[Bug c/37041] -Wc++-compat refinements

[egall at gwmail dot gwu.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37041

Eric Gallager <egall at gwmail dot gwu.edu> changed:

           What    |Removed                     |Added
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                 CC|                            |egall at gwmail dot gwu.edu

--- Comment #5 from Eric Gallager <egall at gwmail dot gwu.edu> ---
A few other refinements to -Wc++-compat that I would like to see:

1. Have it properly handle stuff like the following idiom commonly found in
header files:

#ifdef __cplusplus
extern "C" {
#endif

/* code that is C-only */

#ifdef __cplusplus
}
#endif /* __cplusplus */

I would expect -Wc++-compat to treat something like the above similarly to how
the following pragmas would work:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++-compat"

/* code that -Wc++-compat should ignore */

#pragma GCC diagnostic pop

While the version with pragmas is shorter, the `extern "C"` stuff is often
needed for separate reasons, and as such, it would be nice to avoid the need to
do both...

2. Make -Wc++-compat an "umbrella" warning flag like -Wall or -Wextra.
Currently -Wc++-compat warns about many different things, and sometimes I would
like to just focus on one of those things. I can think of at least the
following sub-flags that could be split off from it:
** "-Wc++-compat-pointer-conversion" for the ones like "warning: request for
implicit conversion from 'void *' to 'char *' not permitted in C++"
** "-Wc++-compat-keywords" for the ones like "warning: identifier 'class'
conflicts with C++ keyword"
** "-Wc++-compat-visibility" for the ones like "warning: enum constant defined
in struct or union is not visible in C++" (or likewise with "struct" or "union"
instead of "enum constant")