implement top-level JS annotated getters

lib/src/compiler/code_generator.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:collection' show HashMap, HashSet;
 import 'dart:math' show min, max;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart' show Token, TokenType;
@@ skipping 63 matching lines @@
   /// Usually a [SimpleIdentifier], but it can also be other expressions
   /// that are safe to evaluate multiple times, such as `this`.
   Expression _cascadeTarget;
 
   /// The variable for the current catch clause
   SimpleIdentifier _catchParameter;
 
   /// In an async* function, this represents the stream controller parameter.
   JS.TemporaryId _asyncStarController;
 
-  /// The top-level reference to 'self' if this is a library tagged with @JS()
-  JS.TemporaryId _self;
+  /// A mapping of libraries to the contents of their corresponding
+  /// library-level @JS() annotation, if the library is annotated. The
+  /// @JS annotation contains a dot-separated identifier or is empty. The
+  /// library is then associated with a list of Strings, which represents
+  /// the list of dotted identifiers.
+  final _libraryJsPrefixes = new HashMap<LibraryElement, List<String>>();

[Jennifer Messerly, 2016/05/19 17:38:04]

BTW, we're not consistent yet, but naming convention here should be uppercase
"JS", in other words, _libraryJSPrefixes

https://www.dartlang.org/effective-dart/style/#do-capitalize-acronyms-and-abb...

[Harry Terkelsen, 2016/05/19 18:10:10]

Done.

 
   final _privateNames =
       new HashMap<LibraryElement, HashMap<String, JS.TemporaryId>>();
   final _initializingFormalTemps =
       new HashMap<ParameterElement, JS.TemporaryId>();
 
   final _dartxVar = new JS.Identifier('dartx');
   final _runtimeLibVar = new JS.Identifier('dart');
   final namedArgumentTemp = new JS.TemporaryId('opts');
 
@@ skipping 123 matching lines @@
           js.call('const # = Object.create(null)', [libraryTemp])));
 
       // dart:_runtime has a magic module that holds extenstion method symbols.
       // TODO(jmesserly): find a cleaner design for this.
       if (_isDartRuntime(library)) {
         items.add(new JS.ExportDeclaration(
             js.call('const # = Object.create(null)', [_dartxVar])));
       }
 
       if (findAnnotation(library, isPublicJSAnnotation) != null) {
-        _self = new JS.TemporaryId('self');
-        items.add(js.statement('const # = window;', [_self]));
+        var libraryJsPrefix = <String>[];
+        var prefix = getAnnotationName(library, isPublicJSAnnotation);
+        if (prefix != null && !prefix.isEmpty) {
+          libraryJsPrefix.addAll(prefix.split('.'));
+        }
+        _libraryJsPrefixes[library] = libraryJsPrefix;

[Jennifer Messerly, 2016/05/19 17:38:04]

I think you'll need to compute these on-demand, below in
_getJSName/_emitJSInterop. The problem is a case like this:

    import 'package:jquery/jquery.js'; // uses @JS interop
    main() {
      $('p').hide();
    }

If "package:jquery" is coming from a summary, we won't find it in our list of
compile units.

[Harry Terkelsen, 2016/05/19 18:10:10]

Done.

       }
     }
 
     // Collect all Element -> Node mappings, in case we need to forward declare
     // any nodes.
     var nodes = new HashMap<Element, AstNode>.identity();
     var sdkBootstrappingFns = new List<FunctionElement>();
     for (var unit in compilationUnits) {
       if (_isDartRuntime(unit.element.library)) {
         sdkBootstrappingFns.addAll(unit.element.functions);
@@ skipping 28 matching lines @@
     switch (options.moduleFormat) {
       case ModuleFormat.legacy:
         return new LegacyModuleBuilder().build(module);
       case ModuleFormat.node:
         return new NodeModuleBuilder().build(module);
       case ModuleFormat.es6:
         return module;
     }
   }
 
+  String _getJsName(Element e) {

[Jennifer Messerly, 2016/05/19 17:38:04]

_getJSName

[Harry Terkelsen, 2016/05/19 18:10:10]

Done.

+    if (!_libraryJsPrefixes.containsKey(e.library)) return null;

[Jennifer Messerly, 2016/05/19 17:38:04]

I think this is where you can implement the cache, if it's needed. It may or may
not be worth caching these. 

I'm not sure how quick a lookup is via findAnnotation. It might be fast enough
assuming most libraries don't have library-level metadata.

Ultimately I think we'll have to discuss with Analyzer folks to get a faster way
to access info like this when the summary is deserialized.

