[clang][DependencyScanning] Add API to expose module CompilerInvocation

[cachemeifyoucan]

Add a new API that returns underlying CompilerInvocation from ModuleDep. This allows clients to inspect and modify the state inside CompilerInvocation before turning that into build arguments.

[jansvoboda11]

Why don't we just expose the underlying CompilerInvocation inside ModuleDeps to Swift, if it's currently happy modifying it after the Clang scan finishes?

[cachemeifyoucan]

Why don't we just expose the underlying CompilerInvocation inside ModuleDeps to Swift, if it's currently happy modifying it after the Clang scan finishes?

Isn't this patch just did something similar? Just need an entry point to modified the underlying CompilerInvocation before calling getBuildArguments(). Register in the service is less likely to cause error due to calling order of the function of conflicting callback being applied cause the cached build command out of sync. I am definitely up for better alternative if it can make API clearer.

[jansvoboda11]

Why don't we just expose the underlying CompilerInvocation inside ModuleDeps to Swift, if it's currently happy modifying it after the Clang scan finishes?

Isn't this patch just did something similar? Just need an entry point to modified the underlying CompilerInvocation before calling getBuildArguments(). Register in the service is less likely to cause error due to calling order of the function of conflicting callback being applied cause the cached build command out of sync. I am definitely up for better alternative if it can make API clearer.

I find that post-processing value-type results is much clearer compared to callbacks. I also don't think the current implementation of the callback is sound due to the ordering I mentioned in my inlined comment. If that ordering is indeed necessary, I'd prefer to delegate that to the client rather than bake that into the Clang scanner API.

[cachemeifyoucan]

If that ordering is indeed necessary, I'd prefer to delegate that to the client rather than bake that into the Clang scanner API.

Ordering is still not controlled by client if you expose internal compiler invocation because you cannot modify the invocation where you mentioned in the inline comment. You can only do it afterwards. But I am fine with adding that flexibility.

[cachemeifyoucan]

@swift-ci please test