Support look-around regex in builtin pattern hooks

[j178]

Closes #2731

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-18T11:24:39.931295Z	00eb8df	New commits

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[codecov]

Codecov Report

❌ Patch coverage is 93.84615% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.19%. Comparing base (0cc3a1e) to head (00eb8df).

Files with missing lines	Patch %	Lines
crates/prek/src/hooks/builtin_hooks/pattern.rs	93.84%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2732   +/-   ##
=======================================
  Coverage   94.19%   94.19%           
=======================================
  Files         142      142           
  Lines       30292    30316   +24     
=======================================
+ Hits        28534    28557   +23     
- Misses       1758     1759    +1     

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[Copilot]

🟢 Approval recommended

No unresolved review issues were identified, and approval assessments support approval.

Pull request overview

Adds look-around support to builtin pattern hooks using fancy-regex.

Changes:

• Replaces regex-automata matching.
• Adds look-around, runtime-error, and multiline tests.
• Updates documentation and dependency files.

File summaries

File	Description
docs/reference/built-in-hooks.md	Updates pattern syntax documentation.
crates/prek/tests/builtin_hooks.rs	Adds pattern-hook coverage.
crates/prek/src/hooks/builtin_hooks/pattern.rs	Implements fancy-regex matching.
crates/prek/Cargo.toml	Removes the direct dependency.
Cargo.toml	Removes the workspace dependency.
Cargo.lock	Updates locked dependencies.

Review details

• Files reviewed: 5/6 changed files
• Comments generated: 0
• Review effort level: Lite

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[Copilot]

🟢 Approval recommended

The changes are covered by regression tests and there are no unresolved review comments.

Review details

• Files reviewed: 5/6 changed files
• Comments generated: 0 new
• Review effort level: Lite

[prek-ci-bot]

📦 Cargo Bloat Comparison

.text size change: +3.25% (12.3 MiB → 12.7 MiB)

Expand for cargo-bloat output

Head Branch Results

File  .text     Size             Crate Name
0.1%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_45_0_aes_gcm_encrypt_avx512
0.1%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_45_0_aes_gcm_decrypt_avx512
0.0%   0.7%  96.5KiB              prek <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
0.0%   0.4%  52.8KiB              prek <<prek::config::hook::HookWire as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<&mut <serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
0.0%   0.4%  48.7KiB annotate_snippets annotate_snippets::renderer::render::render
0.0%   0.3%  44.9KiB              prek <<prek::config::Config as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<&mut <serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
0.0%   0.3%  41.2KiB              prek prek::run::{closure#0}
0.0%   0.3%  40.3KiB              prek <prek::cli::RunOptions as clap_builder::derive::Args>::augment_args
0.0%   0.3%  36.6KiB              prek prek::cli::run::run::run::{closure#0}
0.0%   0.2%  28.8KiB      serde_saphyr <granit_parser::scanner::Scanner<granit_parser::input::str::StrInput>>::fetch_more_tokens
0.0%   0.2%  28.4KiB      serde_saphyr <granit_parser::scanner::Scanner<granit_parser::input::str::StrInput>>::fetch_more_tokens
0.0%   0.2%  28.3KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  28.0KiB        aws_lc_sys aws_lc_0_45_0_edwards25519_scalarmuldouble_alt
0.0%   0.2%  27.5KiB        aws_lc_sys aws_lc_0_45_0_edwards25519_scalarmuldouble
0.0%   0.2%  27.1KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  27.0KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  27.0KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  27.0KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  27.0KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  25.2KiB              prek <<prek::config::update::UpdateOptions as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<&mut <serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
4.2%  86.9%  11.0MiB                   And 20294 smaller methods. Use -n N to show more.
4.8% 100.0%  12.7MiB                   .text section size, the file size is 264.2MiB

