[PATCH 2/4] libstdc++: Add a test for <version> FTM redefinitions

[Jonathan Wakely]

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?