Check contravariance of property gets that resolve to fields.

Fixes #32501

Change-Id: Ic3c5aca1d12b73e40e63c6cdd8304b95f54e5497
Reviewed-on: https://dart-review.googlesource.com/46002
Reviewed-by: Dmitry Stefantsov <dmitryas@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

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

@@ -875,9 +875,12 @@ abstract class TypeInferrerImpl extends TypeInferrer {
     }
     desugaredGet?.dispatchCategory = callKind;
     bool checkReturn = false;
-    if (callKind == DispatchCategory.interface &&
-        interfaceMember is Procedure) {
+    if (callKind == DispatchCategory.interface) {
+      if (interfaceMember is Procedure) {
         checkReturn = interfaceMember.isGenericContravariant;
+      } else if (interfaceMember is Field) {
+        checkReturn = interfaceMember.isGenericContravariant;
+      }
     }
     var replacedExpression = desugaredGet ?? expression;
     if (checkReturn) {

pkg/front_end/testcases/runtime_checks/contravariant_field.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2018, 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.
+
+/*@testedFeatures=checks*/
+library test;
+
+typedef void F<T>(T x);
+
+class C<T> {
+  F<T> /*@genericContravariant=true*/ y;
+  void f() {
+    var x = this. /*@callKind=this*/ y;
+  }
+}
+
+void g(C<num> c) {
+  var x = c. /*@checkReturn=(num) -> void*/ y;
+}
+
+void main() {}

pkg/front_end/testcases/runtime_checks/contravariant_field.dart.direct.expect

@@ -0,0 +1,18 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+typedef F<T extends core::Object> = (T) → void;
+class C<T extends core::Object> extends core::Object {
+  field (self::C::T) → void y = null;
+  synthetic constructor •() → void
+    : super core::Object::•()
+    ;
+  method f() → void {
+    dynamic x = this.{self::C::y};
+  }
+}
+static method g(self::C<core::num> c) → void {
+  dynamic x = c.y;
+}
+static method main() → void {}

pkg/front_end/testcases/runtime_checks/contravariant_field.dart.outline.expect

@@ -0,0 +1,16 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+typedef F<T extends core::Object> = (T) → void;
+class C<T extends core::Object> extends core::Object {
+  field (self::C::T) → void y;
+  synthetic constructor •() → void
+    ;
+  method f() → void
+    ;
+}
+static method g(self::C<core::num> c) → void
+  ;
+static method main() → void
+  ;

pkg/front_end/testcases/runtime_checks/contravariant_field.dart.strong.expect

@@ -0,0 +1,18 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+typedef F<T extends core::Object> = (T) → void;
+class C<T extends core::Object> extends core::Object {
+  generic-contravariant field (self::C::T) → void y = null;
+  synthetic constructor •() → void
+    : super core::Object::•()
+    ;
+  method f() → void {
+    (self::C::T) → void x = this.{self::C::y};
+  }
+}
+static method g(self::C<core::num> c) → void {
+  (core::num) → void x = c.{self::C::y} as{TypeError} (core::num) → void;
+}
+static method main() → void {}