mirror of
https://github.com/llvm/llvm-project.git
synced 2025-04-27 22:36:06 +00:00
d4c39f1ab9
Back in 3a208c68942e, we implemented the range-based constructor for <span>. However, in doing so, we removed a previous non-standard constructor that we provided before shipping <ranges>. Unfortunately, that breaks code that was relying on a range-based constructor until we ship all of <ranges>. This patch reintroduces the old non-conforming constructors and tests that were removed in 3a208c68942e and uses them whenever <ranges> is not provided (e.g. in LLVM 14). This is only a temporary workaround until we enable <ranges> by default in C++20, which should hopefully happen by LLVM 15. The goal is to cherry-pick this workaround back to the LLVM 14 release branch, since I suspect the constructor removal may otherwise cause breakage out there, like the breakage I saw internally. We could have avoided this situation by waiting for C++20 to be finalized before shipping std::span. For example, we could have guarded it with something like _LIBCPP_HAS_NO_INCOMPLETE_RANGES to prevent users from accidentally starting to depend on it before it is stable. We did not have these mechanisms when std::span was first implemented, though. Differential Revision: https://reviews.llvm.org/D121626