build metadata without forcing full compilation

[mlwilkerson]

When the NIF compilation takes an especially long time, I find myself wishing that my CI workflow didn't have to do a final mix compile --force prior to mix rustler_precompiled.download.

As far as I can tell, all that's actually necessary at that point for rustler_precompiled.download to do its job, writing the checksums file, is for the metadata to be built and written. Normally that's done by build_metadata/1 when compiling.

Actually building the NIFs again at that point doesn't seem to be necessary. Is it?

Would it be possible to just build and write the metadata without going through the entire compilation?

[philss]

I don't think we can build the metadata from outside the build of the module. But how do you change the config in a way that needs to rebuild the metadata?

[philss]

@mlwilkerson I think you can force the recompilation of the module with the following:

$ mix run -e "Kernel.ParallelCompiler.compile([(YourNativeModuleHere).module_info(:compile)[:source]])"

This will trigger the recompilation of that module, but will skip what is already compiled. WDYT?