Added support for exports and re-exports.

lib/compiler/implementation/library_loader.dart

Index: lib/compiler/implementation/library_loader.dart
diff --git a/lib/compiler/implementation/library_loader.dart b/lib/compiler/implementation/library_loader.dart
index b91001b4a45efd9e48cadaf0fb0779d08cdfa213..c1011760eeba1efff8c72b5510934bc288db8bcb 100644
--- a/lib/compiler/implementation/library_loader.dart
+++ b/lib/compiler/implementation/library_loader.dart
@@ -2,27 +2,74 @@
 // 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.
 
-class ScannerTask extends CompilerTask {
-  ScannerTask(Compiler compiler) : super(compiler);
-  String get name => 'Scanner';
+/**
+ * [CompilerTask] for loading libraries and setting up the import/export scopes.
+ */
+abstract class LibraryLoader extends CompilerTask {
+  LibraryLoader(Compiler compiler) : super(compiler);
+
+  /**
+   * Loads the library located at [uri] and returns its [LibraryElement].
+   *
+   * If the library is not already loaded, the method creates the
+   * [LibraryElement] for the library and computes the import/export scope,
+   * loading and computing the import/export scopes of all required libraries in
+   * the process. The method handles cyclic dependency between libraries.
+   *
+   * This is the main entry point for [LibraryLoader].
+   */
+  abstract LibraryElement loadLibrary(Uri uri, Node node, Uri canonicalUri);
+
+  // TODO(johnniwinther): Remove this when patches don't need special parsing.
+  abstract void registerLibraryFromTag(LibraryDependencyHandler handler,
+                                       LibraryElement library,
+                                       LibraryDependency tag);
+
+  /**
+   * Adds the elements in the export scope of [importedLibrary] to the import
+   * scope of [importingLibrary].
+   */
+  // TODO(johnniwinther): Move handling of 'js_helper' to the library loader
+  // to remove this method from the [LibraryLoader] interface.
+  abstract void importLibrary(LibraryElement importingLibrary,
+                              LibraryElement importedLibrary,
+                              Import tag);
+}
+
+/**
+ * Implementation class for [LibraryLoader]. The distinction between
+ * [LibraryLoader] and [LibraryLoaderTask] is made to hide internal members from
+ * the [LibraryLoader] interface.
+ */
+class LibraryLoaderTask extends LibraryLoader {
+  LibraryLoaderTask(Compiler compiler) : super(compiler);
+  String get name => 'LibraryLoader';
 
   final Map<String, LibraryElement> libraryNames =
       new Map<String, LibraryElement>();
 
-  void scanLibrary(LibraryElement library) {
-    var compilationUnit = library.entryCompilationUnit;
-    compiler.log("scanning library ${compilationUnit.script.name}");
-    scan(compilationUnit);
-    processLibraryTags(library);
-  }
+  LibraryDependencyHandler currentHandler;
 
-  void scan(CompilationUnitElement compilationUnit) {
-    measure(() {
-      scanElements(compilationUnit);
+  LibraryElement loadLibrary(Uri uri, Node node, Uri canonicalUri) {
+    return measure(() {
+      assert(currentHandler == null);
+      currentHandler = new LibraryDependencyHandler(compiler);
+      LibraryElement library =
+          createLibrary(currentHandler, uri, node, canonicalUri);
+      currentHandler.computeExports();
+      currentHandler = null;
+      return library;
     });
   }
 
-  void processLibraryTags(LibraryElement library) {
+  /**
+   * Processes the library tags in [library].
+   *
+   * The imported/exported libraries are loaded and processed recursively but
+   * the import/export scopes are not set up.
+   */
+  void processLibraryTags(LibraryDependencyHandler handler,
+                          LibraryElement library) {
     int tagState = TagState.NO_TAG_SEEN;
 
     /**
@@ -38,19 +85,22 @@ class ScannerTask extends CompilerTask {
       return TagState.NEXT[value];
     }
 
