[PATCH] D33102: [clang] Implement -Wcast-qual for C++

[David Blaikie via cfe-commits]

On Sat, Jun 10, 2017 at 3:33 AM Roman Lebedev via Phabricator <
reviews at reviews.llvm.org> wrote:

> lebedev.ri planned changes to this revision.
> lebedev.ri added a comment.
>
> In https://reviews.llvm.org/D33102#773296, @dblaikie wrote:
>
> > But sure. Could you also (manually, I guess) confirm that this matches
> GCC's cast-qual behavior (insofar as the warning fires in the same
> situations). If there are any deviations, let's chat about them.
>
>
> Great, you were right :)
> Found a false-negative:
>
>   $ cat /tmp/tst.c
>   int main() {
>     void* p1 = (void*)"txt";
>     char* p2 = (char*)"txt";
>   }
>   $ gcc -x c -Wcast-qual /tmp/tst.c
>   $ gcc -x c++ -Wcast-qual /tmp/tst.c
>   /tmp/tst.c: In function ‘int main()’:
>   /tmp/tst.c:2:21: warning: cast from type ‘const char*’ to type ‘void*’
> casts away qualifiers [-Wcast-qual]
>      void* p1 = (void*)"txt";
>                        ^~~~~
>   /tmp/tst.c:3:21: warning: cast from type ‘const char*’ to type ‘char*’
> casts away qualifiers [-Wcast-qual]
>      char* p2 = (char*)"txt";
>                        ^~~~~
>
>   $ ./bin/clang -x c -Wcast-qual /tmp/tst.c
>   $ ./bin/clang -x c++ -Wcast-qual /tmp/tst.c
>   /tmp/tst.c:3:21: warning: cast from 'const char *' to 'char *' drops
> const qualifier [-Wcast-qual]
>     char* p2 = (char*)"txt";
>                       ^
>   1 warning generated.
>
> So at least, in C++ mode, it should warn on both lines.
>

Seems reasonable that it should, yes.

(aside: You're still welcome to commit this patch as-is, and provide
patches for improvements as follow-up (mostly false positives would be more
of a concern to address before commit))


> I'm not sure, should that really not produce a warning in C?
> (gcc version 6.3.0 20170516 (Debian 6.3.0-18) )
>

Probably not, no - string literals have some weird mutability in C (& in
older versions of C++, even).

- Dave


>
>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D33102
>
>
>
>
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