Rev package version as the extended source map format is a new feature.

lib/parser.dart

 // Copyright (c) 2013, 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.
 
 /// Contains the top-level function to parse source maps version 3.
 library source_maps.parser;
 
 import 'dart:collection';
 import 'dart:convert';
 
@@ skipping 187 matching lines @@
       buff.write(map.toString());
     }
     return buff.toString();
   }
 
   SourceMapSpan spanFor(int line, int column,
       {Map<String, SourceFile> files, String uri}) {
     if (uri == null) {
       throw new ArgumentError.notNull('uri');
     }
-    if (_mappings.containsKey(uri)) {
-      return _mappings[uri].spanFor(line, column, files: files, uri: uri);
-    }
-    // Fall back to looking up the source map on just the basename.
-    var name = path.basename(uri.toString());
-    if (_mappings.containsKey(name)) {
-      return _mappings[name].spanFor(line, column, files: files, uri: name);
+
+    // Fall back to looking up uri suffixes of decreasing length if the full

[Siggi Cherem (dart-lang), 2016/12/14 15:46:10]

Let's keep the first `if` from before (where you check containsKey(uri))

I know it's handled with `i=0`, but it is less work (no split/join) and it will
make it more clear that the suffix mechanism is a fallback.

[Jacob, 2016/12/14 18:49:42]

Changed the wording of the comment from fall back to 
"Find the longest suffix of the uri that matches the sourcemap"
That should make the existing code clearer.
In practice for typical web server uses of this code, the full uri
will never actually match the _mappings so there is no point 
in optimizing that case.

+    // uri does not match a source map.
+    var parts = path.split(uri);

[Siggi Cherem (dart-lang), 2016/12/14 15:46:10]

do we expect uri to contain any scheme? (do we need to first extract the path
out of the uri?)

[Jacob, 2016/12/14 18:49:42]

Good point.
path.split doesn't handle package: the way I need it to be handled.
Switched for manually finding split points instead of using path.split and
path.join
Added a few other tests to check for windows paths as well as package: paths.

+    for (var i = 0; i < parts.length; ++i) {
+      var candidate = path.joinAll(parts.skip(i));
+      if (_mappings.containsKey(candidate)) {
+        return _mappings[candidate]
+            .spanFor(line, column, files: files, uri: candidate);
+      }
     }
 
     // Note: when there is no source map for an uri, this behaves like an
     // identity function, returning the requested location as the result.
 
     // Create a mock offset for the output location. We compute it in terms
     // of the input line and column to minimize the chances that two different
     // line and column locations are mapped to the same offset.
     var offset = line * 1000000 + column;
     var location = new SourceLocation(offset,
@@ skipping 386 matching lines @@
   static const _TokenKind EOF = const _TokenKind(isEof: true);
   static const _TokenKind VALUE = const _TokenKind();
   final bool isNewLine;
   final bool isNewSegment;
   final bool isEof;
   bool get isValue => !isNewLine && !isNewSegment && !isEof;
 
   const _TokenKind(
       {this.isNewLine: false, this.isNewSegment: false, this.isEof: false});
 }