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

[David Blaikie via Phabricator via cfe-commits]

dblaikie added a comment.

In D106394#2922972 <https://reviews.llvm.org/D106394#2922972>, @rsmith wrote:

> ... As an alternative, have you considered checking whether any of the headers named in the pragma are in the include stack, and warning if not? That would seem to make this warning applicable to both user headers and system headers in an unsurprising way. We'd presumably need two lists of headers: the external headers that we encourage people to include to get at the implementation detail header, and the internal list of headers that are also allowed to use it but that we shouldn't list in the diagnostic.

Yeah, @cjdb and I discussed this offline last week - a main concern with that direction is the maintenance burden that'd add to libc++ when using one of the internal implementation headers, having to update the "internal list of headers" every time a new include is added. Not impossible, but maybe impractical - especially for more common internal headers (like whatever provides std::move, maybe needing to be included in nearly every file.

(we speculated that maybe something akin to a modulemap could be used - found with a similar search path that would be able to describe once a single set of headers (but I guess that only works if all the headers are in a partitioned subdirectory - otherwise who gets to own the top-level file that has these lists of names - I guess maybe each file could say "I'm part of library foo" and then from the file search for foo.headerlist file and use that to describe which are the public and private headers to implement the warning) - but no doubt that's overkill/not likely feasible)


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