Re: "#define precompose_argv(c,v) /* empty */" is evil

> I had seen an interesting compilation breakage today.  A topic adds
> many more uses of argv-array API so I resolved semantic conflict
> patch until "make builtins/submodule-helper.o" passed.  I failed to
> spot one remaining breakage until I saw
>
>     https://travis-ci.org/github/git/git/jobs/715668996
>
> The problematic line was
>
>     precompose_argv(diff_args.argc, diff_args.argv);
>
> where diff_args used to be an argv_array and is now a strvec.
>
> Why didn't I catch this in my local test?
>
> $ git grep -n -e precompose_argv -- \*.h
> compat/precompose_utf8.h:31:void precompose_argv(int argc, const char **argv);
> git-compat-util.h:256:#define precompose_argv(c,v)
>
> The problematic part is this one used on all platforms other than macOS:
>
>     /* used on Mac OS X */
>     #ifdef PRECOMPOSE_UNICODE
>     #include "compat/precompose_utf8.h"
>     #else
>     #define precompose_str(in,i_nfd2nfc)
>     #define precompose_argv(c,v)
>     #define probe_utf8_pathname_composition()
>     #endif
>
> I am wondering if it is a good idea to use something like
>
>     static inline void precompose_argv(int argc, const char **argv)
>     {
> 	; /* nothing */
>     }
>
> instead.  As long as the compiler is reasonable enough, this should
> not result in any code change in the result, except that it would
> still catch wrong arguments, even if these two parameters are unused
> and optimized out.
>