3426e51aa1c481652ddc16aafbd39
--- /dev/null
+++ b/pkg/source_span/lib/src/source_span_mixin.dart
@@ -0,0 +1,74 @@
+// 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.source_span_mixin;
+
+import 'package:path/path.dart' as p;
+
+import 'colors.dart' as colors;
+import 'source_span.dart';
+import 'utils.dart';
+
+/// A mixin for easily implementing [SourceSpan].
+///
+/// This implements the [SourceSpan] methods in terms of [start], [end], and
+/// [text]. This assumes that [start] and [end] have the same source URL, that
+/// [start] comes before [end], and that [text] has a number of characters equal
+/// to the distance between [start] and [end].
+abstract class SourceSpanMixin implements SourceSpan {
+  Uri get sourceUrl => start.sourceUrl;
+  int get length => end.offset - start.offset;
+
+  int compareTo(SourceSpan other) {
+    int d = start.compareTo(other.start);
+    return d == 0 ? end.compareTo(other.end) : d;
+  }
+
+  SourceSpan union(SourceSpan other) {
+    if (sourceUrl != other.sourceUrl) {
+      throw new ArgumentError("Source URLs \"${sourceUrl}\" and "
+          " \"${other.sourceUrl}\" don't match.");
+    }
+
+    var start = min(this.start, other.start);
+    var end = max(this.end, other.end);
+    var beginSpan = start == this.start ? this : other;
+    var endSpan = end == this.end ? this : other;
+
+    if (beginSpan.end.compareTo(endSpan.start) < 0) {
+      throw new ArgumentError("Spans $this and $other are disjoint.");
+    }
+
+    var text = beginSpan.text +
+        endSpan.text.substring(beginSpan.end.distance(endSpan.start));

[Siggi Cherem (dart-lang), 2014/07/16 21:26:10]

for disjoint unions, we could use a text with ' ... ' in the middle or null
text, for union in File spans, we can use the original source file to figure out
the text.

[nweiz, 2014/07/17 20:22:08]

I don't like the idea of making [text] not match [length], or even of having it
not be actual text from the document. Users should be confident that the spans
returned by these methods are just as accurate as the spans they put in.

For an alternate possibility, though, see FileSpan.expand.

+    return new SourceSpan(start, end, text);
+  }
+
+  String message(String message, {color}) {
+    if (color == true) color = colors.RED;
+    if (color == false) color = null;
+
+    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');
+    if (length == 0) return buffer.toString();
+
+    buffer.write("\n");
+    var textLine = text.split("\n").first;

[Siggi Cherem (dart-lang), 2014/07/16 21:26:10]

not sure I follow why just the first line?

[nweiz, 2014/07/17 20:22:08]

To match the old behavior. I'd like to look into making this work better for
multiline spans, but that's something for another CL.

+    if (color != null) buffer.write(color);
+    buffer.write(textLine);
+    buffer.write("\n");
+    buffer.write('^' * textLine.length);
+    if (color != null) buffer.write(colors.NONE);
+    return buffer.toString();
+  }
+
+  bool operator ==(SourceSpan other) =>
+      start == other.start && end == other.end;
+
+  int get hashCode => start.hashCode + (31 * end.hashCode);
+
+  String toString() => '<$runtimeType: from $start to $end "$text">';
+}