Revert "Revert "fix #26141, add support for type arguments to constants""

pkg/analyzer/lib/src/dart/constant/evaluation.dart

Index: pkg/analyzer/lib/src/dart/constant/evaluation.dart
diff --git a/pkg/analyzer/lib/src/dart/constant/evaluation.dart b/pkg/analyzer/lib/src/dart/constant/evaluation.dart
index 57eee8973823954d54ef94305c1c0136612c826c..45c3bda38126a82d0a935f0e197f9269f2ec77ea 100644
--- a/pkg/analyzer/lib/src/dart/constant/evaluation.dart
+++ b/pkg/analyzer/lib/src/dart/constant/evaluation.dart
@@ -75,6 +75,9 @@ class ConstantEvaluationEngine {
    */
   final ConstantEvaluationValidator validator;
 
+  /** Whether we are running in strong mode. */
+  final bool strongMode;
+
   /**
    * Initialize a newly created [ConstantEvaluationEngine].  The [typeProvider]
    * is used to access known types.  [_declaredVariables] is the set of
@@ -82,9 +85,12 @@ class ConstantEvaluationEngine {
    * given, is used to verify correct dependency analysis when running unit
    * tests.
    */
-  ConstantEvaluationEngine(this.typeProvider, this._declaredVariables,
+  ConstantEvaluationEngine(TypeProvider typeProvider, this._declaredVariables,
       {ConstantEvaluationValidator validator, TypeSystem typeSystem})
-      : validator =
+      : typeProvider = typeProvider,
+        strongMode =
+            typeProvider.objectType.element.context.analysisOptions.strongMode,
+        validator =
             validator ?? new ConstantEvaluationValidator_ForProduction(),
         typeSystem = typeSystem ?? new TypeSystemImpl();
 
