implement top-level JS annotated getters

lib/src/compiler/code_generator.dart

Index: lib/src/compiler/code_generator.dart
diff --git a/lib/src/compiler/code_generator.dart b/lib/src/compiler/code_generator.dart
index 8a97a278c6114a34e3a048de9a9dd36cedc82799..e6453263e95f46b0676c1633cf63880efac3b18f 100644
--- a/lib/src/compiler/code_generator.dart
+++ b/lib/src/compiler/code_generator.dart
@@ -81,8 +81,12 @@ class CodeGenerator extends GeneralizingAstVisitor
   /// 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>>();
@@ -226,8 +230,12 @@ class CodeGenerator extends GeneralizingAstVisitor
       }
 
       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.

       }
     }
 
@@ -276,6 +284,39 @@ class CodeGenerator extends GeneralizingAstVisitor
     }
   }
 
+  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.
@@ -2341,13 +2382,8 @@ class CodeGenerator extends GeneralizingAstVisitor
   }
 
   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));
@@ -3039,11 +3075,8 @@ class CodeGenerator extends GeneralizingAstVisitor
   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);