Optimize diff checks for clean worktrees by j178 · Pull Request #2109 · j178/prek

j178 · 2026-05-20T07:36:28Z

Avoid full before-and-after git diff calls when hooks run from a cleaned worktree and leave it unchanged.

Based on #1464, thanks @shaanmajid!
Closes #1464
Related #1327

codecov · 2026-05-20T07:38:51Z

Codecov Report

❌ Patch coverage is 98.14815% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.39%. Comparing base (3184e7d) to head (cefb1bd).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
crates/prek/src/cli/run/diff.rs	97.43%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2109   +/-   ##
=======================================
  Coverage   92.38%   92.39%           
=======================================
  Files         120      121    +1     
  Lines       24804    24837   +33     
=======================================
+ Hits        22915    22947   +32     
- Misses       1889     1890    +1

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Copilot

Pull request overview

This PR optimizes “did hooks modify files?” detection by avoiding full git diff snapshots when hooks run on a cleaned worktree and leave it unchanged, reducing unnecessary git invocations and I/O during hook runs.

Changes:

Introduces DiffTracker to manage baseline selection (clean/unknown/snapshot) and centralize modification detection logic.
Adds a cheap worktree diff check via git diff-files --quiet (has_worktree_diff) to short-circuit full diff generation when possible.
Expands integration tests to assert the expected number of get_diff vs has_worktree_diff calls under different scenarios (all skipped, noop, modifying hook, dirty --all-files).

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/tests/skipped_hooks.rs	Adds regression + behavior tests for optimized diff detection paths using trace log counting.
crates/prek/src/git.rs	Adds `has_worktree_diff` (quiet worktree diff check) to support the fast path.
crates/prek/src/cli/run/run.rs	Wires `DiffTracker` into hook execution to replace per-group baseline handling.
crates/prek/src/cli/run/mod.rs	Registers the new `diff` module.
crates/prek/src/cli/run/diff.rs	Implements `DiffTracker` and baseline strategies (clean vs snapshot comparisons).

prek-ci-bot · 2026-05-20T07:42:54Z

📦 Cargo Bloat Comparison

Binary size change: -0.76% (26.3 MiB → 26.1 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%  90.8KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.7%  86.3KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.6%  74.5KiB             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%  46.8KiB              prek prek::cli::run::run::run::{{closure}}
 0.1%   0.3%  35.9KiB              prek prek::run::{{closure}}
 0.1%   0.3%  32.9KiB             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%  26.4KiB              prek prek::cli::try_repo::try_repo::{{closure}}
 0.1%   0.2%  23.6KiB              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
41.5%  86.2%  10.8MiB                   And 23940 smaller methods. Use -n N to show more.
48.1% 100.0%  12.6MiB                   .text section size, the file size is 26.1MiB

Base 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

prek-ci-bot · 2026-05-20T07:42:54Z

⚡️ Hyperfine Benchmarks

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

Environment

OS: Linux 6.17.0-1013-azure
CPU: 4 cores
prek version: prek 0.4.1+3 (be24ba7 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`	1.8 ± 0.2	1.6	3.3	1.00
`prek-head --version`	2.0 ± 0.7	1.6	5.8	1.13 ± 0.39

⚠️ Warning: Performance regression for prek --version: 12.5000% slower

`prek list`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base list`	8.3 ± 1.0	7.4	13.0	1.04 ± 0.14
`prek-head list`	8.0 ± 0.5	7.4	10.3	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base validate-config .pre-commit-config.yaml`	2.5 ± 0.0	2.4	2.6	1.00 ± 0.10
`prek-head validate-config .pre-commit-config.yaml`	2.5 ± 0.2	2.3	4.0	1.00

`prek sample-config`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base sample-config`	2.2 ± 0.3	1.9	3.5	1.08 ± 0.16
`prek-head sample-config`	2.0 ± 0.0	1.9	2.1	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`	54.7 ± 1.3	52.7	56.8	1.00
`prek-head run --all-files`	57.4 ± 6.6	52.9	74.0	1.05 ± 0.12

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --all-files`	55.3 ± 2.6	51.6	62.4	1.00
`prek-head run --all-files`	55.5 ± 2.9	51.7	60.4	1.00 ± 0.07

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`	54.7 ± 1.9	52.0	61.1	1.00
`prek-head run --all-files`	54.9 ± 1.8	51.3	57.8	1.00 ± 0.05

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`	14.4 ± 0.5	13.6	15.7	1.00
`prek-head run trailing-whitespace --all-files`	14.8 ± 1.0	13.6	17.7	1.03 ± 0.08

