Skip diff checks for read-only hooks by j178 · Pull Request #2108 · j178/prek

j178 · 2026-05-20T06:45:52Z

Avoid before-and-after git diff checks for native hooks that cannot modify files, while keeping modification detection for fixers and other hooks that may write files.

For #1327

codecov · 2026-05-20T06:47:44Z

Codecov Report

❌ Patch coverage is 91.83673% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.38%. Comparing base (871b9ed) to head (6adb024).

Files with missing lines	Patch %	Lines
crates/prek/src/hooks/mod.rs	80.95%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2108   +/-   ##
=======================================
  Coverage   92.37%   92.38%           
=======================================
  Files         120      120           
  Lines       24772    24804   +32     
=======================================
+ Hits        22883    22914   +31     
- Misses       1889     1890    +1

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Copilot

Pull request overview

This PR reduces unnecessary git diff invocations during hook runs by only performing before/after diff checks for priority groups that contain hooks which may modify files, while skipping diff detection for read-only native (builtin / fast-path) hooks.

Changes:

Added per-hook “may modify files” classification for builtin hooks and fast-path pre-commit-hooks.
Refactored fast-path detection into a helper and updated run_fast_path to use it.
Updated the run loop to lazily capture and compare diffs only when a priority group includes file-modifying hooks; added an integration test asserting no diff detection for a read-only builtin hook.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
`crates/prek/src/cli/run/run.rs`	Lazily captures `git diff` baseline and compares diffs only for priority groups that may modify files.
`crates/prek/src/hooks/mod.rs`	Refactors fast-path resolution and introduces `hooks::may_modify_files` routing by repo type.
`crates/prek/src/hooks/pre_commit_hooks/mod.rs`	Adds `PreCommitHooks::may_modify_files()` classification for fast-path `pre-commit-hooks`.
`crates/prek/src/hooks/builtin_hooks/mod.rs`	Adds `BuiltinHooks::may_modify_files()` classification for builtin hooks.
`crates/prek/tests/skipped_hooks.rs`	Adds regression test verifying read-only builtin hooks do not trigger diff detection.

prek-ci-bot · 2026-05-20T06:52:15Z

📦 Cargo Bloat Comparison

Binary size change: +0.00% (26.3 MiB → 26.3 MiB)

Expand for cargo-bloat output

Head Branch Results

 File  .text     Size             Crate Name
 1.2%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_41_0_aes_gcm_encrypt_avx512
 1.2%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_41_0_aes_gcm_decrypt_avx512
 0.3%   0.7%  91.3KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.7%  86.4KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.6%  74.7KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.3%   0.5%  70.0KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.4%  51.3KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.4%  48.7KiB              prek prek::run::{{closure}}
 0.2%   0.3%  42.6KiB              prek prek::cli::run::run::run::{{closure}}
 0.1%   0.3%  33.3KiB             prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.1%   0.2%  30.4KiB             prek? <prek::config::_::<impl serde_core::de::Deserialize for prek::config::Config>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map
 0.1%   0.2%  30.2KiB               std core::ptr::drop_in_place<prek::languages::<impl prek::config::Language>::install::{{closure}}>
 0.1%   0.2%  28.1KiB      serde_saphyr granit_parser::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2%  28.0KiB        aws_lc_sys aws_lc_0_41_0_edwards25519_scalarmuldouble_alt
 0.1%   0.2%  27.5KiB        aws_lc_sys aws_lc_0_41_0_edwards25519_scalarmuldouble
 0.1%   0.2%  26.5KiB              prek prek::cli::try_repo::try_repo::{{closure}}
 0.1%   0.2%  23.7KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2%  23.0KiB      serde_saphyr granit_parser::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2%  22.3KiB         [Unknown] Lp384_montjscalarmul_alt_p384_montjadd
 0.1%   0.2%  21.5KiB      clap_builder clap_builder::parser::parser::Parser::get_matches_with
41.7%  86.2%  11.0MiB                   And 23983 smaller methods. Use -n N to show more.
48.4% 100.0%  12.7MiB                   .text section size, the file size is 26.3MiB