-    LinkBuilder<Import> imports = new LinkBuilder<Import>();
+    bool importsDartCore = false;
+    var libraryDependencies = new LinkBuilder<LibraryDependency>();
     Uri base = library.entryCompilationUnit.script.uri;
     for (LibraryTag tag in library.tags.reverse()) {
       if (tag.isImport) {
-        tagState = checkTag(TagState.IMPORT, tag);
+        tagState = checkTag(TagState.IMPORT_OR_EXPORT, tag);
         if (tag.combinators != null) {
           compiler.unimplemented('combinators', node: tag.combinators);
         }
-        // It is not safe to import other libraries at this point as
-        // another library could then observe the current library
-        // before it fully declares all the members that are sourced
-        // in.
-        imports.addLast(tag);
+        if (tag.uri.dartString.slowToString() == 'dart:core') {
+          importsDartCore = true;
+        }
+        libraryDependencies.addLast(tag);
+      } else if (tag.isExport) {
+        tagState = checkTag(TagState.IMPORT_OR_EXPORT, tag);
+        libraryDependencies.addLast(tag);
       } else if (tag.isLibraryName) {
         tagState = checkTag(TagState.LIBRARY, tag);
         if (library.libraryTag !== null) {
@@ -63,7 +113,7 @@ class ScannerTask extends CompilerTask {
         StringNode uri = tag.uri;
         Uri resolved = base.resolve(uri.dartString.slowToString());
         tagState = checkTag(TagState.SOURCE, tag);
-        loadPart(tag, resolved, library);
+        scanPart(tag, resolved, library);
       } else {
         compiler.internalError("Unhandled library tag.", node: tag);
       }
@@ -71,23 +121,21 @@ class ScannerTask extends CompilerTask {
 
     // Apply patch, if any.
     if (library.uri.scheme == 'dart') {
-      compiler.patchDartLibrary(library, library.uri.path);
+      patchDartLibrary(handler, library, library.uri.path);
     }
 
-    // Now that we have processed all the source tags, it is safe to
-    // start loading other libraries.
-
-    if (library.uri.scheme != 'dart' || library.uri.path != 'core') {
-      compiler.importCoreLibrary(library);
+    // Import dart:core if not already imported.
+    if (!importsDartCore && !isDartCore(library.uri)) {
+      handler.registerDependency(library, null, loadCoreLibrary(handler));
     }
 
-    for (Import tag in imports.toLink()) {
-      importLibraryFromTag(tag, library.entryCompilationUnit);
+    for (LibraryDependency tag in libraryDependencies.toLink()) {
+      registerLibraryFromTag(handler, library, tag);
     }
   }
 
   void checkDuplicatedLibraryName(LibraryElement library) {
-    LibraryTag tag = library.libraryTag;
+    LibraryName tag = library.libraryTag;
     if (tag != null) {
       String name = library.getLibraryOrScriptName();
       LibraryElement existing =
@@ -97,56 +145,84 @@ class ScannerTask extends CompilerTask {
         compiler.reportMessage(
             compiler.spanFromNode(tag.name, uri),
             MessageKind.DUPLICATED_LIBRARY_NAME.error([name]),
-            api_s.Diagnostic.WARNING);
+            api.Diagnostic.WARNING);
         Uri existingUri = existing.entryCompilationUnit.script.uri;
         compiler.reportMessage(
             compiler.spanFromNode(existing.libraryTag.name, existingUri),
             MessageKind.DUPLICATED_LIBRARY_NAME.error([name]),
-            api_s.Diagnostic.WARNING);
+            api.Diagnostic.WARNING);
       }
     }
   }
 
+  bool isDartCore(Uri uri) => uri.scheme == "dart" && uri.path == "core";
+
+  /**
+   * Lazily loads and returns the [LibraryElement] for the dart:core library.
+   */
+  LibraryElement loadCoreLibrary(LibraryDependencyHandler handler) {
+    if (compiler.coreLibrary === null) {
+      Uri coreUri = new Uri.fromComponents(scheme: 'dart', path: 'core');
+      compiler.coreLibrary = createLibrary(handler, coreUri, null, coreUri);
+    }
+    return compiler.coreLibrary;
+  }
+
+  void patchDartLibrary(LibraryDependencyHandler handler,
+                        LibraryElement library, String dartLibraryPath) {
+    if (library.isPatched) return;
+    Uri patchUri = compiler.resolvePatchUri(dartLibraryPath);
+    if (patchUri !== null) {
+      compiler.patchParser.patchLibrary(handler, patchUri, library);
+    }
+  }
+
   /**
    * Handle a part tag in the scope of [library]. The [path] given is used as
-   * is, any resolution should be done beforehand.
+   * is, any URI resolution should be done beforehand.
    */
-  void loadPart(Part part, Uri path, LibraryElement library) {
-    Script sourceScript = compiler.readScript(path, part.uri);
+  void scanPart(Part part, Uri path, LibraryElement library) {
+    if (!path.isAbsolute()) throw new ArgumentError(path);
+    Script sourceScript = compiler.readScript(path, part);
     CompilationUnitElement unit =
         new CompilationUnitElement(sourceScript, library);
     compiler.withCurrentElement(unit, () => compiler.scanner.scan(unit));
   }
 
