rust Revert unsound libcore changes

fixes #120537

these were introduced in #119911

Feb 01 '24 22:02 oli-obk

r? @cuviper

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Feb 01 '24 22:02 rustbot

@bors treeclosed=100 CI is stalled again.

Feb 01 '24 23:02 Mark-Simulacrum

I don't think reverting the whole thing is necessary because the unsoundness can be fixed by just adding a - 1. However, if you do decide revert it, I'll take my time rewriting it, because there are some parts that could use more attention.

Feb 02 '24 15:02 NCGThompson

@NCGThompson do you plan to submit a fix PR? If so, feel free to tag me as the reviewer, and please do include more tests of the boundary conditions, both Some and None cases.

Feb 02 '24 18:02 cuviper

I'd like to land this PR first so we don't end up with it in beta. Afterwards reverting this PR again and applying a fix should not be much effort

Feb 02 '24 18:02 oli-obk

Fair enough! I'm not sure what's going to happen with beta branching around the current tree closure, but can queue it up and also beta-backport if needed.

@bors r+ rollup

Feb 02 '24 19:02 cuviper

:pushpin: Commit 6ac035df442a27cf9e99ab4ec25bb6147a700902 has been approved by cuviper

It is now in the queue for this repository.

Feb 02 '24 19:02 bors

:evergreen_tree: The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

Feb 02 '24 19:02 bors

#120537 is a regression in 1.77 that this fixes (by revert).

@rustbot label +beta-nominated

Feb 04 '24 23:02 cuviper

Unilaterally accepting for beta backport. This is a soundness fix after all, and just a revert, so danger-free

Feb 05 '24 03:02 oli-obk