Implement is-checks against type variables.

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

Index: sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart b/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
index f805355f634bccc366b0574aedde8def7f8eedd6..d994ae31fed58c7c0bd34f89bcd5cfde318464d7 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
@@ -99,6 +99,17 @@ class CodeEmitterTask extends CompilerTask {
   Set<ClassElement> checkedClasses;
 
   /**
+   * Set of JS native classes (or 'Object') that need a [:$nativeCheck:] method,
+   * because they could be used as a type argument in an is-check.
+   *
+   * For example, in the following program, the class int needs a native check
+   * to correctly match integers in the is-check:
+   *   class Check<T> { foo(o) => o is T; }
+   *   main() => new Check<int>().foo(3);
+   */
+  Set<ClassElement> requiredNativeChecks;
+
+  /**
    * Raw Typedef symbols occuring in is-checks and type assertions.  If the
    * program contains `x is F<int>` and `x is F<bool>` then the TypedefElement
    * `F` will occur once in [checkedTypedefs].
@@ -107,6 +118,17 @@ class CodeEmitterTask extends CompilerTask {
 
   final bool generateSourceMap;
 
+  Iterable<ClassElement> cachedClassesUsingTypeVariableTests;
+
+  Iterable<ClassElement> get classesUsingTypeVariableTests {
+    if (cachedClassesUsingTypeVariableTests == null) {
+      cachedClassesUsingTypeVariableTests = backend.rti.isChecks
+          .where((DartType t) => t is TypeVariableType)
+          .map((TypeVariableType v) => v.element.getEnclosingClass());
+    }
+    return cachedClassesUsingTypeVariableTests;
+  }
+
   CodeEmitterTask(Compiler compiler, Namer namer, this.generateSourceMap)
       : boundClosureBuffer = new CodeBuffer(),
         mainBuffer = new CodeBuffer(),
@@ -119,7 +141,44 @@ class CodeEmitterTask extends CompilerTask {
   }
 
   void computeRequiredTypeChecks() {
-    assert(checkedClasses == null);
+    assert(checkedClasses == null &&
+           checkedTypedefs == null &&
+           requiredNativeChecks == null);
+
+    // Compute type arguments of classes that potentially use their type
+    // variables in is-checks and compute the (small) set of classes that
+    // need native check methods (consult the documentation of
+    // [requiredNativeChecks] for more information).
+    requiredNativeChecks = new Set<ClassElement>();
+    Iterable<ClassElement> classes = classesUsingTypeVariableTests;
+    if (!classes.isEmpty) {
+      // Find all instantiated types that are a subtype of a class that uses
+      // one of its type arguments in an is-check and add the arguments to the
+      // set of is-checks.
+      // TODO(karlklose): replace this with code that uses a subtype lookup
+      // datastructure in the world.
+      for (DartType type in compiler.codegenWorld.instantiatedTypes) {
+        if (type.kind != TypeKind.INTERFACE) continue;
+        InterfaceType classType = type;
+        for (ClassElement cls in classes) {
+          // We need the type as instance of its superclass anyway, so we just
+          // try to compute the substitution; if the result is [:null:], the
+          // classes are not related.
+          InterfaceType instance = classType.asInstanceOf(cls);
+          if (instance == null) continue;
+          Link<DartType> typeArguments = instance.typeArguments;
+          for (DartType argument in typeArguments) {
+            Element element = argument.element;
+            JavaScriptBackend backend = compiler.backend;
+            if (backend.rti.needsNativeCheck(element)) {
+              requiredNativeChecks.add(element);
+            }
+            compiler.codegenWorld.isChecks.add(argument);
+          }
+        }
+      }
+    }
+
     checkedClasses = new Set<ClassElement>();
     checkedTypedefs = new Set<TypedefElement>();
     compiler.codegenWorld.isChecks.forEach((DartType t) {
@@ -1075,7 +1134,7 @@ class CodeEmitterTask extends CompilerTask {
 
     void generateIsTest(Element other) {
       jsAst.Expression code;
-      if (compiler.objectClass == other) return;
+      if (other == compiler.objectClass) return;
       if (nativeEmitter.requiresNativeIsCheck(other)) {
         code = js.fun([], [js.return_(true)]);
       } else {
@@ -1136,7 +1195,7 @@ class CodeEmitterTask extends CompilerTask {
     }
   }
 
-  void emitRuntimeClassesAndTests(CodeBuffer buffer) {
+  void emitRuntimeTypeSupport(CodeBuffer buffer) {
     RuntimeTypeInformation rti = backend.rti;
     TypeChecks typeChecks = rti.getRequiredChecks();
 
@@ -1155,8 +1214,7 @@ class CodeEmitterTask extends CompilerTask {
       if (!needsHolder(cls)) return;
       String holder = namer.isolateAccess(cls);
       String name = namer.getName(cls);
-      buffer.add("$holder$_=$_{builtin\$cls:$_'$name'");
-      buffer.add('}$N');
+      buffer.add("$holder$_=$_{builtin\$cls:$_'$name'}$N");
     }
 
     // Create representation objects for classes that we do not have a class
@@ -1177,6 +1235,16 @@ class CodeEmitterTask extends CompilerTask {
         }
       };
     }
+
+    // Emit native check methods for the class representations of native types
+    // that could be used in an is-check against a type variable.
+    requiredNativeChecks.forEach((ClassElement cls) {
+      jsAst.Expression nativeCheck = rti.getNativeCheck(cls);
+      String holder = namer.isolateAccess(cls);
+      buffer.add('$holder.${namer.getNativeCheckName()}$_=$_');
+      buffer.addBuffer(jsAst.prettyPrint(nativeCheck, compiler));
+      buffer.add('$N');
+    });
   }
 
   void visitNativeMixins(ClassElement classElement,
@@ -1565,6 +1633,11 @@ class CodeEmitterTask extends CompilerTask {
         emitted.add(superclass);
       }
       for (DartType supertype in cls.allSupertypes) {
+        ClassElement superclass = supertype.element;
+        if (classesUsingTypeVariableTests.contains(superclass)) {
+          emitSubstitution(superclass, emitNull: true);
+          emitted.add(superclass);
+        }
         for (ClassElement check in checkedClasses) {
           if (supertype.element == check && !emitted.contains(check)) {
             // Generate substitution.  If no substitution is necessary, emit
@@ -2582,7 +2655,6 @@ if (typeof document !== 'undefined' && document.readyState !== 'complete') {
   String assembleProgram() {
     measure(() {
       computeNeededClasses();
-
       mainBuffer.add(GENERATED_BY);
       if (!compiler.enableMinification) mainBuffer.add(HOOKS_API_USAGE);
       mainBuffer.add('function ${namer.isolateName}()$_{}\n');
@@ -2603,7 +2675,7 @@ if (typeof document !== 'undefined' && document.readyState !== 'complete') {
       // We need to finish the classes before we construct compile time
       // constants.
       emitFinishClassesInvocationIfNecessary(mainBuffer);
-      emitRuntimeClassesAndTests(mainBuffer);
+      emitRuntimeTypeSupport(mainBuffer);
       emitCompileTimeConstants(mainBuffer);
       // Static field initializations require the classes and compile-time
       // constants to be set up.