Fixes #996: more tests added.

Author: iarkh

LanguageFeatures/Generic-functions-as-type-args/typedef3_A01_t06.dart

@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2021, 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.
+ */
+/**
+ * @assertion Allow generic function types as type arguments and bounds
+ *
+ * The language disallows generic function types as type arguments and bounds.
+ *
+ *  late List<T Function<T>(T)> idFunctions; // INVALID.
+ *  var callback = [foo<T>(T value) => value]; // Inferred as above, then invalid.
+ *  late S Function<S extends T Function<T>(T)>(S) f; // INVALID.
+ *
+ * We remove that restriction, so a type argument and a bound can be a generic
+ * function type.
+ *
+ * This requires no new syntax, and in some cases only the removal of a single
+ * check. There might be some platforms where the implementation currently
+ * assumes that generic function types cannot occur as the value of type
+ * variables (an proof-of-concept attempt hit an assert in the VM). Such
+ * assumptions will need to be flushed out with tests and fixed.
+ *
+ * Because we already infer List<T Function<T>(T)> in the code above, this
+ * change will not affect type inference, it will just make the inferred type
+ * not be an error afterwards.
+ *
+ * We do not expect the removal of this restriction to affect the feasibility of
+ * type inference. After all, it's already possible to have a generic function
+ * type occurring covariantly in a type argument, like List<T Function<T>(T)
+ * Function()>.
+ * @description Checks that generic function can be a non-function typedef type
+ * argument and bound: test extends clause in the typedef declaration
+ * statically.
+ * @Issue 45065
+ * @author [email protected]
+ */
+// SharedOptions=--enable-experiment=generic-metadata
+
+typedef exp1 = T Function<T>(T);
+typedef exp2 = void Function<T>();
+typedef exp3 = T Function<T>();
+typedef exp4 = void Function<T>(T);
+
+class C<T> {}
+
+typedef C1<X extends exp4> = C<X>;
+
+test1() {
+  C1 c = C1<int>();
+//       ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  C1 c1 = C1<exp1>();
+
+  C1 c2 = C1<exp2>();
+//        ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  C1 c3 = C1<exp3>();
+//        ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  C1 c4 = C1<exp4>();
+}
+
+test2() {
+  C1<int>();
+//   ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  C1<exp1>();
+
+  C1<exp2>();
+//   ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  C1<exp3>();
+//   ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  C1<exp4>();
+}
+
+main() {}