unix: unbreak macOS < 10.14

[barracuda156]

@bnoordhuis @johnsonjh Could we have this fixed, please?

[bnoordhuis]

I'm okay with merging this (sans style nit) but, per SUPPORTED_PLATFORMS.md, the breakage is completely intentional. If Apple doesn't support it, then we don't either.

This patch might buy you some time but we remove code for unsupported platforms when it gets in the way; sooner or later something is going to break irrevocably.

[barracuda156]

@bnoordhuis Thank you! Yes, I understand that nothing is forever, but this is a trivial and non-invasive fix, which won’t hurt (at least as long as the fallback code there is present).

UPD. Made a change pointed out by @kencu to rather use MAC_OS_X_VERSION_MIN_REQUIRED and squashed commits.

[vtjnash]

Historically I don't think libuv has accepted patches for compile-time-based restrictions either, generally relying instead on runtime checks. For example, marking this a weak symbol (in the source and linker stages) and checking if it is null at runtime to decide which needs to be used.

[bnoordhuis]

@vtjnash you're not wrong but for unsupported platforms I think it's fine to not sink too much time and effort into it. I'll go ahead and merge this.

[barracuda156]

@bnoordhuis Thank you for merging!

@vtjnash My idea was to minimize needed changes, and since the fallback was already there, and these macros work reliably on macOS, there seemed to be no reason to re-implement it otherwise.

[Bo98]

This doesn't seem correct:

ssize_t pwritev(int, const struct iovec *, int, off_t) __DARWIN_NOCANCEL(pwritev) __API_AVAILABLE(macos(11.0), ios(14.0), watchos(7.0), tvos(14.0));

It should be < 110000.

I can open a PR for that though. Have had a few people on 10.15 ask me about it downstream.

[vtjnash]

these macros work reliably on macOS

This isn't exactly true though, which is why we don't historically allow build time configurations to influence the runtime behavior. It only works for you because you aren't testing various combinations of new and old build vs. runtime machines.

[barracuda156]

@vtjnash You mean, like, targeting 10.6 from 10.15 or alike? Indeed we do not normally do that, though presumably it should still work.

Availability macros are used across numerous software and come from Apple system headers. It is not something Macports invented. Perhaps I should have added that they work reliably in a standard environment. It may be possible to design a specific case to break them, but the whole issue was about fixing at least a standard basic usage.