   /**
-   * Handle an import script tag by importing the referenced library into the
-   * current library.
-   * Returns the resolved library [Uri].
+   * Handle an import/export tag by loading the referenced library and
+   * registering its dependency in [handler] for the computation of the import/
+   * export scope.
    */
-  Uri importLibraryFromTag(Import tag,
-                           CompilationUnitElement compilationUnit) {
-    Uri base = compilationUnit.script.uri;
+  void registerLibraryFromTag(LibraryDependencyHandler handler,
+                              LibraryElement library,
+                              LibraryDependency tag) {
+    Uri base = library.entryCompilationUnit.script.uri;
     Uri resolved = base.resolve(tag.uri.dartString.slowToString());
-    LibraryElement importedLibrary = loadLibrary(resolved, tag.uri, resolved);
-    importLibrary(compilationUnit.getLibrary(),
-                  importedLibrary,
-                  tag,
-                  compilationUnit);
-    return resolved;
-  }
+    LibraryElement loadedLibrary =
+        createLibrary(handler, resolved, tag.uri, resolved);
+    handler.registerDependency(library, tag, loadedLibrary);
 
-  void scanElements(CompilationUnitElement compilationUnit) {
-    Script script = compilationUnit.script;
-    Token tokens = new StringScanner(script.text).tokenize();
-    compiler.dietParser.dietParse(compilationUnit, tokens);
+    if (!loadedLibrary.hasLibraryName()) {
+      compiler.withCurrentElement(library, () {
+        compiler.reportError(tag === null ? null : tag.uri,
+            'no library name found in ${loadedLibrary.uri}');
+      });
+    }
   }
 
-  LibraryElement loadLibrary(Uri uri, Node node, Uri canonicalUri) {
+  /**
+   * Create (or reuse) a library element for the library located at [uri].
+   * If a new library is created, the [handler] is notified.
+   */
+  LibraryElement createLibrary(LibraryDependencyHandler handler,
+                               Uri uri, Node node, Uri canonicalUri) {
     bool newLibrary = false;
     LibraryElement createLibrary() {
       newLibrary = true;
       Script script = compiler.readScript(uri, node);
       LibraryElement element = new LibraryElement(script, canonicalUri);
+      handler.registerNewLibrary(element);
       native.maybeEnableNative(compiler, element, uri);
       return element;
     }
@@ -159,94 +235,348 @@ class ScannerTask extends CompilerTask {
     }
     if (newLibrary) {
       compiler.withCurrentElement(library, () {
-        scanLibrary(library);
-        compiler.onLibraryLoaded(library, uri);
+        compiler.scanner.scanLibrary(library);
+        processLibraryTags(handler, library);
+        handler.registerLibraryExports(library);
+        compiler.onLibraryScanned(library, uri);
       });
     }
     return library;
   }
 