Base Branch Results

File  .text     Size             Crate Name
0.1%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_45_0_aes_gcm_encrypt_avx512
0.1%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_45_0_aes_gcm_decrypt_avx512
0.0%   0.8%  96.5KiB              prek <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
0.0%   0.4%  50.1KiB              prek <<prek::config::hook::HookWire as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<&mut <serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
0.0%   0.4%  48.7KiB annotate_snippets annotate_snippets::renderer::render::render
0.0%   0.3%  43.9KiB              prek <<prek::config::Config as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<&mut <serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
0.0%   0.3%  41.2KiB              prek prek::run::{closure#0}
0.0%   0.3%  40.3KiB              prek <prek::cli::RunOptions as clap_builder::derive::Args>::augment_args
0.0%   0.3%  36.8KiB              prek prek::cli::run::run::run::{closure#0}
0.0%   0.2%  28.8KiB      serde_saphyr <granit_parser::scanner::Scanner<granit_parser::input::str::StrInput>>::fetch_more_tokens
0.0%   0.2%  28.6KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  28.4KiB      serde_saphyr <granit_parser::scanner::Scanner<granit_parser::input::str::StrInput>>::fetch_more_tokens
0.0%   0.2%  28.0KiB        aws_lc_sys aws_lc_0_45_0_edwards25519_scalarmuldouble_alt
0.0%   0.2%  27.5KiB        aws_lc_sys aws_lc_0_45_0_edwards25519_scalarmuldouble
0.0%   0.2%  27.2KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  27.0KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  27.0KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  27.0KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  26.9KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
0.0%   0.2%  24.5KiB              prek <prek::workspace::Project>::init_hooks::{closure#0}
4.1%  86.6%  10.7MiB                   And 20201 smaller methods. Use -n N to show more.
4.7% 100.0%  12.3MiB                   .text section size, the file size is 263.5MiB

[prek-ci-bot]

⚡️ Hyperfine Benchmarks

Summary: 0 regressions, 1 improvements above the 10% threshold.

Environment

• OS: Linux 6.17.0-1022-azure
• CPU: 4 cores
• prek version: prek 0.5.3+20 (eaf675f 2026-09-18)
• Rust version: rustc 1.98.1 (48a229cea 2026-09-01)
• Hyperfine version: hyperfine 1.20.0

CLI Commands

Benchmarking basic commands in the main repo:

prek --version

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base --version	1.9 ± 0.1	1.8	2.0	1.06 ± 0.04
prek-head --version	1.8 ± 0.0	1.7	2.0	1.00

prek list

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base list	7.4 ± 0.1	7.2	7.6	1.03 ± 0.02
prek-head list	7.2 ± 0.1	7.0	7.4	1.00

prek validate-config .pre-commit-config.yaml

⏭️ Skipped: .pre-commit-config.yaml not found

prek sample-config

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base sample-config	2.2 ± 0.1	2.1	2.3	1.07 ± 0.05
prek-head sample-config	2.0 ± 0.1	1.9	2.2	1.00

Cold vs Warm Runs

Comparing first run (cold) vs subsequent runs (warm cache):

prek run --all-files (cold - no cache)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run --all-files	28.4 ± 1.7	27.4	33.0	1.04 ± 0.07
prek-head run --all-files	27.3 ± 0.9	26.2	28.7	1.00

prek run --all-files (warm - with cache)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run --all-files	27.7 ± 0.7	26.2	29.2	1.01 ± 0.03
prek-head run --all-files	27.5 ± 0.6	26.6	29.0	1.00

Full Hook Suite

Running the builtin hook suite on the benchmark workspace:

prek run --all-files (full builtin hook suite)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run --all-files	27.6 ± 0.9	25.9	29.6	1.01 ± 0.04
prek-head run --all-files	27.4 ± 0.8	25.2	29.3	1.00

Individual Hook Performance

Benchmarking each hook individually on the test repo:

prek run trailing-whitespace --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run trailing-whitespace --all-files	9.9 ± 0.4	9.4	10.9	1.03 ± 0.05
prek-head run trailing-whitespace --all-files	9.6 ± 0.2	9.1	10.1	1.00

prek run end-of-file-fixer --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run end-of-file-fixer --all-files	8.8 ± 0.3	8.2	9.8	1.01 ± 0.06
prek-head run end-of-file-fixer --all-files	8.7 ± 0.4	8.0	10.1	1.00

prek run check-json --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-json --all-files	6.4 ± 0.2	6.0	6.7	1.03 ± 0.04
prek-head run check-json --all-files	6.2 ± 0.2	5.8	6.5	1.00

prek run check-yaml --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-yaml --all-files	6.7 ± 2.6	6.0	20.4	1.11 ± 0.44
prek-head run check-yaml --all-files	6.0 ± 0.1	5.8	6.4	1.00

