Jonathan Wakely <jwakely@redhat.com> writes:

> On 05/04/23 01:09 +0200, Arsen Arsenović wrote:
>>This test detects redefinitions by compiling stdc++.h with
>>-Wsystem-headers.  Thanks Patrick Palka for the suggestion.
>>
>>libstdc++-v3/ChangeLog:
>>
>>	* testsuite/17_intro/versionconflict.cc: New test.
>>---
>> libstdc++-v3/testsuite/17_intro/versionconflict.cc | 6 ++++++
>> 1 file changed, 6 insertions(+)
>> create mode 100644 libstdc++-v3/testsuite/17_intro/versionconflict.cc
>>
>>diff --git a/libstdc++-v3/testsuite/17_intro/versionconflict.cc b/libstdc++-v3/testsuite/17_intro/versionconflict.cc
>>new file mode 100644
>>index 00000000000..4191c7a2b08
>>--- /dev/null
>>+++ b/libstdc++-v3/testsuite/17_intro/versionconflict.cc
>>@@ -0,0 +1,6 @@
>>+// { dg-do preprocess }
>>+// { dg-additional-options "-Wsystem-headers -Werror" }
>>+
>>+// Test for redefinitions of FTMs using bits/stdc++.h.
>>+#include <bits/stdc++.h>
>>+#include <version>
>
> I'm concerned that this will fail if libc headers have macro
> redefinition errors, or anything else that would usually be ignored.
>
> We could make it more robust by changing <version> like so:
>
> --- a/libstdc++-v3/include/std/version
> +++ b/libstdc++-v3/include/std/version
> @@ -30,7 +30,9 @@
>  #ifndef _GLIBCXX_VERSION_INCLUDED
>  #define _GLIBCXX_VERSION_INCLUDED
>  +#ifndef _GLIBCXX_TESTING_SYSHDR
>  #pragma GCC system_header
> +#endif
>    #include <bits/c++config.h>
>  Then the test could define that macro instead of using -Wsystem-headers.
>
> Could you see if that works?

Good idea.  Both the positive and negative cases work when implemented
like this: