[PATCH] D25337: [Modules] Add a command line option for enabling the modules feature exclusively for the Clang builtins.

[Richard Smith via cfe-commits]

rsmith added a comment.

I really don't like the command-line interface you're proposing here. It seems like it will be extremely confusing what something like `-fmodules -fexclusive-builtin-modules` means, for instance (usually, later `-f` flags override earlier ones, so does this *turn off* modules for everything other than builtin headers?). Instead, we should use a command-line interface that more naturally / obviously composes with other flags.

It seems like the behavior you want here is precisely:

  `-fmodules -fno-implicit-module-maps -fmodule-map-file=<resource dir>/include/module.modulemap`

(The `-fmodules-validate-system-headers` part would only make sense for people using clang directly from their build area; installed / released versions of clang should not need this. Adding it makes your flag compose poorly with other uses of modules.)

I'd be happy with you adding a flag that is equivalent to `-fmodule-map-file=<resource dir>/include/module.modulemap`.

Also, it seems unlikely to me that we would ever turn this on by default. It will cause havoc for distributed builds, especially ones that run compilation actions in 'clean' environments, as (for instance) it will cause the complete set of intrinsics headers to be compiled into a module on every compile. So if this is your proposed solution for slow compiles using intrinsics headers, you should be aware that this is not a complete solution to that problem.


https://reviews.llvm.org/D25337