`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`	19.7 ± 2.2	17.5	28.6	1.08 ± 0.13
`prek-head run end-of-file-fixer --all-files`	18.2 ± 0.7	17.0	19.9	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-json --all-files`	6.1 ± 0.3	5.7	6.6	1.02 ± 0.05
`prek-head run check-json --all-files`	6.0 ± 0.1	5.6	6.3	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-yaml --all-files`	5.9 ± 0.1	5.7	6.2	1.00
`prek-head run check-yaml --all-files`	6.3 ± 0.8	5.6	8.7	1.07 ± 0.13

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-toml --all-files`	6.3 ± 0.6	5.7	8.7	1.00
`prek-head run check-toml --all-files`	6.8 ± 2.2	5.6	17.7	1.09 ± 0.36

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-xml --all-files`	6.0 ± 0.2	5.6	6.6	1.03 ± 0.05
`prek-head run check-xml --all-files`	5.8 ± 0.2	5.5	6.2	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`	10.2 ± 0.6	9.5	11.6	1.03 ± 0.08
`prek-head run detect-private-key --all-files`	9.9 ± 0.5	9.1	11.5	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`	16.1 ± 0.8	14.7	18.1	1.00 ± 0.08
`prek-head run fix-byte-order-marker --all-files`	16.1 ± 1.0	14.4	18.2	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`	3.6 ± 0.0	3.5	3.6	1.02 ± 0.01
`prek-head install-hooks`	3.5 ± 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`	3.5 ± 0.1	3.5	3.6	1.00
`prek-head install-hooks`	3.6 ± 0.1	3.5	3.7	1.03 ± 0.03

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`	27.6 ± 0.7	26.4	29.7	1.01 ± 0.03
`prek-head run`	27.3 ± 0.5	26.6	28.9	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --files '*.json'`	5.9 ± 0.1	5.8	6.1	1.00
`prek-head run --files '*.json'`	6.0 ± 0.1	5.8	6.2	1.00 ± 0.02

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`	5.6 ± 0.2	5.3	5.9	1.03 ± 0.04
`prek-head run --dry-run --all-files`	5.4 ± 0.1	5.2	5.6	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`	8.9 ± 0.2	8.7	9.4	1.02 ± 0.02
`prek-head run check-hooks-apply --all-files`	8.8 ± 0.1	8.6	8.9	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`	8.8 ± 0.1	8.6	9.1	1.07 ± 0.06
`prek-head run check-useless-excludes --all-files`	8.2 ± 0.4	7.8	9.3	1.00

`prek run identity --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run identity --all-files`	7.5 ± 0.1	7.4	7.7	1.01 ± 0.02
`prek-head run identity --all-files`	7.4 ± 0.1	7.2	7.7	1.00

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Pull request overview

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chatgpt-codex-connector · 2026-05-20T08:03:22Z

+                if !git::has_worktree_diff(self.path).await? {
+                    return Ok(false);


Keep clean-baseline checks based on patch content, not exit code

Using git diff-files --quiet as the clean-baseline detector can produce false positives on CRLF-normalized worktrees: Git may return exit code 1 while git diff for the same path is empty (the same quirk already handled in WorkingTreeKeeper::clean). In that case a no-op hook is reported as having modified files, causing an otherwise successful run to fail after this commit. This regression is specific to repos/environments with line-ending normalization (e.g., core.autocrlf) and did not occur with the previous before/after get_diff content comparison.

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Copilot AI review requested due to automatic review settings May 20, 2026 07:36

Copilot started reviewing on behalf of j178 May 20, 2026 07:36 View session

j178 added the performance Performance improvements label May 20, 2026

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

Comment thread crates/prek/src/git.rs Outdated

j178 force-pushed the optimize-diff-checks branch from c23811c to 5970f7b Compare May 20, 2026 07:51

Optimize diff checks for clean worktrees

cefb1bd

Copilot AI review requested due to automatic review settings May 20, 2026 07:57

j178 force-pushed the optimize-diff-checks branch from 5970f7b to cefb1bd Compare May 20, 2026 07:57

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Comment thread crates/prek/src/git.rs

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

j178 merged commit d3b112b into master May 20, 2026
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j178 deleted the optimize-diff-checks branch May 20, 2026 08:02

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BrewTestBot mentioned this pull request May 26, 2026

prek 0.4.2 Homebrew/homebrew-core#284737

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GnoX mentioned this pull request May 26, 2026

prek 0.4.2 reports false-positive "files modified" for in-place rewrites (clean-worktree fast path) #2127

Closed

		if !git::has_worktree_diff(self.path).await? {
		return Ok(false);

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📦 Cargo Bloat Comparison

Head Branch Results

Base Branch Results

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⚡️ 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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`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`