Create test for language issue 1182

Add language/extension_methods/static_extension_resolution_7_test.dart,
testing that the inference of a type argument to an extension method
invocation treats bounded type variables and promoted type variables
as specified, and as discussed in language issue #1182.

Change-Id: I99f358eb82dcce235edb091bc2bae172c2725d39
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/165022
Commit-Queue: Erik Ernst <[email protected]>
Reviewed-by: Lasse R.H. Nielsen <[email protected]>

tests/language/extension_methods/static_extension_resolution_7_test.dart

@@ -0,0 +1,65 @@
+// Copyright (c) 2020, 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.
+
+import "package:expect/expect.dart";
+
+// Tests the resolution of a bare type variable with bounded or promoted type.
+
+extension E<T> on T {
+  T Function(T) get f => (_) => this;
+}
+
+class A<S extends num> {
+  void testBoundedTypeVariable(S s) {
+    // Check that `num` has no `f` so E is applicable, then bind `T` to `S`.
+    S Function(S) f = s.f;
+  }
+
+  void testPromotedTypeVariable(S s) {
+    if (s is int) {
+      // Check that `int` has no `f`, erase `S & int` to `S`, bind `T` to `S`.
+      S Function(S) f = s.f;
+    }
+  }
+}
+
+class B<S extends dynamic> {
+  void testBoundedTypeVariable(S s) {
+    // `dynamic` considered to have `f`, E not applicable, dynamic invocation.
+    Expect.throws(() => s.f);
+  }
+
+  void testPromotedType(S s) {
+    if (s is int) {
+      // Check that `int` has no `f`, bind `T` to `int`.
+      int Function(int) f = s.f;
+    }
+  }
+}
+
+class C<S> {
+  void testBoundedTypeVariable(S s) {
+    // Check that `Object?` has no `f` so E is applicable, then bind `T` to `S`.
+    S Function(S) f = s.f;
+  }
+
+  void testPromotedType(S s) {
+    if (s is int) {
+      // Check that `int` has no `f`, bind `T` to `S`.
+      S Function(S) f = s.f;
+    }
+  }
+}
+
+void main() {
+  A<int>()
+    ..testBoundedTypeVariable(1)
+    ..testPromotedTypeVariable(2);
+  B<int>()
+    ..testBoundedTypeVariable(1)
+    ..testPromotedType(2);
+  C<int>()
+    ..testBoundedTypeVariable(1)
+    ..testPromotedType(2);
+}