✅ Performance improvement for prek run check-yaml --all-files: 10.2000% faster

prek run check-toml --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-toml --all-files	6.4 ± 0.2	6.1	6.7	1.04 ± 0.05
prek-head run check-toml --all-files	6.1 ± 0.2	5.8	6.6	1.00

prek run check-xml --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-xml --all-files	6.4 ± 1.0	5.9	11.7	1.06 ± 0.18
prek-head run check-xml --all-files	6.0 ± 0.2	5.7	6.6	1.00

prek run detect-private-key --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run detect-private-key --all-files	8.9 ± 0.6	8.0	10.7	1.02 ± 0.08
prek-head run detect-private-key --all-files	8.7 ± 0.3	8.1	9.2	1.00

prek run fix-byte-order-marker --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run fix-byte-order-marker --all-files	9.9 ± 0.5	9.0	11.2	1.02 ± 0.08
prek-head run fix-byte-order-marker --all-files	9.7 ± 0.6	8.8	10.7	1.00

Installation Performance

Benchmarking hook installation (fast path hooks skip Python setup):

prek install-hooks (cold - no cache)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base install-hooks	3.7 ± 0.1	3.7	3.8	1.04 ± 0.02
prek-head install-hooks	3.6 ± 0.0	3.5	3.6	1.00

prek install-hooks (warm - with cache)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base install-hooks	3.8 ± 0.0	3.7	3.8	1.03 ± 0.01
prek-head install-hooks	3.7 ± 0.0	3.7	3.7	1.00

File Filtering/Scoping Performance

Testing different file selection modes:

prek run (staged files only)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run	17.4 ± 0.2	17.0	17.8	1.00 ± 0.02
prek-head run	17.3 ± 0.2	16.9	17.9	1.00

prek run --files '*.json' (specific file type)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run --files '*.json'	4.4 ± 0.1	4.2	4.5	1.04 ± 0.02
prek-head run --files '*.json'	4.2 ± 0.1	4.0	4.3	1.00

Workspace Discovery & Initialization

Benchmarking hook discovery and initialization overhead:

prek run --dry-run --all-files (measures init overhead)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run --dry-run --all-files	5.7 ± 0.1	5.6	5.8	1.03 ± 0.02
prek-head run --dry-run --all-files	5.5 ± 0.1	5.4	5.7	1.00

Meta Hooks Performance

Benchmarking meta hooks separately:

prek run check-hooks-apply --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-hooks-apply --all-files	6.8 ± 0.1	6.7	6.9	1.04 ± 0.02
prek-head run check-hooks-apply --all-files	6.5 ± 0.1	6.4	6.7	1.00

prek run check-useless-excludes --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-useless-excludes --all-files	6.7 ± 0.1	6.7	6.9	1.03 ± 0.01
prek-head run check-useless-excludes --all-files	6.5 ± 0.1	6.5	6.7	1.00

prek run identity --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run identity --all-files	5.9 ± 0.1	5.8	6.0	1.03 ± 0.02
prek-head run identity --all-files	5.8 ± 0.1	5.7	6.1	1.00

[Copilot]

🔵 Needs a closer look

The matching behavior may regress for non-ASCII text files, and documentation syntax references are missing.

Review details

Suppressed comments (3)

crates/prek/src/hooks/builtin_hooks/pattern.rs:86

• This changes the hooks from the previous byte-oriented utf8(false) matching to UnicodeBytes, where . and Unicode classes advance over UTF-8 code points and a raw byte such as 0x80 is not matched by .. That is a behavior regression for the existing text-file path: prek-identify classifies every byte >= 0x80 as text, so these files can still reach the hooks. Please preserve the prior byte-matching contract while adding look-around, or make the compatibility change explicit and cover it with tests.

        .bytes_mode(BytesMode::UnicodeBytes);

docs/reference/built-in-hooks.md:435

• The pattern hook documentation also drops its only syntax reference, even though this PR changes the engine specifically to support fancy-regex look-around. Please link this section to the regex engine documentation instead of leaving the accepted regex dialect unspecified.

When multiple patterns are provided, matching any one of them is sufficient.

docs/reference/built-in-hooks.md:407

• This removes the only regex-syntax reference for both filename pattern hooks, while their implementation now uses fancy-regex. Please retain a link to the regex engine documentation here so users can discover the supported look-around syntax.

Fails when the final path component (the basename) of any selected file matches a configured regular expression. When multiple patterns are provided, the hook fails when a basename matches any one of them.

• Files reviewed: 5/6 changed files
• Comments generated: 0 new
• Review effort level: Lite