[Bug c++/89808] New: Disable "#pragma once in main file"

[s_gcc_bugzilla at binarez dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89808

Bug ID: 89808
   Summary: Disable "#pragma once in main file"
   Product: gcc
   Version: 7.3.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: s_gcc_bugzilla at binarez dot com
  Target Milestone: ---

I am building an environnement to execute c++ code and I do need to use #pragma
once in my main cpp source code (and all cpp files actually). When I compile, I
get the "#pragma once in main file" warning.

The only way to turn this warning off is to disable all warnings with the -w
option. I want to only disable this specific warning and keep all the other
ones. gcc needs something like clang's -Wno-pragma-once-outside-header option.

I do appreciate that this warning is actually useful but there are corner cases
where this warning must be disabled.

[Bug preprocessor/89808] An option to disable warning "#pragma once in main file"

[s_gcc_bugzilla at binarez dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89808

--- Comment #3 from sduguay  ---
(In reply to Richard Biener from comment #1)
> Testcase:
> 
> #pragma once
> int main() {}
> 
> > g++ t.C -S
> t.C:1:9: warning: #pragma once in main file
>  #pragma once
>  ^~~~
> 
> 
> you could work around this by wrapping the pragma in a preprocessor
> conditional

Hi, thanks for adding a minimal test case. I tried:

#if 1
#pragma once
#endif

but I'm still getting the warning.

[Bug preprocessor/89808] An option to disable warning "#pragma once in main file"

[s_gcc_bugzilla at binarez dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89808

--- Comment #4 from sduguay  ---
(In reply to Jakub Jelinek from comment #2)
> You haven't explained why do you need to use #pragma once in the main cpp
> source file, are you sometimes including it as a header and other times
> compiling it as the TU itself?  Not to mention that it is best not to use
> #pragma once at all anywhere.

Yes, in the system I'm working on, there is no "main file", all C++ (xcpp files
actually) are small C++ programs that I link with a generated main file. xcpp
programs can use other programs (xcpp files) or libs (xhpp files).

This is all working pretty well right now, except for that #pragma once
warning. It's still under pretty heavy development.

You can try it @ https://github.com/binarez/xcpp


Thanks

[Bug preprocessor/89808] An option to disable warning "#pragma once in main file"

[s_gcc_bugzilla at binarez dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89808

--- Comment #8 from sduguay  ---
(In reply to Jonathan Wakely from comment #6)
> In any case, I agree with confirming this as a bug: all warnings should be
> controllable by a -Wxxx option.
> 
> Adding such an option is quite easy, and a good first contribution to GCC.
> For an example of adding a new option see https://gcc.gnu.org/r192968

I was going to propose looking into it. I'll try to find some time.