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Include non-redundant separators in Hash for Path #127255

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Include non-redundant separators in Hash for Path #127255

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zanieb
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@zanieb zanieb commented Jul 3, 2024

Closes #127254, please see the issue for the details as I cover a lot there.

I'm not confident this is the clearest way to fix this, I'd appreciate some feedback.

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rustbot commented Jul 3, 2024

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Nilstrieb (or someone else) some time within the next two weeks.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

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@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jul 3, 2024
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zanieb commented Jul 3, 2024

cc @the8472 as I believe the regression was from your commit and you look quite active still.

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zanieb commented Jul 3, 2024

Ah I can reproduce that test failure locally — I was only testing test_compare. I'll investigate a fix.

@zanieb zanieb marked this pull request as draft July 3, 2024 02:26
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zanieb commented Jul 3, 2024
View reviewed changes
library/std/src/path/tests.rs
Comment on lines +1597 to +1602
tc!("foo/bar", "foobar",
eq: false,
starts_with: false,
ends_with: false,
relative_from: None
);
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This is the test case reported in the issue.

@the8472 the8472 assigned the8472 and unassigned Noratrieb Jul 3, 2024
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the8472 commented Jul 3, 2024

I'll take a look and will have to run some benchmarks to see the perf impact of this change, since that loop is fairly sensitive.

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the8472 commented Jul 3, 2024

Yeah, this regresses hashset performance

this PR: 
    path::tests::bench_path_hashset                   342.01/iter    +/- 8.37
    path::tests::bench_path_hashset_miss              139.03/iter    +/- 8.95

master:
    path::tests::bench_path_hashset                   244.21/iter    +/- 6.28
    path::tests::bench_path_hashset_miss              100.68/iter    +/- 9.11

I'll see if I can find an alternative that satisfies the added tests.

@the8472 the8472 mentioned this pull request Jul 3, 2024
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the8472 commented Jul 3, 2024 •
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I took your tests and added a more lightweight fix in #127297

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zanieb commented Jul 3, 2024 •
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#127297 seems like a much better approach

@zanieb zanieb closed this Jul 3, 2024
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Jul 7, 2024
@matthiaskrgr
Rollup merge of rust-lang#127297 - the8472:path-new-hash, r=Nilstrieb
56557c4 
Improve std::Path's Hash quality by avoiding prefix collisions

This adds a bit rotation to the already existing state so that the same sequence of characters chunked at different offsets into separate path components results in different hashes.

The tests are from rust-lang#127255

Closes rust-lang#127254
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Jul 7, 2024
@rust-timer
Unrolled build for rust-lang#127297
a1f5ba3 
Rollup merge of rust-lang#127297 - the8472:path-new-hash, r=Nilstrieb

Improve std::Path's Hash quality by avoiding prefix collisions

This adds a bit rotation to the already existing state so that the same sequence of characters chunked at different offsets into separate path components results in different hashes.

The tests are from rust-lang#127255

Closes rust-lang#127254
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Hash implementation for Path ignores path separators
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