-  void importLibrary(LibraryElement library, LibraryElement imported,
-                     Import tag, [CompilationUnitElement compilationUnit]) {
-    if (!imported.hasLibraryName()) {
-      compiler.withCurrentElement(library, () {
-        compiler.reportError(tag === null ? null : tag.uri,
-                             'no #library tag found in ${imported.uri}');
-      });
-    }
-    if (tag !== null && tag.prefix !== null) {
-      SourceString prefix = tag.prefix.source;
-      Element e = library.find(prefix);
+  // TODO(johnniwinther): Remove this method when 'js_helper' is handled by
+  // [LibraryLoaderTask].
+  void importLibrary(LibraryElement importingLibrary,
+                     LibraryElement importedLibrary,
+                     Import tag) {
+    new ImportLink(tag, importedLibrary).importLibrary(compiler,
+                                                       importingLibrary);
+  }
+}
+
+
+/**
+ * The fields of this class models a state machine for checking script
+ * tags come in the correct order.
+ */
+class TagState {
+  static const int NO_TAG_SEEN = 0;
+  static const int LIBRARY = 1;
+  static const int IMPORT_OR_EXPORT = 2;
+  static const int SOURCE = 3;
+  static const int RESOURCE = 4;
+
+  /** Next state. */
+  static const List<int> NEXT =
+      const <int>[NO_TAG_SEEN,
+                  IMPORT_OR_EXPORT, // Only one library tag is allowed.
+                  IMPORT_OR_EXPORT,
+                  SOURCE,
+                  RESOURCE];
+}
+
+/**
+ * An [import] tag and the [importedLibrary] imported through [import].
+ */
+class ImportLink {
+  final Import import;
+  final LibraryElement importedLibrary;
+
+  ImportLink(this.import, this.importedLibrary);
+
+  /**
+   * Imports the library into the [importingLibrary].
+   */
+  void importLibrary(Compiler compiler, LibraryElement importingLibrary) {
+    assert(invariant(importingLibrary,
+                     importedLibrary.exportsHandled,
+                     message: 'Exports not handled on $importedLibrary'));
+    if (import !== null && import.prefix !== null) {
+      SourceString prefix = import.prefix.source;
+      Element e = importingLibrary.find(prefix);
       if (e === null) {
-        if (compilationUnit === null) {
-          compilationUnit = library.entryCompilationUnit;
-        }
-        e = new PrefixElement(prefix, compilationUnit, tag.getBeginToken());
-        library.addToScope(e, compiler);
+        e = new PrefixElement(prefix, importingLibrary.entryCompilationUnit,
+                              import.getBeginToken());
+        importingLibrary.addToScope(e, compiler);
       }
       if (e.kind !== ElementKind.PREFIX) {
         compiler.withCurrentElement(e, () {
           compiler.reportWarning(new Identifier(e.position()),
-                                 'duplicated definition');
+          'duplicated definition');
         });
-        compiler.reportError(tag.prefix, 'duplicate defintion');
+        compiler.reportError(import.prefix, 'duplicate definition');
       }
       PrefixElement prefixElement = e;
-      imported.forEachExport((Element element) {
+      importedLibrary.forEachExport((Element element) {
+        // TODO(johnniwinther): Handle show and hide combinators.
+        // TODO(johnniwinther): Clean-up like [checkDuplicateLibraryName].
         Element existing =
             prefixElement.imported.putIfAbsent(element.name, () => element);
         if (existing !== element) {
           compiler.withCurrentElement(existing, () {
             compiler.reportWarning(new Identifier(existing.position()),
-                                   'duplicated import');
+            'duplicated import');
           });
           compiler.withCurrentElement(element, () {
             compiler.reportError(new Identifier(element.position()),
-                                 'duplicated import');
+            'duplicated import');
           });
         }
       });
     } else {
-      imported.forEachExport((Element element) {
+      importedLibrary.forEachExport((Element element) {
         compiler.withCurrentElement(element, () {
-          library.addImport(element, compiler);
+          // TODO(johnniwinther): Handle show and hide combinators.
+          importingLibrary.addImport(element, compiler);
         });
       });
     }
   }
 }
 
