Add ast support for non-function type aliases

Change-Id: I5883ce6e80d451b52073f3770fbdf971e7dcf18c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/170692
Commit-Queue: Erik Ernst <eernst@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analyzer/lib/dart/analysis/features.dart

@@ -32,6 +32,10 @@ abstract class Feature {
   /// Feature information for the triple-shift operator.
   static final triple_shift = ExperimentalFeatures.triple_shift;
 
+  /// Feature information for non-function type aliases.
+  static final nonfunction_type_aliases =
+      ExperimentalFeatures.nonfunction_type_aliases;
+
   /// Feature information for variance.
   static final variance = ExperimentalFeatures.variance;
 

pkg/analyzer/lib/dart/ast/ast.dart

@@ -2933,12 +2933,18 @@ abstract class GenericTypeAlias implements TypeAlias {
   set equals(Token token);
 
   /// Return the type of function being defined by the alias.
+  ///
+  /// When the non-function type aliases feature is enabled and the denoted
+  /// type is not a [GenericFunctionType], return `null`.
   GenericFunctionType get functionType;
 
   /// Set the type of function being defined by the alias to the given
   /// [functionType].
   set functionType(GenericFunctionType functionType);
 
+  /// Return the type being defined by the alias.
+  TypeAnnotation get type;
+
   /// Return the type parameters for the function type, or `null` if the
   /// function type does not have any type parameters.
   TypeParameterList get typeParameters;

pkg/analyzer/lib/dart/ast/ast_factory.dart

@@ -511,7 +511,7 @@ abstract class AstFactory {
       SimpleIdentifier name,
       TypeParameterList typeParameters,
       Token equals,
-      GenericFunctionType functionType,
+      TypeAnnotation type,
       Token semicolon);
 
   /// Returns a newly created import show combinator.

pkg/analyzer/lib/src/dart/ast/ast.dart

@@ -5363,6 +5363,9 @@ class GenericFunctionTypeImpl extends TypeAnnotationImpl
 ///        metadata 'typedef' [SimpleIdentifier] [TypeParameterList]? =
 ///        [FunctionType] ';'
 class GenericTypeAliasImpl extends TypeAliasImpl implements GenericTypeAlias {
+  /// The type being defined by the alias.
+  TypeAnnotationImpl _type;
+
   /// The type parameters for the function type, or `null` if the function
   /// type does not have any type parameters.
   TypeParameterListImpl _typeParameters;
@@ -5370,9 +5373,6 @@ class GenericTypeAliasImpl extends TypeAliasImpl implements GenericTypeAlias {
   @override
   Token equals;
 
-  /// The type of function being defined by the alias.
-  GenericFunctionTypeImpl _functionType;
-
   /// Returns a newly created generic type alias. Either or both of the
   /// [comment] and [metadata] can be `null` if the variable list does not have
   /// the corresponding attribute. The [typeParameters] can be `null` if there
@@ -5384,11 +5384,11 @@ class GenericTypeAliasImpl extends TypeAliasImpl implements GenericTypeAlias {
       SimpleIdentifierImpl name,
       TypeParameterListImpl typeParameters,
       this.equals,
-      GenericFunctionTypeImpl functionType,
+      TypeAnnotationImpl type,
       Token semicolon)
       : super(comment, metadata, typedefToken, name, semicolon) {
     _typeParameters = _becomeParentOf(typeParameters);
-    _functionType = _becomeParentOf(functionType);
+    _type = _becomeParentOf(type);
   }
 
   @override
@@ -5398,19 +5398,30 @@ class GenericTypeAliasImpl extends TypeAliasImpl implements GenericTypeAlias {
     ..add(name)
     ..add(_typeParameters)
     ..add(equals)
-    ..add(_functionType);
+    ..add(_type);
 
   @override
   Element get declaredElement => name.staticElement;
 
