[analyzer] Change return type of some TypeSystemImpl methods.

The following methods of `TypeSystemImpl` have their return type
changed from `DartType` to `TypeImpl`:

- `flatten`
- `greatestClosureOfSchema`
- `leastClosureOfSchema`
- `resolveToBound`

This is part of a larger arc of work to change the analyzer's use of
the shared code so that the type parameters it supplies are not part
of the analyzer public API. See
#59763.

Change-Id: I9cf82a644b944f18bae9435ba68c896d45723281
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/405062
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

pkg/analyzer/lib/src/dart/element/type_system.dart

@@ -400,16 +400,18 @@ class TypeSystemImpl implements TypeSystem {
   }
 
   @override
-  DartType flatten(DartType T) {
-    if (identical(T, UnknownInferredType.instance)) {
+  TypeImpl flatten(DartType T) {
+    // TODO(paulberry): remove this cast by making the parameter `T` covariant
+    // and changing its type to `TypeImpl`.
+    if (identical(T as TypeImpl, UnknownInferredType.instance)) {
       return T;
     }
 
     // if T is S? then flatten(T) = flatten(S)?
     var nullabilitySuffix = T.nullabilitySuffix;
     if (nullabilitySuffix != NullabilitySuffix.none) {
-      var S = (T as TypeImpl).withNullability(NullabilitySuffix.none);
-      return (flatten(S) as TypeImpl).withNullability(nullabilitySuffix);
+      var S = T.withNullability(NullabilitySuffix.none);
+      return flatten(S).withNullability(nullabilitySuffix);
     }
 
     // If T is X & S for some type variable X and type S then:
@@ -629,13 +631,15 @@ class TypeSystemImpl implements TypeSystem {
   ///
   /// Note that the greatest closure of a type schema is always a supertype of
   /// any type which matches the schema.
-  DartType greatestClosureOfSchema(DartType schema) {
+  TypeImpl greatestClosureOfSchema(DartType schema) {
+    // TODO(paulberry): remove this cast by making `ReplacementVisitor`
+    // implement `TypeVisitor<TypeImpl?>`.
     return TypeSchemaEliminationVisitor.run(
       topType: objectQuestion,
       bottomType: NeverTypeImpl.instance,
       isLeastClosure: false,
       schema: schema,
-    );
+    ) as TypeImpl;
   }
 
   @override
@@ -1413,13 +1417,15 @@ class TypeSystemImpl implements TypeSystem {
   ///
   /// Note that the least closure of a type schema is always a subtype of any
   /// type which matches the schema.
-  DartType leastClosureOfSchema(DartType schema) {
+  TypeImpl leastClosureOfSchema(DartType schema) {
+    // TODO(paulberry): remove this cast by making `ReplacementVisitor`
+    // implement `TypeVisitor<TypeImpl?>`.
     return TypeSchemaEliminationVisitor.run(
       topType: objectQuestion,
       bottomType: NeverTypeImpl.instance,
       isLeastClosure: true,
       schema: schema,
-    );
+    ) as TypeImpl;
   }
 
   @override
@@ -1717,7 +1723,10 @@ class TypeSystemImpl implements TypeSystem {
   }
 
   @override
-  DartType resolveToBound(DartType type) {
+  TypeImpl resolveToBound(DartType type) {
+    // TODO(paulberry): remove this cast by making the parameter `T` covariant
+    // and changing its type to `TypeImpl`.
+    type as TypeImpl;
     if (type is TypeParameterTypeImpl) {
       var promotedBound = type.promotedBound;
       if (promotedBound != null) {
@@ -1729,7 +1738,7 @@ class TypeSystemImpl implements TypeSystem {
         return objectQuestion;
       }
 
-      var resolved = resolveToBound(bound) as TypeImpl;
+      var resolved = resolveToBound(bound);
 
       var newNullabilitySuffix = uniteNullabilities(
         uniteNullabilities(

pkg/analyzer/lib/src/dart/resolver/comment_reference_resolver.dart

@@ -9,6 +9,7 @@ import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
+import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/type_provider.dart';
 import 'package:analyzer/src/dart/element/type_system.dart';
 import 'package:analyzer/src/dart/resolver/type_property_resolver.dart';
@@ -165,7 +166,7 @@ class CommentReferenceResolver {
         var extendedType = _typeSystem.resolveToBound(
           enclosingExtension.extendedType,
         );
-        if (extendedType is InterfaceType) {
+        if (extendedType is InterfaceTypeImpl) {
           enclosingType = extendedType;
         } else if (extendedType is FunctionType) {
           enclosingType = _typeProvider.functionType;

pkg/analyzer/lib/src/dart/resolver/type_property_resolver.dart

@@ -14,6 +14,7 @@ import 'package:analyzer/src/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/extensions.dart';
 import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
+import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/type_provider.dart';
 import 'package:analyzer/src/dart/element/type_system.dart';
 import 'package:analyzer/src/dart/resolver/extension_member_resolver.dart';
@@ -180,7 +181,7 @@ class TypePropertyResolver {
     } else {
       var receiverTypeResolved = _typeSystem.resolveToBound(receiverType);
 
-      if (receiverTypeResolved is InterfaceType) {
+      if (receiverTypeResolved is InterfaceTypeImpl) {
         _lookupInterfaceType(receiverTypeResolved);
         if (_hasGetterOrSetter) {
           return _toResult();
@@ -193,7 +194,7 @@ class TypePropertyResolver {
         }
       }
 
-      if (receiverTypeResolved is FunctionType &&
+      if (receiverTypeResolved is FunctionTypeImpl &&
           _name == FunctionElement.CALL_METHOD_NAME) {
         return ResolutionResult(
           needsGetterError: false,
@@ -209,7 +210,7 @@ class TypePropertyResolver {
         return _toResult();
       }
 
-      if (receiverTypeResolved is RecordType) {
+      if (receiverTypeResolved is RecordTypeImpl) {
         var field = receiverTypeResolved.fieldByName(name);
         if (field != null) {
           return ResolutionResult(

pkg/analyzer/lib/src/generated/resolver.dart

@@ -1213,7 +1213,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
     }
 
     var context = typeSystem.flatten(contextType);
-    if (context is! FunctionType || context.typeFormals.isNotEmpty) {
+    if (context is! FunctionTypeImpl || context.typeFormals.isNotEmpty) {
       return expression;
     }