[clang] [clang][modules-driver] Add dependency scan and dependency graph (PR #152770)

[Naveen Seth Hanig via cfe-commits]

naveen-seth wrote:

I wouldn’t mind this either 🙂. Admittedly, my knowledge of module internals/serialization is still shallow, but if that is no issue with the other modules maintainers, I'd be happy to.

> > and this line of PRs to add dependency scanning to the clang driver was the main blocker for CMake C++ module support.
> 
> I didn't follow this. CMake already supports C++ modules. And I lack an interesting for this since I feel the feature is majorly used for using modules without a build system. But this is only common tutorial in my mind. @naveen-seth could you clarify?

I also don’t remember this being a main blocker; my understanding is that the CMake-team and other stakeholders mainly wanted the `clang-scan-deps` functionality to be available directly from `clang` itself ([[Modules] Bi-Weekly Meetup Notes, Feb 17, 2026](https://discourse.llvm.org/t/modules-bi-weekly-meetup-notes-feb-17-2026/89851)). 

I believe this was the reasoning: https://github.com/llvm/llvm-project/issues/76726#issuecomment-1874571241
(cc: @mathstuf, @Bigcheese).

I’ll follow up on this in the next modules meeting and can draft an RFC afterward if there’s still interest.

https://github.com/llvm/llvm-project/pull/152770