TrustedRandomAaccess specialization composes incorrectly for nested iter::Zips #80670
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After partially consuming a Zip adapter and then wrapping it into another Zip where the adapters use their TrustedRandomAccess specializations leads to the outer adapter returning elements which should have already been consumed.
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r? @m-ou-se (rust-highfive has picked a reviewer for you, use r? to override) |
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ping @m-ou-se |
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Thanks for fixing this! @bors r+ |
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📌 Commit af2983a has been approved by |
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Looks like this bug has been there for years. Interesting that it wasn't noticed before. |
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Jan 16, 2021
Rollup of 17 pull requests Successful merges: - rust-lang#78455 (Introduce {Ref, RefMut}::try_map for optional projections in RefCell) - rust-lang#80144 (Remove giant badge in README) - rust-lang#80614 (Explain why borrows can't be held across yield point in async blocks) - rust-lang#80670 (TrustedRandomAaccess specialization composes incorrectly for nested iter::Zips) - rust-lang#80681 (Clarify what the effects of a 'logic error' are) - rust-lang#80764 (Re-stabilize Weak::as_ptr and friends for unsized T) - rust-lang#80901 (Make `x.py --color always` apply to logging too) - rust-lang#80902 (Add a regression test for rust-lang#76281) - rust-lang#80941 (Do not suggest invalid code in pattern with loop) - rust-lang#80968 (Stabilize the poll_map feature) - rust-lang#80971 (Put all feature gate tests under `feature-gates/`) - rust-lang#81021 (Remove doctree::Import) - rust-lang#81040 (doctest: Reset errors before dropping the parse session) - rust-lang#81060 (Add a regression test for rust-lang#50041) - rust-lang#81065 (codegen_cranelift: Fix redundant semicolon warn) - rust-lang#81069 (Add sample code for Rc::new_cyclic) - rust-lang#81081 (Add test for rust-lang#34792) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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I found this while working on improvements for TRA.
After partially consuming a Zip adapter and then wrapping it into another Zip where the adapters use their
TrustedRandomAccessspecializations leads to the outer adapter returning elements which should have already been consumed.If the optimizer gets tripped up by the addition this might affect performance for chained
zip()iterators even when the inner one is not partially advanced but it would require more extensive fixes toTrustedRandomAccessto communicate those offsets earlier.Included test fails on nightly, playground link