Avoid building JSON trees in syntax hooks by j178 · Pull Request #2156 · j178/prek

j178 · 2026-06-06T06:38:22Z

No description provided.

codecov · 2026-06-06T06:39:56Z

Codecov Report

❌ Patch coverage is 80.76923% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.63%. Comparing base (671d33b) to head (006096b).

Files with missing lines	Patch %	Lines
...ates/prek/src/hooks/pre_commit_hooks/check_json.rs	80.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2156      +/-   ##
==========================================
- Coverage   92.63%   92.63%   -0.01%     
==========================================
  Files         122      122              
  Lines       26179    26167      -12     
==========================================
- Hits        24251    24239      -12     
  Misses       1928     1928

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prek-ci-bot · 2026-06-06T06:45:18Z

📦 Cargo Bloat Comparison

Binary size change: -0.38% (26.3 MiB → 26.2 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%  86.7KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.7%  86.2KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.5%  69.8KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.5%  65.2KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.2%   0.4%  49.4KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.4%  48.9KiB              prek prek::run::{{closure}}
 0.2%   0.3%  44.6KiB              prek prek::cli::run::run::run::{{closure}}
 0.1%   0.2%  31.9KiB             prek? <prek::cli::RunOptions as clap_builder::derive::Args>::augment_args
 0.1%   0.2%  30.6KiB             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%  30.1KiB               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%  23.0KiB      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%  21.8KiB     serde_saphyr? <serde_saphyr::de::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map
 0.1%   0.2%  21.5KiB      clap_builder clap_builder::parser::parser::Parser::get_matches_with
41.7%  86.3%  11.0MiB                   And 24090 smaller methods. Use -n N to show more.
48.3% 100.0%  12.7MiB                   .text section size, the file size is 26.2MiB

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%  86.8KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.7%  85.5KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.5%  69.9KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.5%  65.1KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.2%   0.4%  49.5KiB              prek prek::run::{{closure}}
 0.2%   0.4%  49.4KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.3%  44.1KiB              prek prek::cli::run::run::run::{{closure}}
 0.1%   0.2%  31.8KiB             prek? <prek::cli::RunOptions 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%  26.1KiB              prek prek::cli::try_repo::try_repo::{{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%  21.9KiB     serde_saphyr? <serde_saphyr::de::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map
 0.1%   0.2%  21.5KiB      clap_builder clap_builder::parser::parser::Parser::get_matches_with
41.7%  86.3%  10.9MiB                   And 24108 smaller methods. Use -n N to show more.
48.3% 100.0%  12.7MiB                   .text section size, the file size is 26.3MiB

prek-ci-bot · 2026-06-06T06:45:18Z

⚡️ Hyperfine Benchmarks

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

Environment

OS: Linux 6.17.0-1015-azure
CPU: 4 cores
prek version: prek 0.4.4+6 (c9ecfcf 2026-06-06)
Rust version: rustc 1.96.0 (ac68faa20 2026-05-25)
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`	2.4 ± 0.1	2.3	2.8	1.03 ± 0.04
`prek-head --version`	2.3 ± 0.0	2.2	2.4	1.00

`prek list`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base list`	9.2 ± 0.4	8.9	12.7	1.00
`prek-head list`	9.2 ± 1.0	8.9	18.8	1.00 ± 0.11

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base validate-config .pre-commit-config.yaml`	3.1 ± 0.1	3.1	3.3	1.00
`prek-head validate-config .pre-commit-config.yaml`	3.2 ± 0.1	3.0	3.3	1.01 ± 0.03

`prek sample-config`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base sample-config`	2.7 ± 0.0	2.6	2.7	1.01 ± 0.02
`prek-head sample-config`	2.6 ± 0.0	2.5	2.8	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`	76.7 ± 2.3	72.0	79.7	1.00
`prek-head run --all-files`	78.8 ± 3.4	73.1	83.9	1.03 ± 0.05

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --all-files`	78.4 ± 3.1	73.1	83.0	1.03 ± 0.06
`prek-head run --all-files`	76.3 ± 3.8	71.8	85.6	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`	78.8 ± 4.1	72.1	87.8	1.00 ± 0.07
`prek-head run --all-files`	78.5 ± 3.5	72.6	85.3	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`	20.6 ± 0.4	20.1	21.7	1.00
`prek-head run trailing-whitespace --all-files`	20.9 ± 0.9	19.8	24.1	1.01 ± 0.05

`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 ± 2.6	24.1	33.7	1.02 ± 0.12
`prek-head run end-of-file-fixer --all-files`	27.3 ± 2.1	24.1	30.8	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-json --all-files`	8.1 ± 0.2	7.6	8.6	1.00
`prek-head run check-json --all-files`	8.4 ± 1.0	7.6	12.8	1.04 ± 0.12

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-yaml --all-files`	8.0 ± 0.3	7.6	9.0	1.02 ± 0.06
`prek-head run check-yaml --all-files`	7.9 ± 0.3	7.6	9.2	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-toml --all-files`	8.1 ± 0.2	7.7	8.4	1.00 ± 0.07
`prek-head run check-toml --all-files`	8.0 ± 0.5	7.5	10.3	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-xml --all-files`	8.1 ± 0.3	7.5	8.8	1.00
`prek-head run check-xml --all-files`	8.3 ± 0.5	7.7	9.5	1.02 ± 0.07

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run detect-private-key --all-files`	14.6 ± 1.5	11.8	18.2	1.04 ± 0.15
`prek-head run detect-private-key --all-files`	14.0 ± 1.3	12.5	17.5	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`	23.3 ± 1.9	19.9	30.6	1.00
`prek-head run fix-byte-order-marker --all-files`	23.5 ± 1.8	20.1	26.4	1.01 ± 0.11

