On Wed, 7 Dec 2022, 02:30 chuanqi.xcq via Gcc, <gcc@gcc.gnu.org> wrote:
> Hi Nathan, > > 1) 'save' -- does it *cause* the bmi to be saved, or is that actually > controlled > by other options? (I suspect the latter) > Yes, it causes the bmi to be saved. In fact, when we add `-save-temps` > option in clang and we compile a module unit, we'll see the preprocessed > output, the bmi, the LLVM IR and the assembly code. So the semantics of the > option `-fsave-std-cxx-module-file=` is to save the bmi to the specified > output. > > 2) 'std' -- why is this there. There's only one C++ std, with different > variants thereof being temporally selectable. > Since in clang we have clang c++ modules extension. It is not std one. And > we have objective C modules in clang too. So we said `std-cxx`. > > 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. > `c++` should be good advice. > > 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. > My previous concern was there were tons of `-fmodule-*` options in clang, > which are not standard c++ modules. So I was afraid the name > `-fmodule-output` may be confusing. > So I proposed `-fsave-std-cxx-module-file=`. But I didn't recognize we > need to keep the option consistency between gcc and clang until Iain > mentioned it. > It is obviously redundant for gcc to keep the `-std-cxx` prefix in the > name. Personally, I feel the clearity of the option name is more important > than the length. > I disagree. I can easily remember "module output" but I would have to check the manual every time to see if it's "std c++ module save file" or some other permutation of those words And if the flag is not consistent between clang and GCC that's even worse. Since I think such flags will be mainly used by build systems/build scripts > so such flags wouldn't be typed frequently. > But command line interface consistency is very important too. I know tools > writer will hate to write tons of codes like: > ``` > if compiler == gcc > ... > elif compiler == clang > ... > ``` > So I think the conclusion may be: > (1) If gcc can tolerate the lengthy `-fsave-std-c++-module-file=` name, it > would be best for clang. > IMHO that's unacceptable for GCC. (2) If (1) is not acceptable and we love to keep the command line > consistency, I think clang can use '-fmodule-output=' as long as we make it > clear in the document. It will be confusing but it may be the cost clang > need to pay for the extension (so I'll vote against strongly if someone > want to add some other extensions) > Given that C++20 modules are in an ISO standard and clang modules aren't, I think it's right that the "simple" name refers to C++20 modules, without requiring "std-c++-modules". It also seems right that the difficulty of distinguishing clang modules from std modules should be dealt with by clang, not by other compilers.