Base Branch Results

 File  .text     Size             Crate Name
 1.2%   2.5% 332.0KiB        aws_lc_sys aws_lc_0_41_0_aes_gcm_encrypt_avx512
 1.2%   2.5% 332.0KiB        aws_lc_sys aws_lc_0_41_0_aes_gcm_decrypt_avx512
 0.3%   0.7%  92.5KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.7%  86.6KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.6%  74.7KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.3%   0.5%  70.0KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.4%  51.3KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.4%  48.7KiB              prek prek::run::{{closure}}
 0.2%   0.3%  42.3KiB              prek prek::cli::run::run::run::{{closure}}
 0.1%   0.3%  33.3KiB             prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.1%   0.2%  30.4KiB             prek? <prek::config::_::<impl serde_core::de::Deserialize for prek::config::Config>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map
 0.1%   0.2%  30.2KiB               std core::ptr::drop_in_place<prek::languages::<impl prek::config::Language>::install::{{closure}}>
 0.1%   0.2%  28.1KiB      serde_saphyr granit_parser::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2%  28.0KiB        aws_lc_sys aws_lc_0_41_0_edwards25519_scalarmuldouble_alt
 0.1%   0.2%  27.5KiB        aws_lc_sys aws_lc_0_41_0_edwards25519_scalarmuldouble
 0.1%   0.2%  26.3KiB              prek prek::cli::try_repo::try_repo::{{closure}}
 0.1%   0.2%  23.7KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2%  23.0KiB      serde_saphyr granit_parser::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2%  22.3KiB         [Unknown] Lp384_montjscalarmul_alt_p384_montjadd
 0.1%   0.2%  21.5KiB      clap_builder clap_builder::parser::parser::Parser::get_matches_with
41.8%  86.2%  11.0MiB                   And 23993 smaller methods. Use -n N to show more.
48.4% 100.0%  12.7MiB                   .text section size, the file size is 26.3MiB

prek-ci-bot · 2026-05-20T06:52:15Z

⚡️ Hyperfine Benchmarks

Summary: 3 regressions, 13 improvements above the 10% threshold.

Environment

OS: Linux 6.17.0-1013-azure
CPU: 4 cores
prek version: prek 0.4.1+2 (cf58967 2026-05-20)
Rust version: rustc 1.95.0 (59807616e 2026-04-14)
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 ± 0.0	1.8	2.1	1.00
`prek-head --version`	1.9 ± 0.1	1.8	2.2	1.00 ± 0.04

`prek list`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base list`	7.7 ± 2.4	7.1	31.0	1.00
`prek-head list`	8.1 ± 3.4	7.2	31.5	1.05 ± 0.55

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base validate-config .pre-commit-config.yaml`	2.7 ± 0.6	2.6	6.7	1.00
`prek-head validate-config .pre-commit-config.yaml`	3.2 ± 3.6	2.5	27.8	1.16 ± 1.33

⚠️ Warning: Performance regression for prek validate-config .pre-commit-config.yaml: 15.5600% slower

`prek sample-config`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base sample-config`	2.1 ± 0.0	2.1	2.3	1.00
`prek-head sample-config`	2.3 ± 1.0	2.1	9.1	1.09 ± 0.46

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`	111.7 ± 1.0	110.2	113.5	1.83 ± 0.06
`prek-head run --all-files`	61.1 ± 2.1	58.1	63.9	1.00

✅ Performance improvement for prek run --all-files (cold - no cache): 45.3500% faster

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --all-files`	113.0 ± 4.6	107.1	128.5	1.78 ± 0.16
`prek-head run --all-files`	63.5 ± 5.0	58.3	76.5	1.00

✅ Performance improvement for prek run --all-files (warm - with cache): 43.7900% faster

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`	114.2 ± 5.8	107.0	136.4	1.74 ± 0.46
`prek-head run --all-files`	65.4 ± 17.0	58.0	179.0	1.00

✅ Performance improvement for prek run --all-files (full builtin hook suite): 42.7000% faster

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`	17.0 ± 0.5	16.1	18.2	1.06 ± 0.05
`prek-head run trailing-whitespace --all-files`	16.1 ± 0.5	15.3	17.6	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`	27.8 ± 32.2	18.5	194.1	1.23 ± 1.45
`prek-head run end-of-file-fixer --all-files`	22.7 ± 5.2	18.7	43.7	1.00

✅ Performance improvement for prek run end-of-file-fixer --all-files: 18.6600% faster

`prek run check-json --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-json --all-files`	24.1 ± 40.3	9.0	169.0	3.05 ± 5.50
`prek-head run check-json --all-files`	7.9 ± 5.2	6.2	29.7	1.00

✅ Performance improvement for prek run check-json --all-files: 67.2700% faster

`prek run check-yaml --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-yaml --all-files`	14.4 ± 28.8	9.0	167.1	1.73 ± 3.81
`prek-head run check-yaml --all-files`	8.3 ± 7.7	6.2	46.7	1.00

✅ Performance improvement for prek run check-yaml --all-files: 42.3200% faster

`prek run check-toml --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-toml --all-files`	9.8 ± 3.2	8.9	26.6	1.51 ± 0.49
`prek-head run check-toml --all-files`	6.5 ± 0.2	6.1	6.9	1.00

