[dart2js] Propagate kernel variance to emit annotations in RTI table.

Change-Id: I4612c50828f5d85115e15838e2cc2117446b07ca
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127201
Reviewed-by: Mayank Patke <fishythefish@google.com>
Commit-Queue: Kallen Tu <kallentu@google.com>

Author: kallentu

pkg/compiler/lib/src/common_elements.dart

@@ -504,6 +504,7 @@ abstract class CommonElements {
   FunctionEntity get rtiBindMethod;
   FunctionEntity get rtiAddRulesMethod;
   FunctionEntity get rtiAddErasedTypesMethod;
+  FunctionEntity get rtiAddTypeParameterVariancesMethod;
 
   FunctionEntity get generalIsTestImplementation;
   FunctionEntity get generalAsCheckImplementation;
@@ -1943,6 +1944,12 @@ class CommonElementsImpl
   FunctionEntity get rtiAddErasedTypesMethod => _rtiAddErasedTypesMethod ??=
       _findClassMember(_rtiUniverseClass, 'addErasedTypes');
 
+  FunctionEntity _rtiAddTypeParameterVariancesMethod;
+  @override
+  FunctionEntity get rtiAddTypeParameterVariancesMethod =>
+      _rtiAddTypeParameterVariancesMethod ??=
+          _findClassMember(_rtiUniverseClass, 'addTypeParameterVariances');
+
   FunctionEntity _generalIsTestImplementation;
   @override
   FunctionEntity get generalIsTestImplementation =>
@@ -2305,6 +2312,9 @@ abstract class ElementEnvironment {
   /// `Object`.
   DartType getTypeVariableBound(TypeVariableEntity typeVariable);
 
+  /// Returns the variances for each type parameter in [cls].
+  List<Variance> getTypeVariableVariances(ClassEntity cls);
+
   /// Returns the type of [function].
   FunctionType getFunctionType(FunctionEntity function);
 

pkg/compiler/lib/src/elements/entities.dart

@@ -219,6 +219,7 @@ class AsyncMarker {
 }
 
 /// Values for variance annotations.
+/// This needs to be kept in sync with values of `Variance` in `dart:_rti`.
 enum Variance { legacyCovariant, covariant, contravariant, invariant }
 
 /// Stripped down super interface for constructor like entities.

pkg/compiler/lib/src/js_backend/backend_impact.dart

@@ -13,6 +13,7 @@ import '../universe/world_impact.dart'
     show WorldImpact, WorldImpactBuilder, WorldImpactBuilderImpl;
 import '../universe/use.dart';
 import '../util/enumset.dart';
+import '../options.dart';
 
 /// Backend specific features required by a backend impact.
 enum BackendFeature {
@@ -90,9 +91,9 @@ class BackendImpact {
 /// The JavaScript backend dependencies for various features.
 class BackendImpacts {
   final CommonElements _commonElements;
-  final bool _newRti;
+  final CompilerOptions _options;
 
-  BackendImpacts(this._commonElements, this._newRti);
+  BackendImpacts(this._commonElements, this._options);
 
   BackendImpact _getRuntimeTypeArgument;
 
@@ -166,7 +167,7 @@ class BackendImpacts {
     return _typeVariableBoundCheck ??= new BackendImpact(staticUses: [
       _commonElements.throwTypeError,
       _commonElements.assertIsSubtype,
-      if (_newRti) _commonElements.checkTypeBound,
+      if (_options.experimentNewRti) _commonElements.checkTypeBound,
     ]);
   }
 
@@ -428,7 +429,7 @@ class BackendImpacts {
       _commonElements.typeLiteralClass
     ], staticUses: [
       _commonElements.createRuntimeType,
-      if (_newRti) _commonElements.typeLiteralMaker,
+      if (_options.experimentNewRti) _commonElements.typeLiteralMaker,
     ]);
   }
 
@@ -770,7 +771,7 @@ class BackendImpacts {
       _genericInstantiation[typeArgumentCount] ??=
           new BackendImpact(staticUses: [
         _commonElements.getInstantiateFunction(typeArgumentCount),
-        ..._newRti
+        ..._options.experimentNewRti
             ? [
                 _commonElements.instantiatedGenericFunctionTypeNewRti,
                 _commonElements.closureFunctionType
@@ -785,7 +786,7 @@ class BackendImpacts {
 
