[model] Handle local function instantiations in type checks

Closes #61370

Change-Id: I6007bafaf7058bf1b2d5f7ec28f1413bc5a4e694
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/447700
Reviewed-by: Erik Ernst <[email protected]>
Reviewed-by: Paul Berry <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Chloe Stefantsova <[email protected]>

Author: chloestefantsova

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

@@ -957,18 +957,15 @@ extension on Element {
   /// `null` is returned. For [PropertyAccessorElement], the return value is
   /// returned. For all other elements, their `type` property is returned.
   DartType? get referenceType {
-    if (this is ConstructorElement) {
-      return (this as ConstructorElement).type;
-    } else if (this is TopLevelFunctionElement) {
-      return (this as TopLevelFunctionElement).type;
-    } else if (this is PropertyAccessorElement) {
-      return (this as PropertyAccessorElement).returnType;
-    } else if (this is MethodElement) {
-      return (this as MethodElement).type;
-    } else if (this is VariableElement) {
-      return (this as VariableElement).type;
-    } else {
-      return null;
-    }
+    var self = this;
+    return switch (self) {
+      ConstructorElement() => self.type,
+      TopLevelFunctionElement() => self.type,
+      LocalFunctionElement() => self.type,
+      PropertyAccessorElement() => self.returnType,
+      MethodElement() => self.type,
+      VariableElement() => self.type,
+      _ => null,
+    };
   }
 }

tests/language/inference/issue_61370_2_error_test.dart

@@ -0,0 +1,44 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+typedef F<X> = X Function(X);
+
+extension<X> on X {
+  X m<Y extends F<X>>() => this;
+}
+
+void test1() {
+  g() sync* {
+    yield 1;
+    yield null;
+  }
+
+  g.m<F<Iterable<int?> Function()>>();
+  g.m<F<Iterable<int?> Function()>>;
+  g.m<F<Iterable<int> Function()>>();
+  //^
+  // [cfe] Type argument 'Iterable<int> Function() Function(Iterable<int> Function())' doesn't conform to the bound 'X Function(X)' of the type variable 'Y' on 'm'.
+  //  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  // [analyzer] COMPILE_TIME_ERROR.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS
+  g.m<F<Iterable<int> Function()>>;
+  // ^
+  // [cfe] Type argument 'Iterable<int> Function() Function(Iterable<int> Function())' doesn't conform to the bound 'Iterable<int?> Function() Function(Iterable<int?> Function())' of the type variable 'Y' on 'Iterable<int?> Function() Function<Y extends Iterable<int?> Function() Function(Iterable<int?> Function())>()'.
+  //  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  // [analyzer] COMPILE_TIME_ERROR.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS
+}
+
+void test2(Iterable<int?> h()) {
+  h.m<F<Iterable<int?> Function()>>();
+  h.m<F<Iterable<int?> Function()>>;
+  h.m<F<Iterable<int> Function()>>();
+  //^
+  // [cfe] Type argument 'Iterable<int> Function() Function(Iterable<int> Function())' doesn't conform to the bound 'X Function(X)' of the type variable 'Y' on 'm'.
+  //  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  // [analyzer] COMPILE_TIME_ERROR.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS
+  h.m<F<Iterable<int> Function()>>;
+  // ^
+  // [cfe] Type argument 'Iterable<int> Function() Function(Iterable<int> Function())' doesn't conform to the bound 'Iterable<int?> Function() Function(Iterable<int?> Function())' of the type variable 'Y' on 'Iterable<int?> Function() Function<Y extends Iterable<int?> Function() Function(Iterable<int?> Function())>()'.
+  //  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  // [analyzer] COMPILE_TIME_ERROR.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS
+}

tests/language/inference/issue_61370_error_test.dart

@@ -0,0 +1,44 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+typedef F<X> = X Function(X);
+
+extension<X> on X {
+  X m<Y extends F<X>>() => this;
+}
+
+void test1() {
+  g() {
+    if (2 > 1) return 1;
+    return null;
+  }
+
+  g.m<F<int? Function()>>();
+  g.m<F<int? Function()>>;
+  g.m<F<int Function()>>();
+  //^
+  // [cfe] Type argument 'int Function() Function(int Function())' doesn't conform to the bound 'X Function(X)' of the type variable 'Y' on 'm'.
+  //  ^^^^^^^^^^^^^^^^^
+  // [analyzer] COMPILE_TIME_ERROR.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS
+  g.m<F<int Function()>>;
+  // ^
+  // [cfe] Type argument 'int Function() Function(int Function())' doesn't conform to the bound 'int? Function() Function(int? Function())' of the type variable 'Y' on 'int? Function() Function<Y extends int? Function() Function(int? Function())>()'.
+  //  ^^^^^^^^^^^^^^^^^
+  // [analyzer] COMPILE_TIME_ERROR.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS
+}
+
+void test2(int? h()) {
+  h.m<F<int? Function()>>();
+  h.m<F<int? Function()>>;
+  h.m<F<int Function()>>();
+  //^
+  // [cfe] Type argument 'int Function() Function(int Function())' doesn't conform to the bound 'X Function(X)' of the type variable 'Y' on 'm'.
+  //  ^^^^^^^^^^^^^^^^^
+  // [analyzer] COMPILE_TIME_ERROR.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS
+  h.m<F<int Function()>>;
+  // ^
+  // [cfe] Type argument 'int Function() Function(int Function())' doesn't conform to the bound 'int? Function() Function(int? Function())' of the type variable 'Y' on 'int? Function() Function<Y extends int? Function() Function(int? Function())>()'.
+  //  ^^^^^^^^^^^^^^^^^
+  // [analyzer] COMPILE_TIME_ERROR.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS
+}