[libc++] Refactor std::function tests

[ldionne]

Summary

Some of those .compile.fail.cpp tests had become incorrect and they
were not testing anything. In general, .compile.fail.cpp tests are
bad because they make it way too easy to write garbage tests. Indeed,
the test could fail to compile due to any reason whatsoever (even a
typo) and it would appear to work correctly.

[philnik]

Could you mention in the commit message that you are refactoring the .fail.cpp tests specifically?

[ldionne]

In D138731#3951541, @philnik wrote:

Could you mention in the commit message that you are refactoring the .fail.cpp tests specifically?

Will do upon committing.

[ldionne]

CI issues were flake, shipping.

libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/derive_from.verify.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03
-// XFAIL: c++11, c++14
+// UNSUPPORTED: c++03, c++11, c++14
 
 // <functional>
+//
+// Make sure we can't initialize a std::function using an allocator (http://wg21.link/p0302r1).
+// These constructors were removed in C++17.
 
 #include <functional>
-#include <type_traits>
-
-#include "test_macros.h"
+#include <memory>
 
 struct S : public std::function<void()> { using function::function; };
 
-int main(int, char**) {
-   S f1( [](){} );
-   S f2(std::allocator_arg, std::allocator<int>{}, f1);
-
-  return 0;
+void f() {
+  S f2(std::allocator_arg, std::allocator<int>{}, f1); // expected-error {{no matching constructor for initialization of 'S'}}
 }

libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.inv/invoke.verify.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: c++03
+
 // <functional>
 
 // class function<R(ArgTypes...)>
 
 // R operator()(ArgTypes... args) const
 
 #include <functional>
 #include <cassert>
 
-// member data pointer:  cv qualifiers should transfer from argument to return type
+// member data pointer: cv qualifiers should transfer from argument to return type
 
-struct A_int_1
-{
-    A_int_1() : data_(5) {}
-
-    int data_;
-};
-
-void
-test_int_1()
-{
-    // member data pointer
-    {
-        int A_int_1::*fp = &A_int_1::data_;
-        A_int_1 a;
-        std::function<int& (const A_int_1*)> r2(fp);
-        const A_int_1* ap = &a;
-        assert(r2(ap) == 6);
-        r2(ap) = 7;
-        assert(r2(ap) == 7);
-    }
-}
-
-int main(int, char**)
-{
-    test_int_1();
+struct Foo { int data; };
 
-  return 0;
+void f() {
+    int Foo::*fp = &Foo::data;
+    std::function<int& (const Foo*)> r2(fp); // expected-error {{no matching constructor for initialization of}}
 }