Reapply "Add TypeVariable object on runtime to support reflection on type variables." and "Fix type…

sdk/lib/_internal/compiler/implementation/js_backend/type_variable_handler.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/type_variable_handler.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/type_variable_handler.dart b/sdk/lib/_internal/compiler/implementation/js_backend/type_variable_handler.dart
new file mode 100644
index 0000000000000000000000000000000000000000..8cddea717845ad65bc7dc80957810f5e183315d7
--- /dev/null
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/type_variable_handler.dart
@@ -0,0 +1,143 @@
+// Copyright (c) 2013, 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.
+
+part of js_backend;
+
+/**
+ * Handles construction of TypeVariable constants needed at runtime.
+ */
+class TypeVariableHandler {
+  JavaScriptBackend backend;
+  FunctionElement typeVariableConstructor;
+  CompileTimeConstantEvaluator evaluator;
+
+  /**
+   * Contains all instantiated classes that have type variables and are needed
+   * for reflection.
+   */
+  List<ClassElement> typeVariableClasses = new List<ClassElement>();
+
+  /**
+   *  Maps a class element to a list with indices that point to type variables
+   *  constants for each of the class' type variables.
+   */
+  Map<ClassElement, List<int>> typeVariables =
+      new Map<ClassElement, List<int>>();
+
+  /**
+   *  Maps a TypeVariableType to the index pointing to the constant representing
+   *  the corresponding type variable at runtime.
+   */
+  Map<TypeVariableElement, int> typeVariableConstants =
+      new Map<TypeVariableElement, int>();
+
+  TypeVariableHandler(this.backend);
+
+  ClassElement get typeVariableClass => backend.typeVariableClass;
+  CodeEmitterTask get task => backend.emitter;
+  MetadataEmitter get emitter => task.metadataEmitter;
+  Compiler get compiler => backend.compiler;
+
+  void registerClassWithTypeVariables(ClassElement cls) {
+    typeVariableClasses.add(cls);
+  }
+
+  void onResolutionQueueEmpty(Enqueuer enqueuer) {
+    if (typeVariableConstructor == null) {
+      if (!typeVariableClass.constructors.isEmpty &&
+          !typeVariableClass.constructors.tail.isEmpty) {
+        compiler.reportInternalError(
+            typeVariableClass,
+            'Class $typeVariableClass should only have one constructor');
+      }
+      typeVariableConstructor = typeVariableClass.constructors.head;
+      backend.enqueueClass(
+          enqueuer, typeVariableClass, compiler.globalDependencies);
+      backend.enqueueInResolution(
+          typeVariableConstructor, compiler.globalDependencies);
+    }
+  }
+
+  void onCodegenQueueEmpty() {
+    evaluator = new CompileTimeConstantEvaluator(
+        compiler.constantHandler, compiler.globalDependencies, compiler);
+
+    for (ClassElement cls in typeVariableClasses) {
+      InterfaceType typeVariableType = typeVariableClass.computeType(compiler);
+      List<int> constants = <int>[];
+      for (TypeVariableType currentTypeVariable in cls.typeVariables) {
+        List<Constant> createArguments(FunctionElement constructor) {
+        if (constructor != typeVariableConstructor) {
+            compiler.internalErrorOnElement(
+                currentTypeVariable.element,
+                'Unexpected constructor $constructor');
+          }
+          Constant name = backend.constantSystem.createString(
+              new DartString.literal(currentTypeVariable.name.slowToString()),
+              null);
+          Constant bound = backend.constantSystem.createInt(
+              emitter.reifyType(currentTypeVariable.element.bound));
+          Constant type = evaluator.makeTypeConstant(cls);
+          return [type, name, bound];
+        }
+
+        Constant c = evaluator.makeConstructedConstant(
+            currentTypeVariable.element, typeVariableType,
+            typeVariableConstructor, createArguments);
+        backend.registerCompileTimeConstant(c, compiler.globalDependencies);
+        compiler.constantHandler.addCompileTimeConstantForEmission(c);
+        constants.add(
+            reifyTypeVariableConstant(c, currentTypeVariable.element));
+      }
+      typeVariables[cls] = constants;
+    }
+    typeVariableClasses.clear();
+  }
+
+  /**
+   * Adds [c] to [emitter.globalMetadata] and returns the index pointing to
+   * the entry.
+   *
+   * If the corresponding type variable has already been encountered an
+   * entry in the list has already been reserved and the constant is added
+   * there, otherwise a new entry for [c] is created.
+   */
+  int reifyTypeVariableConstant(Constant c, TypeVariableElement variable) {
+    String name =
+        jsAst.prettyPrint(task.constantReference(c), compiler).getText();
+    int index;
+    if (typeVariableConstants.containsKey(variable)) {
+      index = typeVariableConstants[variable];
+      emitter.globalMetadata[index] = name;
+    } else {
+      index = emitter.addGlobalMetadata(name);
+      typeVariableConstants[variable] = index;
+    }
+    return index;
+  }
+
+  /**
+   * Returns the index pointing to the constant in [emitter.globalMetadata]
+   * representing this type variable
+   *.
+   *
+   * If the constant has not yet been constructed, an entry is  allocated in
+   * the global metadata list and the index pointing to this entry is returned.
+   * When the corresponding constant is constructed later,
+   * [reifyTypeVariableConstant] will be called and the constant will be added
+   * on the allocated entry.
+   */
+  int reifyTypeVariable(TypeVariableElement variable) {
+    if (typeVariableConstants.containsKey(variable)) {
+      return typeVariableConstants[variable];
+    }
+
+    emitter.globalMetadata.add('Placeholder for ${variable}');
+    return typeVariableConstants[variable] = emitter.globalMetadata.length - 1;
+  }
+
+  List<int> typeVariablesOf(ClassElement classElement) {
+    return typeVariables[classElement];
+  }
+}