remove solaris implementation for File::lock, it has the wrong semantics

[RalfJung]

Fixes #157390
r? @the8472

[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[the8472]

Uhh, wait... I previously misread the CFGs... I thought freebsd was also on the unsupported list. Because their manpage is pretty similar to Solaris.

https://man.freebsd.org/cgi/man.cgi?query=flock&sektion=2

NOTES
Locks are on files, not file descriptors.

And it mostly talks about processes owning the lock.

Even macos 😩: https://man.freebsd.org/cgi/man.cgi?query=flock&apropos=0&sektion=2&manpath=macOS+26.4

Considering that is a tier1 target I guess we have to relax the documentation instead.

[RalfJung]

Reading that FreeBSD manpage further, it says

That is, file descriptors
duplicated through dup(2) or fork(2) do not result in multiple in-
stances of a lock, but rather multiple references to a single lock.

That sounds like locks are on file descriptions, not file descriptors. That's quite reasonable and entirely consistent with Linux and our docs.

Also note that we have a test which ensures that locks are not per-process:

rust/library/std/src/fs/tests.rs

Lines 229 to 243 in 18159d4

	fn file_lock_blocking() {
	let tmpdir = tmpdir();
	let filename = &tmpdir.join("file_lock_blocking_test.txt");
	let f1 = check!(File::create(filename));
	let f2 = check!(OpenOptions::new().write(true).open(filename));
	// Check that shared locks block exclusive locks
	check!(f1.lock_shared());
	assert_matches!(f2.try_lock(), Err(TryLockError::WouldBlock));
	check!(f1.unlock());
	// Check that exclusive locks block shared locks
	check!(f1.lock());
	assert_matches!(f2.try_lock_shared(), Err(TryLockError::WouldBlock));
	}

This test would have failed on Solaris. It apparently passes on macOS. So I think macOS is also doing the sane thing here.

[the8472]

Hrm, ok, then the manpages are just written in a confusing manner... I guess they mean file description, not files.

@bors r+

[rust-bors]

📌 Commit 353aa6d has been approved by the8472

It is now in the queue for this repository.