How to use VC++ modules in CMake

Question

MS Visual C++ 2015 Update 1 implements the Modules proposal .

Here is an example of how it works:
Sources:

// c.ixx             |  // b.ixx                   |  // a.cpp
module GM;           |  import GM;                 |  import FM;
export void g() {}   |  module FM;                 |  int main() { f(); }
                     |  export void f() { g(); }   | 

Build commands:

set CL=/EHsc /experimental:module   # Default flags for cl.exe
cl.exe /c c.ixx                     # Produces c.obj, GM.ifc
cl.exe /c b.ixx                     # Depends on GM.ifc, produces b.obj, FM.ifc
cl.exe /c a.cpp                     # Depends on FM.ifc, produces a.obj
link.exe a.obj b.obj c.obj          # Produces a.exe

Dependency graph:

c.ixx → GM.ifc → b.ixx → FM.ifc → a.cpp
     ↘            ↓             ↙
       c.obj     b.obj    a.obj
            ↘     ↓      ↙
                 a.exe

Each module has one file.ixx with its exports.
This file will be compiled into ModuleName.ifc and file.obj .

If a file imports module M , a M.ifc file must be present.
By default cl.exe searches .ifc files in current directory, but it's possible to specify explicit names or search path:

cl.exe /c a.cpp
-- or --
cl.exe /c a.cpp /module:reference FM.ifc
-- or --
cl.exe /c a.cpp /module:search ./

So, the question is: How to use the VC++ implementation of modules in CMake ?
It's not necessary to use the MSBuild backend, Ninja is fine too.

Answer 1

I don't believe anyone has done any build system work for C++ modules at this time. It's likely we (Microsoft) will do MSBuild support first, but CMake is definitely a possibility.