   /// Backend impact for --experiment-new-rti.
   List<BackendImpact> newRtiImpacts(String what) {
-    if (!_newRti) return [];
+    if (!_options.experimentNewRti) return [];
     // TODO(sra): Split into refined impacts.
     return [
       BackendImpact(staticUses: [
@@ -825,9 +826,12 @@ class BackendImpacts {
 
   BackendImpact _rtiAddRules;
 
+  // TODO(fishythefish): Split into refined impacts.
   BackendImpact get rtiAddRules => _rtiAddRules ??= BackendImpact(globalUses: [
         _commonElements.rtiAddRulesMethod,
-        _commonElements.rtiAddErasedTypesMethod
+        _commonElements.rtiAddErasedTypesMethod,
+        if (_options.enableVariance)
+          _commonElements.rtiAddTypeParameterVariancesMethod,
       ], otherImpacts: [
         _needsString('Needed to encode the new RTI ruleset.')
       ]);

pkg/compiler/lib/src/js_backend/codegen_listener.dart

@@ -128,6 +128,11 @@ class CodegenEnqueuerListener extends EnqueuerListener {
           _commonElements.rtiAddRulesMethod, CallStructure.TWO_ARGS));
       newRtiImpact.registerStaticUse(StaticUse.staticInvoke(
           _commonElements.rtiAddErasedTypesMethod, CallStructure.TWO_ARGS));
+      if (_options.enableVariance) {
+        newRtiImpact.registerStaticUse(StaticUse.staticInvoke(
+            _commonElements.rtiAddTypeParameterVariancesMethod,
+            CallStructure.TWO_ARGS));
+      }
       enqueuer.applyImpact(newRtiImpact);
       _isNewRtiUsed = true;
     }

pkg/compiler/lib/src/js_backend/runtime_types_new.dart

@@ -634,4 +634,28 @@ class RulesetEncoder {
         _colon,
         js.number(entry.value),
       ]);
+
+  jsAst.StringConcatenation encodeTypeParameterVariances(
+          Map<ClassEntity, List<Variance>> typeParameterVariances) =>
+      js.concatenateStrings([
+        _quote,
+        _leftBrace,
+        ...js.joinLiterals(
+            typeParameterVariances.entries
+                .map(_encodeTypeParameterVariancesForClass),
+            _comma),
+        _rightBrace,
+        _quote,
+      ]);
+
+  jsAst.StringConcatenation _encodeTypeParameterVariancesForClass(
+          MapEntry<ClassEntity, List<Variance>> classEntry) =>
+      js.concatenateStrings([
+        js.quoteName(_emitter.typeAccessNewRti(classEntry.key)),
+        _colon,
+        _leftBracket,
+        ...js.joinLiterals(
+            classEntry.value.map((v) => js.number(v.index)), _comma),
+        _rightBracket
+      ]);
 }

pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart

@@ -439,6 +439,9 @@ var #staticStateDeclaration = {};
 // Adds the subtype rules for the new RTI.
 #typeRules;
 
+// Adds the variance table for the new RTI.
+#variances;
+
 // Shared types need to be initialized before constants.
 #sharedTypeRtis;
 
@@ -540,6 +543,9 @@ var #typesOffset = hunkHelpers.updateTypes(#types);
 // Adds the subtype rules for the new RTI.
 #typeRules;
 
+// Adds the variance table for the new RTI.
+#variances;
+
 #sharedTypeRtis;
 // Instantiates all constants of this deferred fragment.
 // Note that the constant-holder has been updated earlier and storing the
@@ -702,6 +708,7 @@ class FragmentEmitter {
       'embeddedGlobalsPart2':
           emitEmbeddedGlobalsPart2(program, deferredLoadingState),
       'typeRules': emitTypeRules(fragment),
+      'variances': emitVariances(fragment),
       'sharedTypeRtis':
           _options.experimentNewRti ? TypeReferenceResource() : [],
       'nativeSupport': program.needsNativeSupport
@@ -786,6 +793,7 @@ class FragmentEmitter {
     var tearOffs = emitInstallTearOffs(fragment);
     var constants = emitConstants(fragment);
     var typeRules = emitTypeRules(fragment);
+    var variances = emitVariances(fragment);
     var staticNonFinalFields = emitStaticNonFinalFields(fragment);
     var lazyInitializers = emitLazilyInitializedStatics(fragment);
     // TODO(floitsch): only call emitNativeSupport if we need native.
@@ -828,6 +836,7 @@ class FragmentEmitter {
       'aliases': methodAliases,
       'tearOffs': tearOffs,
       'typeRules': typeRules,
+      'variances': variances,
       'constants': constants,
       'staticNonFinalFields': staticNonFinalFields,
       'lazyStatics': lazyInitializers,
@@ -2041,6 +2050,41 @@ class FragmentEmitter {
     return js.Block(statements);
   }
 
