[PATCH] D106394: [clang][pp] adds '#pragma include_instead'

[Louis Dionne via Phabricator via cfe-commits]

ldionne added a comment.

This is quite interesting, I'd love to be able to use this in libc++ (and suggest that my peers use this in Apple's libc)!

In D106394#2892832 <https://reviews.llvm.org/D106394#2892832>, @sammccall wrote:

> Eventually this seems like a reasonable thing to want for user code. What are your motivations for restricting it to system headers? (And do you think people in future will be tempted to lift them?)

The problem with extending this to non-system headers is that you need a way to tell which headers are allowed to include the detail headers and which ones are not. If a user-written library were able to use this pragma, it would need to somehow tell the compiler that its own headers are allowed to include the detail headers in the library. But that would require some notion of "header group", which, if you go down the rabbit hole, I think is roughly equivalent to implementing modules. By special-casing system headers, you sidestep this whole issue by saying "all system headers are special and they are allowed to include any other header", removing the need for something more clever. Chris can correct me if that's incorrect, but that's my understanding of the situation.


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https://reviews.llvm.org/D106394