Re: Naming flag for specifying the output file name for Binary Module Interface files

[Nathan Sidwell <nathan@acm.org>]

On 12/6/22 16:03, David Blaikie wrote:
> Over in https://reviews.llvm.org/D137059 we're discussing the naming
> of a clang flag - would be good to have it be consistent with GCC.
> 
> The functionality is to name the BMI (.pcm in Clang's parlance) output
> file when compiling a C++20 module.
> 
> Current proposal is to use `-fsave-std-cxx-module-file=` which is
> certainly precise, but maybe a bit verbose. Clang has some other flags
> related to modules that skip the std/cxx parts, and are just
> `-fmodule-*` or `-fmodules-*`, so there's some precedent for that too.
> 
> Do GCC folks have any veto votes (is the currently proposed name
> especially objectionable/wouldn't be acceptable in GCC) or preferences
> (suggestions to add to the pool)?

I think the suggested option name is problematic for a number of additional reasons:

1) 'save' -- does it *cause* the bmi to be saved, or is that actually controlled 
by other options?  (I suspect the latter)

2) 'std' -- why is this there.  There's only one C++ std, with different 
variants thereof being temporally selectable.

3) 'cxx' -- why not 'c++'?  Let's not let this transliteration of + to x get 
into the options -- it hasn't in '-std=c++20' for example.

Might I suggest something more like '-fmodule-output='?  That collates nicely 
with other -fmodule-$FOO options, and the 'output' part is similar to the 
mnemonic '-o' for the regular output file naming.  (Incidentally, as clang 
treats the BMI as a step in the compilation pipeline, what do you do if you just 
want compilation to produce the BMI and no assembly artifact?  Does '-o' name 
the BMI in that case?)

nathan

-- 
Nathan Sidwell