+  /// The type of function being defined by the alias.
+  ///
+  /// If the non-function type aliases feature is enabled, a type alias may have
+  /// a [_type] which is not a [GenericFunctionTypeImpl].  In that case `null`
+  /// is returned.
   @override
-  GenericFunctionType get functionType => _functionType;
+  GenericFunctionType get functionType {
+    var t = _type;
+    return t is GenericFunctionTypeImpl ? t : null;
+  }
 
   @override
   set functionType(GenericFunctionType functionType) {
-    _functionType = _becomeParentOf(functionType as GenericFunctionTypeImpl);
+    _type = _becomeParentOf(functionType as TypeAnnotationImpl);
   }
 
+  @override
+  TypeAnnotation get type => _type;
+
   @override
   TypeParameterList get typeParameters => _typeParameters;
 
@@ -5429,7 +5440,7 @@ class GenericTypeAliasImpl extends TypeAliasImpl implements GenericTypeAlias {
     super.visitChildren(visitor);
     name?.accept(visitor);
     _typeParameters?.accept(visitor);
-    _functionType?.accept(visitor);
+    _type?.accept(visitor);
   }
 }
 

pkg/analyzer/lib/src/dart/ast/ast_factory.dart

@@ -575,10 +575,10 @@ class AstFactoryImpl extends AstFactory {
           SimpleIdentifier name,
           TypeParameterList typeParameters,
           Token equals,
-          GenericFunctionType functionType,
+          TypeAnnotation type,
           Token semicolon) =>
       GenericTypeAliasImpl(comment, metadata, typedefKeyword, name,
-          typeParameters, equals, functionType, semicolon);
+          typeParameters, equals, type, semicolon);
 
   @override
   HideCombinator hideCombinator(

pkg/analyzer/lib/src/fasta/ast_builder.dart

@@ -128,6 +128,9 @@ class AstBuilder extends StackListener {
   /// `true` if triple-shift behavior is enabled
   final bool enableTripleShift;
 
+  /// `true` if nonfunction-type-aliases behavior is enabled
+  final bool enableNonFunctionTypeAliases;
+
   /// `true` if variance behavior is enabled
   final bool enableVariance;
 
@@ -143,6 +146,8 @@ class AstBuilder extends StackListener {
         enableControlFlowCollections =
             _featureSet.isEnabled(Feature.control_flow_collections),
         enableTripleShift = _featureSet.isEnabled(Feature.triple_shift),
+        enableNonFunctionTypeAliases =
+            _featureSet.isEnabled(Feature.nonfunction_type_aliases),
         enableVariance = _featureSet.isEnabled(Feature.variance),
         uri = uri ?? fileUri;
 
@@ -1532,10 +1537,8 @@ class AstBuilder extends StackListener {
       SimpleIdentifier name = pop();
       List<Annotation> metadata = pop();
       Comment comment = _findComment(metadata, typedefKeyword);
-      if (type is! GenericFunctionType) {
-        // This error is also reported in the OutlineBuilder.
+      if (type is! GenericFunctionType && !enableNonFunctionTypeAliases) {
         handleRecoverableError(messageTypedefNotFunction, equals, equals);
-        type = null;
       }
       declarations.add(ast.genericTypeAlias(
           comment,
@@ -1544,7 +1547,7 @@ class AstBuilder extends StackListener {
           name,
           templateParameters,
           equals,
-          type as GenericFunctionType,
+          type,
           semicolon));
     }
   }
@@ -3042,8 +3045,11 @@ class AstBuilder extends StackListener {
 
       // Determine if this is a set or map based on type args and content
       final typeArgCount = typeArguments?.arguments?.length;
-      bool isSet =
-          typeArgCount == 1 ? true : typeArgCount != null ? false : null;
+      bool isSet = typeArgCount == 1
+          ? true
+          : typeArgCount != null
+              ? false
+              : null;
       isSet ??= hasSetEntry;
 
       // Build the set or map