[Bug c++/114436] New: #pragma GCC system_header vs. _Pragma("GCC system_header")

[Bug c++/114436] New: #pragma GCC system_header vs. _Pragma("GCC system_header")

[finke at cognitec dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114436

            Bug ID: 114436
           Summary: #pragma GCC system_header vs. _Pragma("GCC
                    system_header")
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: finke at cognitec dot com
  Target Milestone: ---

Created attachment 57784
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57784&action=edit
code snippet

When using the _Pragma operator instead of the #pragma directive for "GCC
system_header", a different behavior can be observed:

Warnings in included header files are not being ignored as it is the case with
the #pragma directive.

The attached code snippet does emit an error when compiled with 
"g++ -Werror=unused-parameter pragma.cc"

The expectation would be, that it compiles without error (clang is compiling it
without error).

gcc versions tested: 4.8.5 & 13.2.1

Output from compiler:
In file included from pragma.h:10:0,
                 from pragma.cc:1:
third_party.h:4:13: error: unused parameter 'force_unused_warning'
[-Werror=unused-parameter]
 inline void foo( int force_unused_warning) {
             ^
cc1plus: some warnings being treated as errors

[Bug preprocessor/114436] #pragma GCC system_header vs. _Pragma("GCC system_header")

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114436

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=114423

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Maybe this is related to how _Pragma is treated in general.

[Bug preprocessor/114436] #pragma GCC system_header vs. _Pragma("GCC system_header")

[lhyatt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114436

Lewis Hyatt <lhyatt at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-03-22
             Status|UNCONFIRMED                 |NEW
                 CC|                            |lhyatt at gcc dot gnu.org

--- Comment #2 from Lewis Hyatt <lhyatt at gcc dot gnu.org> ---
This should fix it correctly, will test it sometime.

diff --git a/libcpp/directives.cc b/libcpp/directives.cc
index 479f8c716e8..36cc762e704 100644
--- a/libcpp/directives.cc
+++ b/libcpp/directives.cc
@@ -1986,7 +1986,9 @@ destringize_and_run (cpp_reader *pfile, const cpp_string
*in,

   /* Finish inlining run_directive.  */
   pfile->buffer->file = NULL;
+  const auto new_sysp = pfile->buffer->sysp;
   _cpp_pop_buffer (pfile);
+  pfile->buffer->sysp = new_sysp;

   /* Reset the old macro state before ...  */
   XDELETE (pfile->context);

[Bug preprocessor/114436] #pragma GCC system_header vs. _Pragma("GCC system_header")

[lhyatt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114436

Lewis Hyatt <lhyatt at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
                URL|                            |https://gcc.gnu.org/piperma
                   |                            |il/gcc-patches/2024-March/6
                   |                            |48297.html

--- Comment #3 from Lewis Hyatt <lhyatt at gcc dot gnu.org> ---
Slight variation of the above submitted for review at
https://gcc.gnu.org/pipermail/gcc-patches/2024-March/648297.html