[ccache] BUG: ccache + icecream + clang -Weverything results in false "warning: macro is not used [-Wunused-macros]"

[Éric Chamberland]

It looks like it is a clang bug! See icecream answer here:

https://github.com/icecc/icecream/issues/514

Eric

Le 20-01-22 à 09:20, Eric Chamberland via ccache a écrit :
> Hi,
>
> We have a simple but annoying bug with ccache (3.7.1) + icecream + 
> clang 7.0.
>
> This file:
>
> =================
>
> #define UsedMacro double
>
> double foo();
>
> double foo() {
>   UsedMacro var = 0;
>   return var;
> }
>
> =================
>
> Compiles without warnings if compiled with bare clang 7.0 like this:
>
> /usr/bin/clang -Weverything -c t.cc
>
> It compiles also without warnings if I use cache:
>
> ccache -C && /usr/lib64/ccache/clang -Weverything -c t.cc
>
> But If I add export CCACHE_PREFIX=/opt/icecream-1.2/bin/icecc, 
> resulting in this environnement:
>
> CCACHE_PREFIX=/opt/icecream-1.2/bin/icecc
> CCACHE_SLOPPINESS=include_file_mtime
> CCACHE_HARDLINK=1
> CCACHE_DIR=/d1/home/ericc/eric-ccache/
>
> then I have a "false" warning:
>
> ccache -C && /usr/lib64/ccache/clang -Weverything -c t.cc
> Cleared cache
> t.cc:1:9: warning: macro is not used [-Wunused-macros]
> #define UsedMacro double
>         ^
> 1 warning generated.
>
>
> Is it a ccache bug or an icecream bug?
>
> Thanks,
>
> Eric
>
>
-- 
Eric Chamberland, ing., M. Ing
Professionnel de recherche
GIREF/Université Laval
(418) 656-2131 poste 41 22 42