Recover from read errors.

dart/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 470 matching lines @@
     if (readableUri == null) return new Future.value();
     return compiler.withCurrentElement(library, () {
       return compiler.readScript(part, readableUri).
           then((Script sourceScript) {
             if (sourceScript == null) return;
 
             CompilationUnitElement unit =
                 new CompilationUnitElementX(sourceScript, library);
             compiler.withCurrentElement(unit, () {
               compiler.scanner.scan(unit);
-              if (unit.partTag == null) {
+              if (unit.partTag == null && !sourceScript.isSynthesized) {
                 compiler.reportError(unit, MessageKind.MISSING_PART_OF_TAG);
               }
             });
           });
     });
   }
 
   /**
    * Handle an import/export tag by loading the referenced library and
    * registering its dependency in [handler] for the computation of the import/
@@ skipping 16 matching lines @@
   /**
    * Create (or reuse) a library element for the library specified by the
    * [resolvedUri].
    *
    * If a new library is created, the [handler] is notified.
    */
   Future<LibraryElement> createLibrary(LibraryDependencyHandler handler,
                                        LibraryElement importingLibrary,
                                        Uri resolvedUri,
                                        [Node node]) {
-    // TODO(johnniwinther): Create erroneous library elements for missing
-    // libraries.
     Uri readableUri =
         compiler.translateResolvedUri(importingLibrary, resolvedUri, node);
-    if (readableUri == null) return new Future.value();
     LibraryElement library = libraryCanonicalUriMap[resolvedUri];
     if (library != null) {
       return new Future.value(library);
     }
+    var readScript = compiler.readScript;
+    if (readableUri == null) {
+      readableUri = resolvedUri;
+      readScript = compiler.synthesizeScript;
+    }
     return compiler.withCurrentElement(importingLibrary, () {
-      return compiler.readScript(node, readableUri).then((Script script) {
+      return readScript(node, readableUri).then((Script script) {
         if (script == null) return null;
         LibraryElement element =
             createLibrarySync(handler, script, resolvedUri);
         return processLibraryTags(handler, element).then((_) {
           compiler.withCurrentElement(element, () {
             handler.registerLibraryExports(element);
           });
           return element;
         });
       });
@@ skipping 635 matching lines @@
         }
         suffixes.add(const Link<Uri>().prepend(canonicalUri));
       }
       suffixChainMap[library] = suffixes;
       return;
     }
 
     computeSuffixes(rootLibrary, const Link<Uri>());
   }
 }