[Harry Terkelsen, 2016/05/19 18:10:10]

Done.

+    if (findAnnotation(e, isPublicJSAnnotation) != null) {
+      return getAnnotationName(e, isPublicJSAnnotation) ?? '';
+    }
+    if (e is TopLevelVariableElement &&
+        e.getter != null &&
+        (e.getter.isExternal ||
+            findAnnotation(e.getter, isPublicJSAnnotation) != null)) {
+      return getAnnotationName(e.getter, isPublicJSAnnotation) ?? '';
+    }
+    return null;
+  }
+
+  JS.Expression _emitJsInterop(Element e) {

[Jennifer Messerly, 2016/05/19 17:38:05]

_emitJSInterop

[Harry Terkelsen, 2016/05/19 18:10:10]

Done.

+    var jsName = _getJsName(e);
+    if (jsName == null) return null;
+    var name;
+    if (jsName.isEmpty) {
+      name = [e.name];
+    } else {
+      name = jsName.split('.');
+    }
+    var fullName = ['global']
+      ..addAll(_libraryJsPrefixes[e.library])
+      ..addAll(name);
+    var access = _runtimeLibVar;
+    for (var part in fullName) {
+      access = new JS.PropertyAccess(access, js.string(part));
+    }
+    return access;
+  }
+
   /// Flattens blocks in [items] to a single list.
   ///
   /// This will not flatten blocks that are marked as being scopes.
   void _copyAndFlattenBlocks(
       List<JS.ModuleItem> result, Iterable<JS.ModuleItem> items) {
     for (var item in items) {
       if (item is JS.Block && !item.isScope) {
         _copyAndFlattenBlocks(result, item.statements);
       } else {
         result.add(item);
@@ skipping 2045 matching lines @@
       if (jsArgs != null) {
         var genericName = _emitTopLevelName(element, suffix: '\$');
         return js.call('#(#)', [genericName, jsArgs]);
       }
     }
 
     return _emitTopLevelName(element);
   }
 
   JS.PropertyAccess _emitTopLevelName(Element e, {String suffix: ''}) {
-    if (e is TopLevelVariableElement &&
-        e.getter != null &&
-        findAnnotation(e.getter, isPublicJSAnnotation) != null) {
-      var annotationName = getAnnotationName(e.getter, isPublicJSAnnotation);
-      var name = js.string(annotationName ?? e.name);
-      return new JS.PropertyAccess(_self, name);
-    }
+    var interop = _emitJsInterop(e);
+    if (interop != null) return interop;
     String name = getJSExportName(e) + suffix;
     return new JS.PropertyAccess(
         emitLibraryName(e.library), _propertyName(name));
   }
 
   @override
   JS.Expression visitAssignmentExpression(AssignmentExpression node) {
     var left = node.leftHandSide;
     var right = node.rightHandSide;
     if (node.operator.type == TokenType.EQ) return _emitSet(left, right);
@@ skipping 671 matching lines @@
       return getter
           ? parent.getGetter(element.name)
           : parent.getSetter(element.name);
     }
     return null;
   }
 
   JS.Expression _emitConstructorName(
       ConstructorElement element, DartType type, SimpleIdentifier name) {
     var classElem = element.enclosingElement;
-    if (findAnnotation(classElem, isPublicJSAnnotation) != null) {
-      var annotationName = getAnnotationName(classElem, isPublicJSAnnotation);

[Jennifer Messerly, 2016/05/19 17:38:04]

fyi Siggi made a change to this in:
https://codereview.chromium.org/1998473002/diff/1/lib/src/compiler/code_gener...
(I just noticed it go by...)

-      var typeName = js.string(annotationName ?? classElem.name);
-      return new JS.PropertyAccess(_self, typeName);
-    }
+    var interop = _emitJsInterop(classElem);
+    if (interop != null) return interop;
     var typeName = _emitType(type);
     if (name != null || element.isFactory) {
       var namedCtor = _constructorName(element);
       return new JS.PropertyAccess(typeName, namedCtor);
     }
     return typeName;
   }
 
   @override
   visitConstructorName(ConstructorName node) {
@@ skipping 1432 matching lines @@
 }
 
 bool isLibraryPrefix(Expression node) =>
     node is SimpleIdentifier && node.staticElement is PrefixElement;
 
 LibraryElement _getLibrary(AnalysisContext c, String uri) =>
     c.computeLibraryElement(c.sourceFactory.forUri(uri));
 
 bool _isDartRuntime(LibraryElement l) =>
     l.isInSdk && l.source.uri.toString() == 'dart:_runtime';