fix Zip unsoundness (again) #141076
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fix Zip unsoundness (again) #141076
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Some history: The Zip TrustedRandomAccess specialization has tried to emulate the side-effects of the naive implementation for a long time, including backwards iteration. rust-lang#82292 tried to fix unsoundness (rust-lang#82291) in that side-effect-preservation code, but this introduced some panic-safety unsoundness (rust-lang#86443), but the fix rust-lang#86452 didn't fix it for nested Zip iterators (rust-lang#137255). Rather than piling yet another fix ontop of this heap of fixes this PR reduces the number of cases in which side-effects will be preserved; the necessary API guarantee change was approved in rust-lang#83791 but we haven't made use of that so far.
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Some history: The Zip TrustedRandomAccess specialization has tried to emulate the side-effects of the naive implementation for a long time, including backwards iteration. #82292 tried to fix unsoundness (#82291) in that side-effect-preservation code, but this introduced some panic-safety unsoundness (#86443), but the fix #86452 didn't fix it for nested Zip iterators (#137255).
Rather than piling yet another fix ontop of this heap of fixes this PR reduces the number of cases in which side-effects will be preserved; the necessary API guarantee change was approved in #83791 but we haven't made use of that so far.
fixes #137255