[clang] [Modules] Don't fail when an unused textual header is missing. (PR #138227)

[Ben Langmuir via cfe-commits]

benlangmuir wrote:

> I don't think we can ever get rid of that pattern and we will keep relying on Clang supporting this.
> We would need to example I shared above to keep working. 
> I think the change we want is to always prioritize modular over textual, before we look at non-private vs private.

Can you clarify, are you saying this pattern of having a header in two different modules has to keep working indefinitely, or are you willing to migrate off of it?

I don't understand what the reason is for the header to be in two different modules in the first place.  It sounds like it is somehow related to a build optimization, but what exactly is that?



https://github.com/llvm/llvm-project/pull/138227