Use a special context for serializing generic function types.

This is necessary to ensure that type parameters that refer to the
enclosing context get serialized correctly.

Change-Id: I1e95cc4e83be76bf003faa037eff80728c1fb748
Reviewed-on: https://dart-review.googlesource.com/c/79145
Auto-Submit: Paul Berry <paulberry@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

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

@@ -7676,7 +7676,10 @@ class TypeParameterElementImpl extends ElementImpl
 
 /// Mixin representing an element which can have type parameters.
 abstract class TypeParameterizedElementMixin
-    implements TypeParameterizedElement, ElementImpl {
+    implements
+        TypeParameterizedElement,
+        ElementImpl,
+        TypeParameterSerializationContext {
   /// A cached list containing the type parameters declared by this element
   /// directly, or `null` if the elements have not been created yet. This does
   /// not include type parameters that are declared by any enclosing elements.
@@ -7727,10 +7730,7 @@ abstract class TypeParameterizedElementMixin
   /// TODO(scheglov) make private after switching linker to Impl
   List<UnlinkedTypeParam> get unlinkedTypeParams;
 
-  /// Return the given [typeParameter]'s de Bruijn index in this context, or
-  /// `null` if it's not in scope.
-  ///
-  /// If an [offset] is provided, then it is added to the computed index.
+  @override
   int computeDeBruijnIndex(TypeParameterElement typeParameter,
       {int offset = 0}) {
     if (typeParameter.enclosingElement == this) {
@@ -7761,6 +7761,20 @@ abstract class TypeParameterizedElementMixin
   }
 }
 
+/// Interface used by linker serialization methods to convert type parameter
+/// references into De Bruijn indices.
+abstract class TypeParameterSerializationContext {
+  /// Return an object representing the location of this element in the element
+  /// model. The object can be used to locate this element at a later time.
+  ElementLocation get location;
+
+  /// Return the given [typeParameter]'s de Bruijn index in this context, or
+  /// `null` if it's not in scope.
+  ///
+  /// If an [offset] is provided, then it is added to the computed index.
+  int computeDeBruijnIndex(TypeParameterElement typeParameter, {int offset: 0});
+}
+
 /// Container with information about explicit top-level property accessors and
 /// corresponding implicit top-level variables.
 class UnitExplicitTopLevelAccessors {

pkg/analyzer/lib/src/summary/link.dart

@@ -181,7 +181,7 @@ List<EntityRef> _collectTypedefRhsTypes(UnlinkedTypedef unlinkedTypedef) {
 EntityRefBuilder _createLinkedType(
     DartType type,
     CompilationUnitElementInBuildUnit compilationUnit,
-    TypeParameterizedElementMixin typeParameterContext,
+    TypeParameterSerializationContext typeParameterContext,
     {int slot}) {
   EntityRefBuilder result = new EntityRefBuilder(slot: slot);
   if (type is InterfaceType) {
@@ -247,7 +247,8 @@ EntityRefBuilder _createLinkedType(
     }
     if (element is GenericFunctionTypeElementImpl) {
       // Function types are their own type parameter context
-      typeParameterContext = element;
+      typeParameterContext =
+          new InlineFunctionTypeParameterContext(element, typeParameterContext);
       result.entityKind = EntityRefKind.genericFunctionType;
       result.syntheticReturnType = _createLinkedType(
           type.returnType, compilationUnit, typeParameterContext);
@@ -309,7 +310,7 @@ void _relink(
 UnlinkedParamBuilder _serializeSyntheticParam(
     ParameterElement parameter,
     CompilationUnitElementInBuildUnit compilationUnit,
-    TypeParameterizedElementMixin typeParameterContext) {
+    TypeParameterSerializationContext typeParameterContext) {
   UnlinkedParamBuilder b = new UnlinkedParamBuilder();
   b.name = parameter.name;
   if (parameter.isNotOptional) {
@@ -343,7 +344,7 @@ UnlinkedParamBuilder _serializeSyntheticParam(
 UnlinkedTypeParamBuilder _serializeSyntheticTypeParameter(
     TypeParameterElement typeParameter,
     CompilationUnitElementInBuildUnit compilationUnit,
-    TypeParameterizedElementMixin typeParameterContext) {
+    TypeParameterSerializationContext typeParameterContext) {
   TypeParameterElementImpl impl = typeParameter as TypeParameterElementImpl;
   EntityRefBuilder boundBuilder = typeParameter.bound != null
       ? _createLinkedType(
@@ -387,7 +388,7 @@ void _storeTypeArguments(
     List<DartType> typeArguments,
     EntityRefBuilder encodedType,
     CompilationUnitElementInBuildUnit compilationUnit,
-    TypeParameterizedElementMixin typeParameterContext) {
+    TypeParameterSerializationContext typeParameterContext) {
   int count = typeArguments.length;
   List<EntityRefBuilder> encodedTypeArguments =
       new List<EntityRefBuilder>(count);
@@ -1645,7 +1646,7 @@ class CompilationUnitElementInBuildUnit extends CompilationUnitElementForLink {
   /// Store the given [linkedType] in the given [slot] of the this compilation
   /// unit's linked type list.
   void _storeLinkedType(int slot, DartType linkedType,
-      TypeParameterizedElementMixin typeParameterContext) {
+      TypeParameterSerializationContext typeParameterContext) {
     if (slot != 0) {
       if (linkedType != null && !linkedType.isDynamic) {
         _linkedUnit.types.add(_createLinkedType(
@@ -3364,6 +3365,34 @@ class GenericTypeAliasElementForLink extends Object
   String toString() => '$enclosingElement.$name';
 }
 
+/// Context for serializing a possibly generic function type that is used in
+/// another context.
+class InlineFunctionTypeParameterContext
+    implements TypeParameterSerializationContext {
+  final GenericFunctionTypeElementImpl _functionTypeElement;
+
+  final TypeParameterSerializationContext _usageContext;
+
+  InlineFunctionTypeParameterContext(
+      this._functionTypeElement, this._usageContext);
+
+  @override
+  ElementLocation get location =>
+      throw new UnimplementedError('TODO(paulberry)');
+
+  @override
+  int computeDeBruijnIndex(TypeParameterElement typeParameter,
+      {int offset: 0}) {
+    var typeFormals = _functionTypeElement.typeParameters;
+    var numTypeFormals = typeFormals.length;
+    for (int i = 0; i < numTypeFormals; i++) {
+      if (typeFormals[i] == typeParameter) return i + offset + 1;
+    }
+    return _usageContext.computeDeBruijnIndex(typeParameter,
+        offset: offset + numTypeFormals);
+  }
+}
+
 /// Specialization of [DependencyWalker] for linking library cycles.
 class LibraryCycleDependencyWalker extends DependencyWalker<LibraryCycleNode> {
   @override

pkg/analyzer/test/src/summary/linker_test.dart

@@ -443,7 +443,6 @@ class C extends A<int> {
     expect(fType.parameters[0].type.toString(), 'int');
   }
 
-  @failingTest
   void test_inferredType_parameter_genericFunctionType_asTypeArgument() {
     var bundle = createPackageBundle('''
 class A<T> {