First pass at asynchronous input loading in dart2js.

sdk/lib/_internal/compiler/implementation/apiimpl.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 leg_apiimpl;
 
 import 'dart:async';
 
 import '../compiler.dart' as api;
 import 'dart2jslib.dart' as leg;
@@ skipping 115 matching lines @@
 
   String lookupPatchPath(String dartLibraryName) {
     LibraryInfo info = LIBRARIES[dartLibraryName];
     if (info == null) return null;
     if (!info.isDart2jsLibrary) return null;
     String path = info.dart2jsPatchPath;
     if (path == null) return null;
     return "lib/$path";
   }
 
-  elements.LibraryElement scanBuiltinLibrary(String path) {
+  Future<elements.LibraryElement> scanBuiltinLibrary(String path) {
     Uri uri = libraryRoot.resolve(lookupLibraryPath(path));
     Uri canonicalUri = new Uri(scheme: "dart", path: path);
-    elements.LibraryElement library =
-        libraryLoader.loadLibrary(uri, null, canonicalUri);
-    return library;
+    return libraryLoader.loadLibrary(uri, null, canonicalUri);
   }
 
   void log(message) {
     handler(null, null, null, message, api.Diagnostic.VERBOSE_INFO);
   }
 
   /// See [leg.Compiler.translateResolvedUri].
   Uri translateResolvedUri(elements.LibraryElement importingLibrary,
                            Uri resolvedUri, tree.Node node) {
     if (resolvedUri.scheme == 'dart') {
       return translateDartUri(importingLibrary, resolvedUri, node);
     }
     return resolvedUri;
   }
 
   /**
    * Reads the script designated by [readableUri].
    */
-  leg.Script readScript(Uri readableUri, [tree.Node node]) {
+  Future<leg.Script> readScript(Uri readableUri,
+                                [elements.Element element, tree.Node node]) {
     if (!readableUri.isAbsolute) {
       internalError('Relative uri $readableUri provided to readScript(Uri)',
                     node: node);
     }
-    return fileReadingTask.measure(() {
-      Uri resourceUri = translateUri(readableUri, node);
-      String text = "";
-      try {
-        // TODO(ahe): We expect the future to be complete and call value
-        // directly. In effect, we don't support truly asynchronous API.
-        text = deprecatedFutureValue(provider(resourceUri));
-      } catch (exception) {
+
+    // TODO(johnniwinther): Add [:report(..., {Element element}):] to
+    // report methods in Compiler.
+    void reportReadError(String exception) {
+      withCurrentElement(element, () {
         reportError(node,
                     leg.MessageKind.READ_SCRIPT_ERROR,
                     {'uri': readableUri, 'exception': exception});
-        return null;
-      }
+      });
+    }
+
+    Uri resourceUri = translateUri(readableUri, node);
+    // TODO(johnniwinther): Wrap the result from [provider] in a specialized
+    // [Future] to ensure that we never execute an asynchronous action without setting
+    // up the current element of the compiler.
+    return new Future.sync(() => provider(resourceUri)).then((String text) {
       SourceFile sourceFile = new SourceFile(resourceUri.toString(), text);
       // We use [readableUri] as the URI for the script since need to preserve
       // the scheme in the script because [Script.uri] is used for resolving
       // relative URIs mentioned in the script. See the comment on
       // [LibraryLoader] for more details.
       return new leg.Script(readableUri, sourceFile);
+    }).catchError((error) {
+      reportReadError(error);
+      return null;
     });
   }
 
   /**
    * Translates a readable URI into a resource URI.
    *
    * See [LibraryLoader] for terminology on URIs.
    */
   Uri translateUri(Uri readableUri, tree.Node node) {
     switch (readableUri.scheme) {
@@ skipping 53 matching lines @@
   }
 
   Uri translatePackageUri(Uri uri, tree.Node node) {
     if (packageRoot == null) {
       reportFatalError(
           node, leg.MessageKind.PACKAGE_ROOT_NOT_SET, {'uri': uri});
     }
     return packageRoot.resolve(uri.path);
   }
 
-  bool run(Uri uri) {
+  Future<bool> run(Uri uri) {
     log('Allowed library categories: $allowedLibraryCategories');
-    bool success = super.run(uri);
-    int cumulated = 0;
-    for (final task in tasks) {
-      cumulated += task.timing;
-      log('${task.name} took ${task.timing}msec');
-    }
-    int total = totalCompileTime.elapsedMilliseconds;
-    log('Total compile-time ${total}msec;'
-        ' unaccounted ${total - cumulated}msec');
-    return success;
+    return super.run(uri).then((bool success) {
+      int cumulated = 0;
+      for (final task in tasks) {
+        cumulated += task.timing;
+        log('${task.name} took ${task.timing}msec');
+      }
+      int total = totalCompileTime.elapsedMilliseconds;
+      log('Total compile-time ${total}msec;'
+          ' unaccounted ${total - cumulated}msec');
+      return success;
+    });
   }
 
   void reportDiagnostic(leg.SourceSpan span, String message,
                         api.Diagnostic kind) {
     if (identical(kind, api.Diagnostic.ERROR)
         || identical(kind, api.Diagnostic.CRASH)) {
       compilationFailed = true;
     }
     // [:span.uri:] might be [:null:] in case of a [Script] with no [uri]. For
     // instance in the [Types] constructor in typechecker.dart.
     if (span == null || span.uri == null) {
       handler(null, null, null, message, kind);
     } else {
       handler(translateUri(span.uri, null), span.begin, span.end,
               message, kind);
     }
   }
 
   bool get isMockCompilation {
     return mockableLibraryUsed
       && (options.indexOf('--allow-mock-compilation') != -1);
   }
 }