@@ -409,7 +415,7 @@ class ConstantEvaluationEngine {
 
   DartObjectImpl evaluateConstructorCall(
       AstNode node,
-      NodeList<Expression> arguments,
+      List<Expression> arguments,
       ConstructorElement constructor,
       ConstantVisitor constantVisitor,
       ErrorReporter errorReporter) {
@@ -515,25 +521,49 @@ class ConstantEvaluationEngine {
       // so consider it an unknown value to suppress further errors.
       return new DartObjectImpl.validWithUnknownValue(definingClass);
     }
-    HashMap<String, DartObjectImpl> fieldMap =
-        new HashMap<String, DartObjectImpl>();
+
+    // In strong mode, we allow constants to have type arguments.
+    //
+    // They will be added to the lexical environment when evaluating
+    // subexpressions.
+    HashMap<String, DartObjectImpl> typeArgumentMap;
+    if (strongMode) {
+      // Instantiate the constructor with the in-scope type arguments.
+      definingClass = constantVisitor.evaluateType(definingClass);
+      constructor = ConstructorMember.from(constructorBase, definingClass);
+
+      typeArgumentMap = new HashMap<String, DartObjectImpl>.fromIterables(
+          definingClass.typeParameters.map((t) => t.name),
+          definingClass.typeArguments.map(constantVisitor.typeConstant));
+    }
+
+    var fieldMap = new HashMap<String, DartObjectImpl>();
+    var fieldInitVisitor = new ConstantVisitor(this, errorReporter,
+        lexicalEnvironment: typeArgumentMap);
     // Start with final fields that are initialized at their declaration site.
-    for (FieldElement field in constructor.enclosingElement.fields) {
+    List<FieldElement> fields = constructor.enclosingElement.fields;
+    for (int i = 0; i < fields.length; i++) {
+      FieldElement field = fields[i];
       if ((field.isFinal || field.isConst) &&
           !field.isStatic &&
           field is ConstFieldElementImpl) {
         validator.beforeGetFieldEvaluationResult(field);
-        EvaluationResultImpl evaluationResult = field.evaluationResult;
+
+        DartObjectImpl fieldValue;
+        if (strongMode) {
+          fieldValue = field.constantInitializer.accept(fieldInitVisitor);
+        } else {
+          fieldValue = field.evaluationResult?.value;
+        }
         // It is possible that the evaluation result is null.
         // This happens for example when we have duplicate fields.
         // class Test {final x = 1; final x = 2; const Test();}
-        if (evaluationResult == null) {
+        if (fieldValue == null) {
           continue;
         }
         // Match the value and the type.
         DartType fieldType =
             FieldMember.from(field, constructor.returnType).type;
-        DartObjectImpl fieldValue = evaluationResult.value;
         if (fieldValue != null && !runtimeTypeMatch(fieldValue, fieldType)) {
           errorReporter.reportErrorForNode(
               CheckedModeCompileTimeErrorCode
@@ -549,6 +579,7 @@ class ConstantEvaluationEngine {
         new HashMap<String, DartObjectImpl>();
     List<ParameterElement> parameters = constructor.parameters;
     int parameterCount = parameters.length;
+
     for (int i = 0; i < parameterCount; i++) {
       ParameterElement parameter = parameters[i];
       ParameterElement baseParameter = parameter;
@@ -574,12 +605,23 @@ class ConstantEvaluationEngine {
         // The parameter is an optional positional parameter for which no value
         // was provided, so use the default value.
         validator.beforeGetParameterDefault(baseParameter);
-        EvaluationResultImpl evaluationResult = baseParameter.evaluationResult;
-        if (evaluationResult == null) {
-          // No default was provided, so the default value is null.
-          argumentValue = typeProvider.nullObject;
-        } else if (evaluationResult.value != null) {
-          argumentValue = evaluationResult.value;
+        if (strongMode && baseParameter is ConstVariableElement) {
+          var defaultValue =
+              (baseParameter as ConstVariableElement).constantInitializer;
+          if (defaultValue == null) {
+            argumentValue = typeProvider.nullObject;
+          } else {
+            argumentValue = defaultValue.accept(fieldInitVisitor);
+          }
+        } else {
+          EvaluationResultImpl evaluationResult =
+              baseParameter.evaluationResult;
+          if (evaluationResult == null) {
+            // No default was provided, so the default value is null.
+            argumentValue = typeProvider.nullObject;
+          } else if (evaluationResult.value != null) {
+            argumentValue = evaluationResult.value;
+          }
         }
       }
       if (argumentValue != null) {
@@ -677,6 +719,7 @@ class ConstantEvaluationEngine {
         if (superArguments == null) {
           superArguments = new NodeList<Expression>(null);
         }
+
         evaluateSuperConstructorCall(node, fieldMap, superConstructor,
             superArguments, initializerVisitor, errorReporter);
       }
@@ -688,7 +731,7 @@ class ConstantEvaluationEngine {
       AstNode node,
       HashMap<String, DartObjectImpl> fieldMap,
       ConstructorElement superConstructor,
-      NodeList<Expression> superArguments,
+      List<Expression> superArguments,
       ConstantVisitor initializerVisitor,
       ErrorReporter errorReporter) {
     if (superConstructor != null && superConstructor.isConst) {
@@ -1231,6 +1274,7 @@ class ConstantVisitor extends UnifyingAstVisitor<DartObjectImpl> {
       // problem - the error has already been reported.
       return null;
     }
+
     return evaluationEngine.evaluateConstructorCall(
         node, node.argumentList.arguments, constructor, this, _errorReporter);
   }
@@ -1274,9 +1318,9 @@ class ConstantVisitor extends UnifyingAstVisitor<DartObjectImpl> {
       return null;
     }
     DartType elementType = _typeProvider.dynamicType;
-    if (node.typeArguments != null &&
-        node.typeArguments.arguments.length == 1) {
-      DartType type = node.typeArguments.arguments[0].type;
+    NodeList<TypeName> typeArgs = node.typeArguments?.arguments;
+    if (typeArgs?.length == 1) {
+      DartType type = visitTypeName(typeArgs[0])?.toTypeValue();
       if (type != null) {
         elementType = type;
       }
@@ -1309,13 +1353,13 @@ class ConstantVisitor extends UnifyingAstVisitor<DartObjectImpl> {
     }
     DartType keyType = _typeProvider.dynamicType;
     DartType valueType = _typeProvider.dynamicType;
-    if (node.typeArguments != null &&
-        node.typeArguments.arguments.length == 2) {
-      DartType keyTypeCandidate = node.typeArguments.arguments[0].type;
+    NodeList<TypeName> typeArgs = node.typeArguments?.arguments;
+    if (typeArgs?.length == 2) {
+      DartType keyTypeCandidate = visitTypeName(typeArgs[0])?.toTypeValue();
       if (keyTypeCandidate != null) {
         keyType = keyTypeCandidate;
       }
-      DartType valueTypeCandidate = node.typeArguments.arguments[1].type;
+      DartType valueTypeCandidate = visitTypeName(typeArgs[1])?.toTypeValue();
       if (valueTypeCandidate != null) {
         valueType = valueTypeCandidate;
       }
@@ -1465,6 +1509,56 @@ class ConstantVisitor extends UnifyingAstVisitor<DartObjectImpl> {
         _typeProvider.symbolType, new SymbolState(buffer.toString()));
   }
 