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`	4.8 ± 0.1	4.6	5.0	1.02 ± 0.03
`prek-head install-hooks`	4.7 ± 0.1	4.6	4.8	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base install-hooks`	4.8 ± 0.0	4.7	4.8	1.01 ± 0.01
`prek-head install-hooks`	4.7 ± 0.1	4.7	4.8	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`	40.7 ± 1.4	39.2	44.3	1.00
`prek-head run`	41.7 ± 2.1	39.2	47.8	1.02 ± 0.06

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --files '*.json'`	9.1 ± 0.8	8.5	11.1	1.00
`prek-head run --files '*.json'`	9.3 ± 0.9	8.8	12.3	1.03 ± 0.13

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`	20.6 ± 34.2	7.4	142.7	2.85 ± 4.73
`prek-head run --dry-run --all-files`	7.2 ± 0.1	7.1	7.4	1.00

✅ Performance improvement for prek run --dry-run --all-files (measures init overhead): 64.9100% 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`	12.6 ± 0.1	12.5	12.9	1.00 ± 0.03
`prek-head run check-hooks-apply --all-files`	12.6 ± 0.4	11.3	12.9	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`	11.4 ± 0.2	11.1	11.7	1.00 ± 0.03
`prek-head run check-useless-excludes --all-files`	11.4 ± 0.2	11.2	11.8	1.00

`prek run identity --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run identity --all-files`	10.7 ± 0.1	10.6	11.0	1.02 ± 0.01
`prek-head run identity --all-files`	10.5 ± 0.1	10.4	10.8	1.00

Copilot

Pull request overview

This pull request optimizes JSON/JSON5 syntax hooks by avoiding construction of an in-memory JSON tree while still detecting duplicate object keys, reducing memory pressure and eliminating the need for custom “careful drop” logic.

Changes:

Replaces the prior JsonValue tree-building deserializer with a lightweight JsonDuplicateKeyChecker that traverses the input and errors on duplicate keys.
Updates the JSON5 hook to reuse the same duplicate-key-checking deserializer.
Keeps deep-nesting handling via serde_stacker while removing the now-unnecessary manual drop traversal.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
crates/prek/src/hooks/pre_commit_hooks/check_json.rs	Switches to a non-tree-building deserializer that only checks duplicate keys while traversing JSON.
crates/prek/src/hooks/builtin_hooks/check_json5.rs	Uses the shared duplicate-key checker when parsing JSON5.

This MR contains the following updates: | Package | Update | Change | |---|---|---| | [prek](https://github.com/j178/prek) | patch | `0.4.4` → `0.4.5` | MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot). **Proposed changes to behavior should be submitted there as MRs.** --- ### Release Notes <details> <summary>j178/prek (prek)</summary> ### [`v0.4.5`](https://github.com/j178/prek/blob/HEAD/CHANGELOG.md#045) [Compare Source](j178/prek@v0.4.4...v0.4.5) Released on 2026-06-15. ##### ✨Highlights 0.4.5 completes `prek`'s pre-commit language coverage. With R, Conda, Perl, and coursier now supported, `prek` supports every language available in pre-commit, plus `prek`-only modern languages such as Bun and Deno. This is full feature parity with pre-commit. The last major compatibility gap is closed, and `prek` is now on the path to 1.0. ##### 💚 Sponsorship If `prek` saves time for you or your team, please consider sponsoring the project on [GitHub Sponsors](https://github.com/sponsors/j178). It helps keep new features, performance work, and maintenance moving. ##### Enhancements - Add `Perl` language support ([#2201](j178/prek#2201)) - Add `R` language support ([#2206](j178/prek#2206)) - Add `Conda` language support ([#2203](j178/prek#2203)) - Add `coursier` language support ([#2194](j178/prek#2194)) - Add group filters to list ([#2152](j178/prek#2152)) - Remove legacy repo path support ([#2150](j178/prek#2150)) - Skip cloning fully filtered remote repos ([#2151](j178/prek#2151)) ##### Performance - Avoid building JSON trees in syntax hooks ([#2156](j178/prek#2156)) - Scan mixed line endings without line vector ([#2160](j178/prek#2160)) - Skip file scan for always-run no-filename hooks ([#2155](j178/prek#2155)) - Use fixed buffer for EOF scan ([#2163](j178/prek#2163)) - Use fixed buffer for private key scan ([#2164](j178/prek#2164)) ##### Bug fixes - Fix pretty-format-json CRLF handling ([#2210](j178/prek#2210)) - Handle missing blobs in diff snapshots ([#2211](j178/prek#2211)) - Ignore coursier channel from working repo ([#2202](j178/prek#2202)) ##### Contributors - [@j178](https://github.com/j178) </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - At any time (no schedule defined) - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this MR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this MR, check this box --- This MR has been generated by [Mend Renovate](https://github.com/renovatebot/renovate).

Avoid building JSON trees in syntax hooks

006096b

j178 added the performance Performance improvements label Jun 6, 2026

j178 marked this pull request as ready for review June 6, 2026 06:44

Copilot AI review requested due to automatic review settings June 6, 2026 06:44

Copilot started reviewing on behalf of j178 June 6, 2026 06:44

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Copilot AI reviewed Jun 6, 2026

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j178 merged commit b6a45c2 into master Jun 6, 2026
35 checks passed

j178 deleted the perf-builtin-hooks branch June 6, 2026 06:48

BrewTestBot mentioned this pull request Jun 15, 2026

prek 0.4.5 Homebrew/homebrew-core#288054

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Codecov Report

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prek-ci-bot Bot commented Jun 6, 2026

📦 Cargo Bloat Comparison

Head Branch Results

Base Branch Results

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prek-ci-bot Bot commented Jun 6, 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 Jun 6, 2026 •

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codecov Bot commented Jun 6, 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`