Switch transformers over to source_span

pkg/code_transformers/lib/assets.dart

 // 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.
 
 /// Common methods used by transfomers for dealing with asset IDs.
 library code_transformers.assets;
 
 import 'dart:math' show min, max;
 
 import 'package:barback/barback.dart';
 import 'package:path/path.dart' as path;
-import 'package:source_maps/span.dart' show Span;
+import 'package:source_span/source_span.dart';
 
 /// Create an [AssetId] for a [url] seen in the [source] asset.
 ///
 /// By default this is used to resolve relative urls that occur in HTML assets,
 /// including cross-package urls of the form "packages/foo/bar.html". Dart
 /// "package:" urls are not resolved unless [source] is Dart file (has a .dart
 /// extension).
 ///
 /// This function returns null if [url] can't be resolved. We log a warning
 /// message in [logger] if we know the reason why resolution failed. This
 /// happens, for example, when using incorrect paths to reach into another
 /// package, or when [errorsOnAbsolute] is true and the url seems to be
 /// absolute.
 // TODO(sigmund): delete once this is part of barback (dartbug.com/12610)
 AssetId uriToAssetId(AssetId source, String url, TransformLogger logger,
-    Span span, {bool errorOnAbsolute: true}) {
+    SourceSpan span, {bool errorOnAbsolute: true}) {
   if (url == null || url == '') return null;
   var uri = Uri.parse(url);
   var urlBuilder = path.url;
   if (uri.host != '' || uri.scheme != '' || urlBuilder.isAbsolute(url)) {
     if (source.extension == '.dart' && uri.scheme == 'package') {
       var index = uri.path.indexOf('/');
       if (index != -1) {
         return new AssetId(uri.path.substring(0, index),
             'lib${uri.path.substring(index)}');
       }
@@ skipping 48 matching lines @@
           'to: $fixedUrl', span: span);
       return null;
     }
   }
 
   // Otherwise, resolve as a path in the same package.
   return new AssetId(source.package, targetPath);
 }
 
 AssetId _extractOtherPackageId(int index, List segments,
-    TransformLogger logger, Span span) {
+    TransformLogger logger, SourceSpan span) {
   if (index >= segments.length) return null;
   var prefix = segments[index];
   if (prefix != 'packages' && prefix != 'assets') return null;
   var folder = prefix == 'packages' ? 'lib' : 'asset';
   if (segments.length < index + 3) {
     logger.warning("incomplete $prefix/ path. It should have at least 3 "
         "segments $prefix/name/path-from-name's-$folder-dir", span: span);
     return null;
   }
   return new AssetId(segments[index + 1],
       path.url.join(folder, path.url.joinAll(segments.sublist(index + 2))));
 }