Report malformed URIs in library dependencies

pkg/compiler/lib/src/library_loader.dart

 // Copyright (c) 2012, 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 dart2js.library_loader;
 
 import 'dart:async';
 
 import 'dart2jslib.dart' show
     Compiler,
@@ skipping 487 matching lines @@
 
   /**
    * Handle an import/export tag by loading the referenced library and
    * registering its dependency in [handler] for the computation of the import/
    * export scope.
    */
   Future registerLibraryFromTag(LibraryDependencyHandler handler,
                                 LibraryElement library,
                                 LibraryDependency tag) {
     Uri base = library.canonicalUri;
-    Uri resolvedUri = base.resolve(tag.uri.dartString.slowToString());
+    String tagUriString = tag.uri.dartString.slowToString();
+    Uri resolvedUri;
+    try {
+      resolvedUri = base.resolve(tagUriString);
+    } on FormatException {
+      compiler.reportError(
+          tag, MessageKind.INVALID_URI, {'uri': tagUriString});
+      return new Future.value();

[floitsch, 2015/05/06 21:19:00]

This return feels fishy.
Is the convention that this function returns a Future<null> if it couldn't load
the library? If yes, this should be part of the comment.

My guess is, that reportError was fatal and something changed.
Alternative guess is that the test's error-collector is not fatal (whereas the
dart2js one is).

In either case it's worth adding more documentation:
- add it as comment in the dartdoc.
- add a comment here: // compiler.reportError might not abort computation.

+    }
     return createLibrary(handler, library, resolvedUri, tag.uri)
         .then((LibraryElement loadedLibrary) {
           if (loadedLibrary == null) return;
           compiler.withCurrentElement(library, () {
             handler.registerDependency(library, tag, loadedLibrary);
           });
         });
   }
 
   /**
@@ skipping 667 matching lines @@
         }
         suffixes.add(const Link<Uri>().prepend(canonicalUri));
       }
       suffixChainMap[library] = suffixes;
       return;
     }
 
     computeSuffixes(rootLibrary, const Link<Uri>());
   }
 }