-class DietParserTask extends CompilerTask {
-  DietParserTask(Compiler compiler) : super(compiler);
-  final String name = 'Diet Parser';
-
-  dietParse(CompilationUnitElement compilationUnit, Token tokens) {
-    measure(() {
-      Function idGenerator = compiler.getNextFreeClassId;
-      ElementListener listener =
-          new ElementListener(compiler, compilationUnit, idGenerator);
-      PartialParser parser = new PartialParser(listener);
-      parser.parseUnit(tokens);
+/**
+ * A node in the library dependency graph.
+ *
+ * This class is used to collect the library dependencies expressed through
+ * import and export tags, and as the work-list entry in computations of library
+ * exports performed in [LibraryDependencyHandler.computeExports].
+ */
+class LibraryDependencyNode {
+  final LibraryElement library;
+
+  /**
+   * A linked list of the import tags that import [library] mapped to the
+   * corresponding libraries. This is used to propagate exports into imports
+   * after the export scopes have been computed.
+   */
+  Link<ImportLink> imports = const EmptyLink<ImportLink>();
+
+  /**
+   * The export tags that export [library] mapped to the nodes for the libraries
+   * that declared each export tag. This is used to propagete exports during the
+   * computation of export scopes.
+   */
+  Map<Export, LibraryDependencyNode> dependencyMap =
+      new Map<Export, LibraryDependencyNode>();
+
+  /**
+   * The export scope for [library] which is gradually computed by the work-list
+   * computation in [LibraryDependencyHandler.computeExports].
+   */
+  Map<SourceString, Element> exportScope = new Map<SourceString, Element>();
+
+  /**
+   * The set of exported elements that need to be propageted to dependent
+   * libraries as part of the work-list computation performed in
+   * [LibraryDependencyHandler.computeExports].
+   */
+  Set<Element> pendingExportSet = new Set<Element>();
+
+  LibraryDependencyNode(LibraryElement this.library);
+
+  /**
+   * Registers that the library of this node imports [importLibrary] through the
+   * [import] tag.
+   */
+  void registerImportDependency(Import import,
+                                LibraryElement importedLibrary) {
+    imports = imports.prepend(new ImportLink(import, importedLibrary));
+  }
+
+  /**
+   * Registers that the library of this node is exported by
+   * [exportingLibraryNode] through the [export] tag.
+   */
+  void registerExportDependency(Export export,
+                                LibraryDependencyNode exportingLibraryNode) {
+    dependencyMap[export] = exportingLibraryNode;
+  }
+
+  /**
+   * Registers all non-private locally declared members of the library of this
+   * node to be exported. This forms the basis for the work-list computation of
+   * the export scopes performed in [LibraryDependencyHandler.computeExports].
+   */
+  void registerInitialExports() {
+    pendingExportSet.addAll(
+        library.localScope.getValues().filter((Element element) {
+          // At this point [localScope] only contains members so we don't need
+          // to check for foreign or prefix elements.
+          return !element.name.isPrivate();
+        }));
+  }
+
+  /**
+   * Registers the compute export scope with the node library.
+   */
+  void registerExports() {
+    library.setExports(exportScope.getValues());
+  }
+
+  /**
+   * Registers the imports of the node library.
+   */
+  void registerImports(Compiler compiler) {
+    for (ImportLink link in imports) {
+      link.importLibrary(compiler, library);
+    }
+  }
+
+  /**
+   * Copies and clears pending export set for this node.
+   */
+  List<Element> pullPendingExports() {
+    List<Element> pendingExports = new List.from(pendingExportSet);
+    pendingExportSet.clear();
+    return pendingExports;
+  }
+
+  /**
+   * Adds [element] to the export scope for this node. If the [element] name
+   * is a duplicate, an error element is inserted into the exscope.
+   */
+  Element addElementToExportScope(Compiler compiler, Element element) {
+    SourceString name = element.name;
+    Element existingElement = exportScope[name];
+    if (existingElement !== null) {
+      if (existingElement.getLibrary() != library) {
+        // Declared elements hide exported elements.
+        element = exportScope[name] = new ErroneousElement(
+            MessageKind.DUPLICATE_EXPORT, [name], name, library);
+      }
+    } else {
+      exportScope[name] = element;
+    }
+    return element;
+  }
+
+  /**
+   * Propagates the exported [element] to all library nodes that depend upon
+   * this node. If the propagation updated any pending exports, [:true:] is
+   * returned.
+   */
+  bool propagateElement(Element element) {
+    bool change = false;
+    dependencyMap.forEach((Export export, LibraryDependencyNode exportNode) {
+      if (exportNode.addElementToPendingExports(export, element)) {
+        change = true;
+      }
     });
+    return change;
+  }
+
+  /**
+   * Adds [element] to the pending exports of this node and returns [:true:] if
+   * the pending export set was modified. The combinators of [export] are used
+   * to filter the element.
+   */
+  bool addElementToPendingExports(Export export, Element element) {
+    // TODO(johnniwinther): Use [export] to handle show and hide combinators.
+    if (exportScope[element.name] !== element) {
+      if (!pendingExportSet.contains(element)) {
+        pendingExportSet.add(element);
+        return true;
+      }
+    }
+    return false;
   }
 }
 