+  @override
+  DartObjectImpl visitTypeName(TypeName node) {
+    DartType type = evaluateType(node.type);
+    if (type == null) {
+      return super.visitTypeName(node);
+    }
+    return typeConstant(type);
+  }
+
+  /**
+   * Given a [type], returns the constant value that contains that type value.
+   */
+  DartObjectImpl typeConstant(DartType type) {
+    return new DartObjectImpl(_typeProvider.typeType, new TypeState(type));
+  }
+
+  /**
+   * Given a [type] that may contain free type variables, evaluate them against
+   * the current lexical environment and return the substituted type.
+   */
+  DartType evaluateType(DartType type) {
+    if (type is TypeParameterType) {
+      if (!evaluationEngine.strongMode) {
+        return null;

[Paul Berry, 2016/07/29 12:22:46]

Nit: it would be nice to have a comment explaining why this is necessary, e.g.:

// Constants may only refer to type parameters in strong mode.

[Jennifer Messerly, 2016/07/29 16:04:50]

Done.

+      }
+
+      String name = type.name;
+      if (_lexicalEnvironment != null) {
+        return _lexicalEnvironment[name]?.toTypeValue() ?? type;
+      }
+      return type;
+    }
+    if (type is ParameterizedType) {
+      List<DartType> typeArguments;
+      for (int i = 0; i < type.typeArguments.length; i++) {
+        DartType ta = type.typeArguments[i];
+        DartType t = evaluateType(ta);
+        if (!identical(t, ta)) {
+          if (typeArguments == null) {
+            typeArguments = type.typeArguments.toList(growable: false);
+          }
+          typeArguments[i] = t;
+        }
+      }
+      if (typeArguments == null) return type;
+      return type.substitute2(typeArguments, type.typeArguments);
+    }
+    return type;
+  }
+
   /**
    * Create an error associated with the given [node]. The error will have the
    * given error [code].
@@ -1497,10 +1591,12 @@ class ConstantVisitor extends UnifyingAstVisitor<DartObjectImpl> {
         }
         return new DartObjectImpl(functionType, new FunctionState(function));
       }
-    } else if (variableElement is ClassElement ||
-        variableElement is FunctionTypeAliasElement ||
-        variableElement is DynamicElementImpl) {
-      return new DartObjectImpl(_typeProvider.typeType, new TypeState(element));
+    } else if (variableElement is TypeDefiningElement) {
+      if (evaluationEngine.strongMode ||
+          variableElement is! TypeParameterElement) {
+        return new DartObjectImpl(
+            _typeProvider.typeType, new TypeState(variableElement.type));
+      }
     }
     // TODO(brianwilkerson) Figure out which error to report.
     _error(node, null);