[cfe] Handle UnknownType using defaultDartType

Change-Id: I4c3d805a4be6a6f95d08869325da077b654436d7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/114517
Reviewed-by: Dmitry Stefantsov <dmitryas@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

pkg/front_end/lib/src/fasta/kernel/verifier.dart

@@ -9,6 +9,7 @@ import 'package:kernel/ast.dart'
         AsExpression,
         Class,
         Component,
+        DartType,
         ExpressionStatement,
         Field,
         Let,
@@ -32,7 +33,7 @@ import '../fasta_codes.dart'
 
 import '../severity.dart' show Severity;
 
-import '../type_inference/type_schema.dart' show TypeSchemaVisitor, UnknownType;
+import '../type_inference/type_schema.dart' show UnknownType;
 
 import 'kernel_shadow_ast.dart' show SyntheticExpressionJudgment;
 
@@ -47,8 +48,7 @@ List<LocatedMessage> verifyComponent(Component component,
   return verifier.errors;
 }
 
-class FastaVerifyingVisitor extends VerifyingVisitor
-    implements TypeSchemaVisitor<void> {
+class FastaVerifyingVisitor extends VerifyingVisitor {
   final List<LocatedMessage> errors = <LocatedMessage>[];
 
   Uri fileUri;
@@ -174,9 +174,12 @@ class FastaVerifyingVisitor extends VerifyingVisitor
   }
 
   @override
-  visitUnknownType(UnknownType node) {
-    // Note: we can't pass [node] to [problem] because it's not a [TreeNode].
-    problem(null, "Unexpected appearance of the unknown type.");
+  defaultDartType(DartType node) {
+    if (node is UnknownType) {
+      // Note: we can't pass [node] to [problem] because it's not a [TreeNode].
+      problem(null, "Unexpected appearance of the unknown type.");
+    }
+    super.defaultDartType(node);
   }
 
   @override

pkg/front_end/lib/src/fasta/type_inference/type_schema.dart

@@ -32,7 +32,7 @@ String typeSchemaToString(DartType schema) {
 }
 
 /// Extension of [Printer] that represents the unknown type as `?`.
-class TypeSchemaPrinter extends Printer implements TypeSchemaVisitor<Null> {
+class TypeSchemaPrinter extends Printer {
   TypeSchemaPrinter(StringSink sink,
       {NameSystem syntheticNames,
       bool showExternal,
@@ -47,17 +47,11 @@ class TypeSchemaPrinter extends Printer implements TypeSchemaVisitor<Null> {
             annotator: annotator);
 
   @override
-  visitUnknownType(UnknownType node) {
+  defaultDartType(covariant UnknownType node) {
     writeWord('?');
   }
 }
 
-/// Extension of [DartTypeVisitor] which can visit [UnknownType].
-class TypeSchemaVisitor<R> extends DartTypeVisitor<R> {
-  /// Called when [UnknownType] is visited.
-  R visitUnknownType(UnknownType node) => defaultDartType(node);
-}
-
 /// The unknown type (denoted `?`) is an object which can appear anywhere that
 /// a type is expected.  It represents a component of a type which has not yet
 /// been fixed by inference.
@@ -78,16 +72,7 @@ class UnknownType extends DartType {
 
   @override
   R accept<R>(DartTypeVisitor<R> v) {
-    if (v is TypeSchemaVisitor<R>) {
-      return v.visitUnknownType(this);
-    } else {
-      // Note: in principle it seems like this should throw, since any visitor
-      // that operates on a type schema ought to inherit from TypeSchemaVisitor.
-      // However, that would make it impossible to use toString() on any type
-      // schema, since toString() uses the kernel's Printer visitor, which can't
-      // possibly inherit from TypeSchemaVisitor since it's inside kernel.
-      return v.defaultDartType(this);
-    }
+    return v.defaultDartType(this);
   }
 
   @override
@@ -99,9 +84,9 @@ class UnknownType extends DartType {
 }
 
 /// Visitor that computes [isKnown].
-class _IsKnownVisitor extends TypeSchemaVisitor<bool> {
+class _IsKnownVisitor extends DartTypeVisitor<bool> {
   @override
-  bool defaultDartType(DartType node) => true;
+  bool defaultDartType(DartType node) => node is! UnknownType;
 
   @override
   bool visitFunctionType(FunctionType node) {
@@ -130,7 +115,4 @@ class _IsKnownVisitor extends TypeSchemaVisitor<bool> {
     }
     return true;
   }
-
-  @override
-  bool visitUnknownType(UnknownType node) => false;
 }

pkg/front_end/lib/src/fasta/type_inference/type_schema_elimination.dart

@@ -3,11 +3,17 @@
 // BSD-style license that can be found in the LICENSE.md file.
 
 import 'package:kernel/ast.dart'
-    show DartType, DynamicType, FunctionType, InterfaceType, NamedType;
+    show
+        DartType,
+        DartTypeVisitor,
+        DynamicType,
+        FunctionType,
+        InterfaceType,
+        NamedType;
 
 import 'package:kernel/core_types.dart' show CoreTypes;
 
-import 'type_schema.dart' show TypeSchemaVisitor, UnknownType;
+import 'type_schema.dart' show UnknownType;
 
 /// Returns the greatest closure of the given type [schema] with respect to `?`.
 ///
@@ -46,7 +52,7 @@ DartType leastClosure(CoreTypes coreTypes, DartType schema) =>
 /// Each visitor method returns `null` if there are no `?`s contained in the
 /// type, otherwise it returns the result of substituting `?` with `Null` or
 /// `Object`, as appropriate.
-class _TypeSchemaEliminationVisitor extends TypeSchemaVisitor<DartType> {
+class _TypeSchemaEliminationVisitor extends DartTypeVisitor<DartType> {
   final DartType nullType;
 
   bool isLeastClosure;
@@ -115,8 +121,12 @@ class _TypeSchemaEliminationVisitor extends TypeSchemaVisitor<DartType> {
   }
 
   @override
-  DartType visitUnknownType(UnknownType node) =>
-      isLeastClosure ? nullType : const DynamicType();
+  DartType defaultDartType(DartType node) {
+    if (node is UnknownType) {
+      return isLeastClosure ? nullType : const DynamicType();
+    }
+    return null;
+  }
 
   /// Runs an instance of the visitor on the given [schema] and returns the
   /// resulting type.  If the schema contains no instances of `?`, the original

pkg/front_end/test/fasta/type_inference/type_schema_test.dart

@@ -117,7 +117,7 @@ class _OrdinaryVisitor<R> extends Visitor<R> {
   }
 }
 
-class _TypeSchemaVisitor<R> extends Visitor<R> implements TypeSchemaVisitor<R> {
+class _TypeSchemaVisitor<R> extends Visitor<R> {
   final _UnaryFunction<DartType, R> _defaultDartType;
   final _UnaryFunction<UnknownType, R> _visitUnknownType;
 
@@ -129,19 +129,12 @@ class _TypeSchemaVisitor<R> extends Visitor<R> implements TypeSchemaVisitor<R> {
 
   @override
   R defaultDartType(DartType node) {
-    if (_defaultDartType != null) {
+    if (node is UnknownType && _visitUnknownType != null) {
+      return _visitUnknownType(node);
+    } else if (_defaultDartType != null) {
       return _defaultDartType(node);
     } else {
       return super.defaultDartType(node);
     }
   }
-
-  @override
-  R visitUnknownType(UnknownType node) {
-    if (_visitUnknownType != null) {
-      return _visitUnknownType(node);
-    } else {
-      return defaultDartType(node);
-    }
-  }
 }