✅ Performance improvement for prek run check-toml --all-files: 33.9900% faster

`prek run check-xml --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-xml --all-files`	11.5 ± 5.4	9.3	34.1	1.54 ± 0.83
`prek-head run check-xml --all-files`	7.5 ± 2.0	6.7	17.9	1.00

✅ Performance improvement for prek run check-xml --all-files: 34.8800% faster

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run detect-private-key --all-files`	20.7 ± 24.7	12.5	147.7	1.00
`prek-head run detect-private-key --all-files`	86.5 ± 137.0	9.4	373.4	4.18 ± 8.28

⚠️ Warning: Performance regression for prek run detect-private-key --all-files: 317.8100% slower

`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`	18.2 ± 3.7	15.6	36.1	1.00
`prek-head run fix-byte-order-marker --all-files`	30.9 ± 55.0	15.9	300.2	1.70 ± 3.04

⚠️ Warning: Performance regression for prek run fix-byte-order-marker --all-files: 69.7400% slower

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`	3.9 ± 0.1	3.8	3.9	1.01 ± 0.02
`prek-head install-hooks`	3.8 ± 0.1	3.7	3.9	1.00

`prek install-hooks (warm - with cache)`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base install-hooks`	3.9 ± 0.1	3.8	4.0	1.01 ± 0.02
`prek-head install-hooks`	3.8 ± 0.0	3.8	3.9	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`	42.1 ± 9.0	38.5	79.0	1.16 ± 0.58
`prek-head run`	36.3 ± 16.3	31.5	105.1	1.00

✅ Performance improvement for prek run (staged files only): 13.6900% faster

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --files '*.json'`	7.7 ± 4.0	6.6	24.6	1.13 ± 0.59
`prek-head run --files '*.json'`	6.8 ± 0.1	6.6	7.0	1.00

✅ Performance improvement for prek run --files '*.json' (specific file type): 11.6200% faster

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`	9.1 ± 2.1	8.3	18.0	1.52 ± 0.36
`prek-head run --dry-run --all-files`	6.0 ± 0.1	5.8	6.1	1.00

✅ Performance improvement for prek run --dry-run --all-files (measures init overhead): 34.2900% faster

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`	19.2 ± 36.6	8.8	151.1	2.13 ± 4.06
`prek-head run check-hooks-apply --all-files`	9.0 ± 0.1	8.9	9.2	1.00

✅ Performance improvement for prek run check-hooks-apply --all-files: 53.1000% faster

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-useless-excludes --all-files`	9.5 ± 2.2	8.7	17.5	1.07 ± 0.25
`prek-head run check-useless-excludes --all-files`	8.9 ± 0.1	8.8	9.1	1.00

`prek run identity --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run identity --all-files`	14.4 ± 23.5	8.1	99.3	1.56 ± 2.56
`prek-head run identity --all-files`	9.2 ± 1.4	8.5	14.1	1.00

✅ Performance improvement for prek run identity --all-files: 35.9100% faster

Skip diff checks for read-only hooks

6adb024

Copilot AI review requested due to automatic review settings May 20, 2026 06:45

Copilot started reviewing on behalf of j178 May 20, 2026 06:46 View session

j178 added the performance Performance improvements label May 20, 2026

Copilot AI reviewed May 20, 2026

View reviewed changes

Comment thread crates/prek/src/cli/run/run.rs

Comment thread crates/prek/src/hooks/mod.rs

Comment thread crates/prek/src/hooks/mod.rs

j178 merged commit 3184e7d into master May 20, 2026
35 checks passed

j178 deleted the skip-readonly-diff branch May 20, 2026 07:11

BrewTestBot mentioned this pull request May 26, 2026

prek 0.4.2 Homebrew/homebrew-core#284737

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Pull request overview

Reviewed changes

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prek-ci-bot Bot commented May 20, 2026

📦 Cargo Bloat Comparison

Head Branch Results

Base Branch Results

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prek-ci-bot Bot commented May 20, 2026

⚡️ Hyperfine Benchmarks

prek --version

prek list

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

prek sample-config

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

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

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

prek run trailing-whitespace --all-files

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

prek run check-json --all-files

prek run check-yaml --all-files

prek run check-toml --all-files

prek run check-xml --all-files

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

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

prek install-hooks (cold - no cache)

prek install-hooks (warm - with cache)

prek run (staged files only)

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

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

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

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

prek run identity --all-files

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j178 commented May 20, 2026 •

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`prek --version`

`prek list`

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

`prek sample-config`

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

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

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

`prek run trailing-whitespace --all-files`

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

`prek run check-json --all-files`

`prek run check-yaml --all-files`

`prek run check-toml --all-files`

`prek run check-xml --all-files`

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

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

`prek install-hooks (cold - no cache)`

`prek install-hooks (warm - with cache)`

`prek run (staged files only)`

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

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

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

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

`prek run identity --all-files`