Re: [PATCH v5 4/5] c++modules: report imported CMI files as dependencies

[Ben Boeckel <ben.boeckel@kitware.com>]

On Thu, Jul 20, 2023 at 17:00:32 -0400, Nathan Sidwell wrote:
> On 7/19/23 20:47, Ben Boeckel wrote:
> > But it is inhibiting distributed builds because the distributing tool
> > would need to know:
> > 
> > - what CMIs are actually imported (here, "read the module mapper file"
> >    (in CMake's case, this is only the modules that are needed; a single
> >    massive mapper file for an entire project would have extra entries) or
> >    "act as a proxy for the socket/program specified" for other
> >    approaches);
> 
> This information is in the machine (& human) README section of the CMI.

Ok. That leaves it up to distributing build tools to figure out at
least.

> > - read the CMIs as it sends to the remote side to gather any other CMIs
> >    that may be needed (recursively);
> > 
> > Contrast this with the MSVC and Clang (17+) mechanism where the command
> > line contains everything that is needed and a single bolus can be sent.
> 
> um, the build system needs to create that command line? Where does the build 
> system get that information?  IIUC it'll need to read some file(s) to do that.

It's chained through the P1689 information in the collator as needed. No
extra files need to be read (at least with CMake's approach); certainly
not CMI files.

> > And relocatable is probably fine. How does it interact with reproducible
> > builds? Or are GCC CMIs not really something anyone should consider for
> > installation (even as a "here, maybe this can help consumers"
> > mechanism)?
> 
> Module CMIs should be considered a cacheable artifact.  They are neither object 
> files nor source files.

Sure, cachable sounds fine. What about the installation?

--Ben