+  js.Statement emitVariances(Fragment fragment) {
+    if (!_options.enableVariance || !_options.experimentNewRti) {
+      return js.EmptyStatement();
+    }
+
+    Map<ClassEntity, List<Variance>> typeParameterVariances = {};
+    Iterable<Class> classes =
+        fragment.libraries.expand((Library library) => library.classes);
+    classes.forEach((Class cls) {
+      ClassEntity element = cls.element;
+      List<Variance> classVariances =
+          _elementEnvironment.getTypeVariableVariances(element);
+
+      // Emit variances for a class only if there is at least one explicit
+      // variance defined.
+      bool hasOnlyLegacyVariance = classVariances
+          .every((variance) => variance == Variance.legacyCovariant);
+      if (!hasOnlyLegacyVariance) {
+        typeParameterVariances[element] = classVariances;
+      }
+    });
+
+    if (typeParameterVariances.isNotEmpty) {
+      FunctionEntity addVariances =
+          _closedWorld.commonElements.rtiAddTypeParameterVariancesMethod;
+      return js.js.statement('#(init.#,JSON.parse(#));', [
+        _emitter.staticFunctionAccess(addVariances),
+        RTI_UNIVERSE,
+        _rulesetEncoder.encodeTypeParameterVariances(typeParameterVariances),
+      ]);
+    }
+
+    return js.EmptyStatement();
+  }
+
   /// Returns an expression that creates the initial Rti Universe.
   ///
   /// This needs to be kept in sync with `_Universe.create` in `dart:_rti`.

pkg/compiler/lib/src/js_model/closure.dart

@@ -897,7 +897,7 @@ class RecordClassData implements JClassData {
   InterfaceType get instantiationToBounds => thisType;
 
   @override
-  List<Variance> getVariances() => null;
+  List<Variance> getVariances() => [];
 }
 
 /// A container for variables declared in a particular scope that are accessed

pkg/compiler/lib/src/js_model/element_map_impl.dart

@@ -2294,6 +2294,11 @@ class JsElementEnvironment extends ElementEnvironment
     return elementMap.getTypeVariableBound(typeVariable);
   }
 
+  @override
+  List<Variance> getTypeVariableVariances(ClassEntity cls) {
+    return elementMap.getTypeVariableVariances(cls);
+  }
+
   @override
   DartType getTypeVariableDefaultType(TypeVariableEntity typeVariable) {
     return elementMap._getTypeVariableDefaultType(typeVariable);

pkg/compiler/lib/src/js_model/js_strategy.dart

@@ -252,7 +252,7 @@ class JsBackendStrategy implements BackendStrategy {
     ElementEnvironment elementEnvironment = closedWorld.elementEnvironment;
     CommonElements commonElements = closedWorld.commonElements;
     BackendImpacts impacts =
-        new BackendImpacts(commonElements, _compiler.options.experimentNewRti);
+        new BackendImpacts(commonElements, _compiler.options);
     _customElementsCodegenAnalysis = new CustomElementsCodegenAnalysis(
         commonElements, elementEnvironment, closedWorld.nativeData);
     return new CodegenEnqueuer(
@@ -306,8 +306,8 @@ class JsBackendStrategy implements BackendStrategy {
     emitterTask.createEmitter(_namer, codegen, closedWorld);
     // TODO(johnniwinther): Share the impact object created in
     // createCodegenEnqueuer.
-    BackendImpacts impacts = new BackendImpacts(
-        closedWorld.commonElements, _compiler.options.experimentNewRti);
+    BackendImpacts impacts =
+        new BackendImpacts(closedWorld.commonElements, _compiler.options);
 
     _codegenImpactTransformer = new CodegenImpactTransformer(
         closedWorld,

pkg/compiler/lib/src/kernel/element_map_impl.dart

@@ -1749,6 +1749,11 @@ class KernelElementEnvironment extends ElementEnvironment
     return elementMap.getTypeVariableBound(typeVariable);
   }
 
+  @override
+  List<Variance> getTypeVariableVariances(ClassEntity cls) {
+    return elementMap.getTypeVariableVariances(cls);
+  }
+
   @override
   InterfaceType createInterfaceType(
       ClassEntity cls, List<DartType> typeArguments) {