Test for C++20 p0858 - ConstexprIterator requirements.

[Jonathan Wakely]

On 01/06/19 15:40 -0400, Ed Smith-Rowland via libstdc++ wrote:
>On 6/1/19 2:42 PM, Ville Voutilainen wrote:
>>On Sat, 1 Jun 2019 at 21:09, Ed Smith-Rowland <3dw4rd@verizon.net> wrote:
>>>On 5/31/19 6:29 PM, Ville Voutilainen wrote:
>>>>On Sat, 1 Jun 2019 at 01:24, Ed Smith-Rowland via libstdc++
>>>><libstdc++@gcc.gnu.org> wrote:
>>>>>Greetings,
>>>>>
>>>>>Iterators for <array> and <string_view> are usabe in a constexpr context
>>>>>since C++2017.
>>>>>
>>>>>This just adds a compile test to make sure and check a box for C++20
>>>>>p0858 - ConstexprIterator requirements.
>>>>Those tests don't use the iterators in a constexpr context. To do
>>>>that, maybe do those std::copy operations
>>>>in a constexpr function and then initialize a constexpr variable with
>>>>the result of a call to that function?
>>>Thanks Ville,
>>>
>>>I had completely forgotten to make these test functions constexpr - FIXED.
>>.but that doesn't enforce a constexpr context. If you add another
>>function that calls these functions
>>and initializes a constexpr variable, then we have the enforcement I
>>seek. Such as
>>
>>void test2()
>>{
>>     constexpr char x = test();
>>}
>>
>Ok, third time's a charm.
>
>I was brain dead about the constexpr patch.?? I'm now setting a 
>constexpr variable from test() in a caller.
>
>But static_assert is a constexpr context no?
>
>Ed
>
>

>2019-06-03  Edward Smith-Rowland  <3dw4rd@verizon.net>
>
>	Test for C++20 p0858 - ConstexprIterator requirements.
>	* testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc:
>	New test.
>	* testsuite/23_containers/array/requirements/constexpr_iter.cc:
>	New test.
>

>Index: testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc
>===================================================================
>--- testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc	(nonexistent)
>+++ testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc	(working copy)
>@@ -0,0 +1,43 @@
>+// { dg-do compile { target c++2a } }

Please check the testsuite/libstdc++.log or testsuite/libstdc++.sum
files for the new tests. I expect they are both UNSUPPORTED.

That's because you've given a target c++2a which means they won't be
run unless a suitable -std option is given. And you haven't given one.

You need to add { dg-options "-std=gnu++2a" } before the dg-do line.

Also if the tests are restricted to C++2a then there's no point having
the #if __cplusplus > 201703L check, because that will never be false.