dart2js: handle constant casts with type variable substitutions

Closes dart-lang/sdk#32811

Change-Id: Ibf108405a3a36092a42902e5be806310a34c067c
Reviewed-on: https://dart-review.googlesource.com/49835
Reviewed-by: Stephen Adams <[email protected]>
Commit-Queue: Sigmund Cherem <[email protected]>

Author: sigmundch

pkg/compiler/lib/src/constants/evaluation.dart

@@ -20,6 +20,9 @@ abstract class EvaluationEnvironment {
 
   DartTypes get types;
 
+  /// Type in the enclosing constructed
+  InterfaceType get enclosingConstructedType;
+
   /// Read environments string passed in using the '-Dname=value' option.
   String readFromEnvironment(String name);
 
@@ -45,8 +48,8 @@ abstract class EvaluationEnvironment {
   void reportError(
       ConstantExpression expression, MessageKind kind, Map arguments);
 
-  ConstantValue evaluateConstructor(
-      ConstructorEntity constructor, ConstantValue evaluate());
+  ConstantValue evaluateConstructor(ConstructorEntity constructor,
+      InterfaceType type, ConstantValue evaluate());
 
   ConstantValue evaluateField(FieldEntity field, ConstantValue evaluate());
 
@@ -56,6 +59,7 @@ abstract class EvaluationEnvironment {
 
 abstract class EvaluationEnvironmentBase implements EvaluationEnvironment {
   Link<Spannable> _spannableStack = const Link<Spannable>();
+  InterfaceType enclosingConstructedType;
   final Set<FieldEntity> _currentlyEvaluatedFields = new Set<FieldEntity>();
   final bool constantRequired;
 
@@ -96,10 +100,13 @@ abstract class EvaluationEnvironmentBase implements EvaluationEnvironment {
   }
 
   @override
-  ConstantValue evaluateConstructor(
-      ConstructorEntity constructor, ConstantValue evaluate()) {
+  ConstantValue evaluateConstructor(ConstructorEntity constructor,
+      InterfaceType type, ConstantValue evaluate()) {
     _spannableStack = _spannableStack.prepend(constructor);
+    var old = enclosingConstructedType;
+    enclosingConstructedType = type;
     ConstantValue result = evaluate();
+    enclosingConstructedType = old;
     _spannableStack = _spannableStack.tail;
     return result;
   }

pkg/compiler/lib/src/constants/expressions.dart

@@ -581,7 +581,8 @@ class ConstructedConstantExpression extends ConstantExpression {
   @override
   ConstantValue evaluate(
       EvaluationEnvironment environment, ConstantSystem constantSystem) {
-    return environment.evaluateConstructor(target, () {
+    InterfaceType instanceType = computeInstanceType(environment);
+    return environment.evaluateConstructor(target, instanceType, () {
       InstanceData instanceData = computeInstanceData(environment);
       if (instanceData == null) {
         return new NonConstantValue();
@@ -608,8 +609,7 @@ class ConstructedConstantExpression extends ConstantExpression {
         }
       }
       if (isValidAsConstant) {
-        return new ConstructedConstantValue(
-            computeInstanceType(environment), fieldValues);
+        return new ConstructedConstantValue(instanceType, fieldValues);
       } else {
         return new NonConstantValue();
       }
@@ -851,7 +851,12 @@ class AsConstantExpression extends ConstantExpression {
         expression.evaluate(environment, constantSystem);
     DartType expressionType =
         expressionValue.getType(environment.commonElements);
-    if (!constantSystem.isSubtype(environment.types, expressionType, type)) {
+    DartType enclosingType = environment.enclosingConstructedType;
+    DartType superType = enclosingType != null
+        ? environment.substByContext(type, enclosingType)
+        : type;
+    if (!constantSystem.isSubtype(
+        environment.types, expressionType, superType)) {
       // TODO(sigmund): consider reporting different messages and error
       // locations for implicit vs explicit casts.
       environment.reportError(expression, MessageKind.INVALID_CONSTANT_CAST,

tests/compiler/dart2js/model/constant_expression_evaluate_test.dart

@@ -97,6 +97,10 @@ class MemoryEnvironment implements EvaluationEnvironment {
   @override
   DartTypes get types => _environment.types;
 
+  @override
+  InterfaceType get enclosingConstructedType =>
+      _environment.enclosingConstructedType;
+
   void reportWarning(
       ConstantExpression expression, MessageKind kind, Map arguments) {
     errors.add(new EvaluationError(kind, arguments));
@@ -109,9 +113,10 @@ class MemoryEnvironment implements EvaluationEnvironment {
     _environment.reportError(expression, kind, arguments);
   }
 
-  ConstantValue evaluateConstructor(
-      ConstructorEntity constructor, ConstantValue evaluate()) {
-    return _environment.evaluateConstructor(constructor, evaluate);
+  @override
+  ConstantValue evaluateConstructor(ConstructorEntity constructor,
+      InterfaceType type, ConstantValue evaluate()) {
+    return _environment.evaluateConstructor(constructor, type, evaluate);
   }
 
   ConstantValue evaluateField(FieldEntity field, ConstantValue evaluate()) {

tests/language_2/const_cast3_test.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2018, 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.
+
+/// Casts in constants correctly substitute type variables.
+
+class A {
+  const A();
+}
+
+class B implements A {
+  const B();
+}
+
+class M<T extends A> {
+  final T a;
+  const M(dynamic t) : a = t; // adds implicit cast `as T`
+}
+
+main() {
+  print(const M<B>(const B()));
+}