Support user generated custom native JS classes.

pkg/compiler/lib/src/js_backend/js_interop_analysis.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.
+
+/// Analysis to determine how to generate code for typed JavaScript interop.
+library compiler.src.js_backend.js_interop_analysis;
+
+import '../common/names.dart' show Identifiers;
+import '../compiler.dart' show Compiler;
+import '../diagnostics/messages.dart' show MessageKind;
+import '../constants/values.dart'
+    show
+        ConstantValue,
+        ConstructedConstantValue,
+        ListConstantValue,
+        NullConstantValue,
+        StringConstantValue,
+        TypeConstantValue;
+import '../elements/elements.dart'
+    show
+        ClassElement,
+        Element,
+        FieldElement,
+        FunctionElement,
+        LibraryElement,
+        MetadataAnnotation;
+
+import '../js/js.dart' as jsAst;
+import '../js/js.dart' show js;
+import '../universe/selector.dart' show Selector;
+import '../universe/universe.dart' show SelectorConstraints;
+
+import 'js_backend.dart' show JavaScriptBackend;
+
+class JsInteropAnalysis {
+  final JavaScriptBackend backend;
+
+  /// The resolved [FieldElement] for `Js.name`.
+  FieldElement nameField;
+  bool enabledJsInterop = false;
+
+  /// Whether the backend is currently processing the codegen queue.
+  bool _inCodegen = false;
+
+  JsInteropAnalysis(this.backend);
+
+  void onQueueClosed() {
+    if (_inCodegen) return;
+
+    if (backend.jsAnnotationClass != null) {
+      nameField = backend.jsAnnotationClass.lookupMember('name');
+      backend.compiler.libraryLoader.libraries
+          .forEach(processJsInteropAnnotationsInLibrary);
+    }
+  }
+
+  void onCodegenStart() {
+    _inCodegen = true;
+  }
+
+  void processJsInteropAnnotation(Element e) {
+    for (MetadataAnnotation annotation in e.implementation.metadata) {
+      ConstantValue constant = backend.compiler.constants.getConstantValue(
+          annotation.constant);
+      if (constant == null || constant is! ConstructedConstantValue) continue;
+      ConstructedConstantValue constructedConstant = constant;
+      if (constructedConstant.type.element == backend.jsAnnotationClass) {
+        ConstantValue value = constructedConstant.fields[nameField];
+        if (value.isString) {
+          StringConstantValue stringValue = value;
+          e.setJsInteropName(stringValue.primitiveValue.slowToString());
+        } else {
+          assert(value.isNull);

[sra1, 2015/10/13 03:31:36]

    @Js(1)
    external method();

Should generate an assignability warning, but is still valid 'Dart' code.
Should probably generate another warning or error and not assert.

+          e.setJsInteropName('');
+        }
+        enabledJsInterop = true;
+        return;
+      }
+    }
+  }
+
+  void processJsInteropAnnotationsInLibrary(LibraryElement library) {
+    processJsInteropAnnotation(library);
+    library.implementation.forEachLocalMember((Element element) {
+      processJsInteropAnnotation(element);
+      if (!element.isClass || !element.isJsInterop) return;
+
+      ClassElement classElement = element;
+
+      if (!classElement
+          .implementsInterface(backend.jsJavaScriptObjectClass)) {
+        backend.compiler.reportErrorMessage(classElement,
+            MessageKind.JS_INTEROP_CLASS_CANNOT_EXTEND_DART_CLASS, {
+          'cls': classElement.name,
+          'superclass': classElement.superclass.name
+        });
+      }
+
+      classElement.forEachMember(
+          (ClassElement classElement, Element member) {
+        processJsInteropAnnotation(member);
+
+        if (!member.isSynthesized &&
+            classElement.isJsInterop &&
+            member is FunctionElement) {
+          FunctionElement fn = member;
+          if (!fn.isExternal && !fn.isAbstract) {
+            backend.compiler.reportErrorMessage(
+                fn,
+                MessageKind.JS_INTEROP_CLASS_NON_EXTERNAL_MEMBER,
+                {'cls': classElement.name, 'member': member.name});
+          }
+        }
+      });
+    });
+  }
+
+  jsAst.Statement buildJsInteropBootstrap() {
+    if (!enabledJsInterop) return null;
+    List<jsAst.Statement> statements = <jsAst.Statement>[];
+    backend.compiler.codegenWorld.forEachInvokedName(
+        (String name, Map<Selector, SelectorConstraints> selectors) {
+      selectors.forEach((Selector selector, SelectorConstraints constraints) {
+        if (selector.isClosureCall) {
+          // TODO(jacobr): support named arguments.
+          if (selector.namedArgumentCount > 0) return;
+          int argumentCount = selector.argumentCount;
+          var candidateParameterNames =
+              'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLOMOPQRSTUVWXYZ';
+          var parameters = new List<String>.generate(
+              argumentCount, (i) => candidateParameterNames[i]);
+
+          var name = backend.namer.invocationName(selector);
+          statements.add(js.statement(
+              'Function.prototype.# = function(#) { return this(#) }',
+              [name, parameters, parameters]));
+        }
+      });
+    });
+    return new jsAst.Block(statements);
+  }
+}