 /**
- * The fields of this class models a state machine for checking script
- * tags come in the correct order.
+ * Helper class used for computing the possibly cyclic import/export scopes of
+ * a set of libraries.
+ *
+ * This class is used by [ScannerTask.loadLibrary] to collect all newly loaded
+ * libraries and to compute their import/export scopes through a fixed-point
+ * algorithm.
  */
-class TagState {
-  static const int NO_TAG_SEEN = 0;
-  static const int LIBRARY = 1;
-  static const int IMPORT = 2;
-  static const int SOURCE = 3;
-  static const int RESOURCE = 4;
+class LibraryDependencyHandler {
+  final Compiler compiler;
 
-  /** Next state. */
-  static const List<int> NEXT =
-      const <int>[NO_TAG_SEEN,
-                  IMPORT, // Only one library tag is allowed.
-                  IMPORT,
-                  SOURCE,
-                  RESOURCE];
+  /**
+   * Newly loaded libraries and their corresponding node in the library
+   * dependency graph. Libraries that have already been fully loaded are not
+   * part of the dependency graph of this handler since their export scopes have
+   * already been computed.
+   */
+  Map<LibraryElement,LibraryDependencyNode> nodeMap =
+      new Map<LibraryElement,LibraryDependencyNode>();
+
+  LibraryDependencyHandler(Compiler this.compiler);
+
+  /**
+   * Performs a fixed-point computation on the export scopes of all registered
+   * libraries and creates the import/export of the libraries based on the
+   * fixed-point.
+   */
+  void computeExports() {
+    bool changed = true;
+    while (changed) {
+      changed = false;
+      nodeMap.forEach((_, LibraryDependencyNode node) {
+        var pendingExports = node.pullPendingExports();
+        pendingExports.forEach((Element element) {
+          element = node.addElementToExportScope(compiler, element);
+          if (node.propagateElement(element)) {
+            changed = true;
+          }
+        });
+      });
+    }
+
+    // Setup export scopes. These have to be set before computing the import
+    // scopes to avoid accessing uncomputed export scopes during handling of
+    // imports.
+    nodeMap.forEach((LibraryElement library, LibraryDependencyNode node) {
+      node.registerExports();
+    });
+
+    // Setup import scopes.
+    nodeMap.forEach((LibraryElement library, LibraryDependencyNode node) {
+      node.registerImports(compiler);
+    });
+  }
+
+  /**
+   * Registers that [library] depends on [loadedLibrary] through [tag].
+   */
+  void registerDependency(LibraryElement library,
+                          LibraryDependency tag,
+                          LibraryElement loadedLibrary) {
+    if (tag is Export) {
+      // [loadedLibrary] is exported by [library].
+      if (loadedLibrary.exportsHandled) {
+        // Export scope already computed on [loadedLibrary].
+        return;
+      }
+      LibraryDependencyNode exportedNode = nodeMap[loadedLibrary];
+      LibraryDependencyNode exportingNode = nodeMap[library];
+      assert(invariant(loadedLibrary, exportedNode != null,
+          message: "$loadedLibrary has not been registered"));
+      assert(invariant(library, exportingNode != null,
+          message: "$library has not been registered"));
+      exportedNode.registerExportDependency(tag, exportingNode);
+    } else if (tag == null || tag is Import) {
+      // [loadedLibrary] is imported by [library].
+      LibraryDependencyNode importingNode = nodeMap[library];
+      assert(invariant(library, importingNode != null,
+          message: "$library has not been registered"));
+      importingNode.registerImportDependency(tag, loadedLibrary);
+    }
+  }
+
+  /**
+   * Registers [library] for the processing of its import/export scope.
+   */
+  void registerNewLibrary(LibraryElement library) {
+    nodeMap[library] = new LibraryDependencyNode(library);
+  }
+
+  /**
+   * Registers all top-level entities of [library] as starting point for the
+   * fixed-point computation of the import/export scopes.
+   */
+  void registerLibraryExports(LibraryElement library) {
+    nodeMap[library].registerInitialExports();
+  }
 }