[PATCH] D30882: Add a callback for __has_include and use it for dependency scanning

[Duncan P. N. Exon Smith via Phabricator via cfe-commits]

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Herald added a subscriber: kbarton.

I don't think this is quite right.  I know at least `make`-based incremental builds wouldn't deal well with this.

Given t.cpp:

  #if __has_include("missing.h")
  #endif

t.d will be:

  t.o: missing.h

Since the build system doesn't know how to generate missing.h, when t.cpp changes the build system will stop dead in its tracks.

Knowing the list of files that are //potential// inputs to `t.o` seems useful, but we should probably do that under a separate flag.  And if it's a separate flag, we might consider giving it a better name than `-MF`...


https://reviews.llvm.org/D30882