Some const { } asserts for #128200
#128465
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rustc_errors: use perfect hashing for character replacements The correctness of code in rust-lang#128200 relies on an array being sorted (so that it can be used in binary search later), which is currently enforced with `// tidy-alphabetical` (and characters being written in `\u{XXXX}` form), as well as lack of duplicate entries with conflicting keys, which is not currently enforced. A const assert or a test can be added checking that (implemented in rust-lang#128465). But this PR tries to use [perfect hashing](https://en.wikipedia.org/wiki/Perfect_hash_function) instead. The performance implications are unclear. Asymptotically it's faster, but in reality we should just benchmark. Plus if there are no significant performance wins, this entire things is probably not even worse the additional dependencies it brings. UPD: funnily enough, there's a PR optimizing the binary search implementation (rust-lang#128254) in the queue right now. So I guess we have to wait until that is merged too before benchmarking this.
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| "The OUTPUT_REPLACEMENTS array must be sorted (for binary search to work) \ | ||
| and must contain no duplicate entries" |
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Should we add another check for assert_neq!(OUTPUT_REPLACEMENTS[i - 1].0, OUTPUT_REPLACEMENTS[i].0) too?
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The check is already < and not <=
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Some `const { }` asserts for rust-lang#128200
The correctness of code in rust-lang#128200 relies on an array being sorted (so that it can be used in binary search later), which is currently enforced with `// tidy-alphabetical` (and characters being written in `\u{XXXX}` form), as well as lack of duplicate entries with conflicting keys, which is not currently enforced.
This PR changes it to using a `const{ }` assertion (and also checks for duplicate entries). Sadly, we cannot use the recently-stabilized `is_sorted_by_key` here, because it is not const (but it would not allow us to check for uniqueness anyways). Instead, let's write a manual loop.
Alternative approach (perfect hash function): rust-lang#128463
r? `@ghost`
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…iaskrgr Rollup of 2 pull requests Successful merges: - rust-lang#128465 (Some `const { }` asserts for rust-lang#128200 ) - rust-lang#128795 (Update E0517 message to reflect RFC 2195.) r? `@ghost` `@rustbot` modify labels: rollup
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☀️ Test successful - checks-actions |
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Finished benchmarking commit (d3a3939): comparison URL. Overall result: no relevant changes - no action needed@rustbot label: -perf-regression Instruction countThis benchmark run did not return any relevant results for this metric. Max RSS (memory usage)Results (primary -0.1%, secondary -0.0%)This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.
CyclesThis benchmark run did not return any relevant results for this metric. Binary sizeThis benchmark run did not return any relevant results for this metric. Bootstrap: 762.874s -> 760.03s (-0.37%) |
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The correctness of code in #128200 relies on an array being sorted (so that it can be used in binary search later), which is currently enforced with
// tidy-alphabetical(and characters being written in\u{XXXX}form), as well as lack of duplicate entries with conflicting keys, which is not currently enforced.This PR changes it to using a
const{ }assertion (and also checks for duplicate entries). Sadly, we cannot use the recently-stabilizedis_sorted_by_keyhere, because it is not const (but it would not allow us to check for uniqueness anyways). Instead, let's write a manual loop.Alternative approach (perfect hash function): #128463
r? @ghost