[cfe-users] Modules TS: How to get clang++ to automatically parse and precompile the necessary module files

[Manuel Bergler via cfe-users]

Hi everyone,

following Richard Smith's talk at CppCon this year where he mentioned that
Clangs Module TS implementation,
while still work in progress, can already be used to build stuff, I decided
to try it out.

So I compiled Clang 4.0 from svn, create a module interface file
'myclass.cppm' and a 'main.cpp' to test it.

I've gotten it to build successfully by executing

> clang++ -std=c++1z -fmodules-ts --precompile -o myclass.pcm myclass.cppm
> clang++ -std=c++1z -fmodules-ts -fmodule-file=myclass.pcm -o modules_test main.cpp
>
>
So far so good. But on the Modules FAQ page [1] it says:

> The binary representation of modules is automatically generated by the
> compiler on an as-needed basis.
>

Is this only implemented for Clang's "C++98 style modules" yet or am I
missing a flag I need to pass to clang++
in order for it to precompile my module automatically? Currently neither of

> clang++ -std=c++1z -fmodules-ts main.cpp
>
clang++ -std=c++1z -fmodules-ts myclass.cppm main.cpp
>
work.

Best,
Manuel

[1] http://clang.llvm.org/docs/Modules.html#compilation-model
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