feat: Clang module map `requires swift` feature

[torarnv]

As described in https://discourse.llvm.org/t/module-map-requires-as-non-hard-requirement/88589 we're looking for a way to provide Clang module maps for Qt for use with Swift, in a way that guarantees these module maps are not accidentally picked up when building C++/Objective-C code (to avoid #158249 and other possible issues).

If #163965 is implemented we can provide optional module maps, but there is currently no declared feature that would detect whether the current compilation unit is built to support Swift C++ interopt.

It would be nice if there was a swift or similar feature, that could be used to limit a Clang module map to only Swift C++ interopt consumers.

Thanks! 🙂

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: Tor Arne Vestbø (torarnv)

As described in https://discourse.llvm.org/t/module-map-requires-as-non-hard-requirement/88589 we're looking for a way to provide Clang module maps for Qt for use with Swift, in a way that guarantees these module maps are not accidentally picked up when building C++/Objective-C code (to avoid https://github.com//issues/158249 and other possible issues).

If #163965 is implemented we can provide optional module maps, but there is currently no declared feature that would detect whether the current compilation unit is built to support Swift C++ interopt.

It would be nice if there was a swift or similar feature, that could be used to limit a Clang module map to only Swift C++ interopt consumers.

Thanks! 🙂

[shafik]

CC @Bigcheese @rjmccall