Reduce allocations during config loading

[j178]

Borrow configuration mapping keys when possible, while retaining owned keys when YAML decoding requires it.

Also avoid formatting unused-key paths and collecting mutable revisions unless those values are needed.

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[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.34%. Comparing base (cd9478f) to head (8fa13ca).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
crates/prek/src/config.rs	95.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2362      +/-   ##
==========================================
+ Coverage   93.33%   93.34%   +0.01%     
==========================================
  Files         129      129              
  Lines       27475    27472       -3     
==========================================
+ Hits        25643    25644       +1     
+ Misses       1832     1828       -4     

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[prek-ci-bot]

📦 Cargo Bloat Comparison

Binary size change: +0.00% (29.1 MiB → 29.1 MiB)

Expand for cargo-bloat output

Head Branch Results

 File  .text     Size             Crate Name
 1.1%   2.3% 332.0KiB        aws_lc_sys aws_lc_0_42_0_aes_gcm_encrypt_avx512
 1.1%   2.3% 332.0KiB        aws_lc_sys aws_lc_0_42_0_aes_gcm_decrypt_avx512
 0.3%   0.6%  79.0KiB              prek <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.2%   0.4%  58.0KiB              prek <<prek::config::Config as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<<serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
 0.2%   0.3%  49.4KiB annotate_snippets annotate_snippets::renderer::render::render
 0.1%   0.3%  42.7KiB              prek prek::cli::run::run::run::{closure#0}
 0.1%   0.3%  39.7KiB              prek prek::run::{closure#0}
 0.1%   0.2%  31.9KiB              prek <prek::cli::RunOptions as clap_builder::derive::Args>::augment_args
 0.1%   0.2%  30.1KiB     granit_parser <granit_parser::scanner::Scanner<granit_parser::input::str::StrInput>>::fetch_more_tokens
 0.1%   0.2%  29.3KiB              prek <<prek::config::RemoteHook as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<<serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
 0.1%   0.2%  28.6KiB    cargo_metadata <&mut serde_json::de::Deserializer<serde_json::read::StrRead> as serde_core::de::Deserializer>::deserialize_struct::<<cargo_metadata::Package as serde_core::de::Deserialize>::deserialize::__Visitor>
 0.1%   0.2%  28.0KiB        aws_lc_sys aws_lc_0_42_0_edwards25519_scalarmuldouble_alt
 0.1%   0.2%  27.5KiB        aws_lc_sys aws_lc_0_42_0_edwards25519_scalarmuldouble
 0.1%   0.2%  26.7KiB              prek prek::cli::try_repo::try_repo::{closure#0}
 0.1%   0.2%  25.6KiB              prek <<prek::config::LocalHook as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<<serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
 0.1%   0.2%  25.2KiB              prek <<prek::config::UpdateOptions as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<<serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
 0.1%   0.2%  24.9KiB               xml <xml::reader::parser::PullParser>::dispatch_token
 0.1%   0.2%  24.4KiB              prek prek::cli::update::update::{closure#0}
 0.1%   0.2%  24.3KiB              prek <prek::languages::node::installer::NodeInstaller>::install::{closure#0}
 0.1%   0.2%  24.0KiB     granit_parser <granit_parser::scanner::Scanner<serde_saphyr::de::buffered_input::ReaderInput>>::fetch_more_tokens
42.3%  88.2%  12.3MiB                   And 25704 smaller methods. Use -n N to show more.
47.9% 100.0%  14.0MiB                   .text section size, the file size is 29.1MiB

Base Branch Results

 File  .text     Size             Crate Name
 1.1%   2.3% 332.0KiB        aws_lc_sys aws_lc_0_42_0_aes_gcm_encrypt_avx512
 1.1%   2.3% 332.0KiB        aws_lc_sys aws_lc_0_42_0_aes_gcm_decrypt_avx512
 0.3%   0.6%  79.3KiB              prek <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.2%   0.4%  58.0KiB              prek <<prek::config::Config as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<<serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
 0.2%   0.3%  49.4KiB annotate_snippets annotate_snippets::renderer::render::render
 0.1%   0.3%  40.8KiB              prek prek::cli::run::run::run::{closure#0}
 0.1%   0.3%  39.5KiB              prek prek::run::{closure#0}
 0.1%   0.2%  33.2KiB              prek prek::archive::unpack::<fs_err::tokio::file::File, &std::path::PathBuf>::{closure#0}
 0.1%   0.2%  32.1KiB              prek <prek::cli::RunOptions as clap_builder::derive::Args>::augment_args
 0.1%   0.2%  30.5KiB              prek prek::cli::update::update::{closure#0}
 0.1%   0.2%  30.1KiB     granit_parser <granit_parser::scanner::Scanner<granit_parser::input::str::StrInput>>::fetch_more_tokens
 0.1%   0.2%  29.3KiB              prek <<prek::config::RemoteHook as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<<serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
 0.1%   0.2%  28.6KiB    cargo_metadata <&mut serde_json::de::Deserializer<serde_json::read::StrRead> as serde_core::de::Deserializer>::deserialize_struct::<<cargo_metadata::Package as serde_core::de::Deserialize>::deserialize::__Visitor>
 0.1%   0.2%  28.0KiB        aws_lc_sys aws_lc_0_42_0_edwards25519_scalarmuldouble_alt
 0.1%   0.2%  27.5KiB        aws_lc_sys aws_lc_0_42_0_edwards25519_scalarmuldouble
 0.1%   0.2%  25.8KiB              prek prek::cli::try_repo::try_repo::{closure#0}
 0.1%   0.2%  25.6KiB              prek <<prek::config::LocalHook as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<<serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
 0.1%   0.2%  25.2KiB              prek <<prek::config::UpdateOptions as serde_core::de::Deserialize>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::<<serde_saphyr::de::deserializer::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map::MA>
 0.1%   0.2%  24.9KiB               xml <xml::reader::parser::PullParser>::dispatch_token
 0.1%   0.2%  24.4KiB              prek <prek::languages::node::installer::NodeInstaller>::install::{closure#0}
42.1%  88.0%  12.3MiB                   And 25812 smaller methods. Use -n N to show more.
47.8% 100.0%  13.9MiB                   .text section size, the file size is 29.1MiB

[prek-ci-bot]

⚡️ Hyperfine Benchmarks

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

Environment

• OS: Linux 6.17.0-1020-azure
• CPU: 4 cores
• prek version: prek 0.4.10+6 (7f8a1cc 2026-07-19)
• Rust version: rustc 1.97.1 (8bab26f4f 2026-07-14)
• 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	2.3 ± 0.1	2.2	2.6	1.00 ± 0.05
prek-head --version	2.3 ± 0.1	2.2	2.7	1.00

prek list

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base list	9.4 ± 0.1	9.2	9.6	1.00
prek-head list	9.4 ± 0.2	9.2	10.3	1.01 ± 0.02

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base validate-config .pre-commit-config.yaml	3.3 ± 0.1	3.2	3.4	1.00 ± 0.02
prek-head validate-config .pre-commit-config.yaml	3.3 ± 0.1	3.2	3.4	1.00

prek sample-config

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base sample-config	2.6 ± 0.0	2.5	2.7	1.00
prek-head sample-config	2.6 ± 0.0	2.5	2.7	1.00 ± 0.02

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	73.3 ± 2.6	70.8	79.0	1.02 ± 0.04
prek-head run --all-files	72.0 ± 1.7	69.4	75.0	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run --all-files	74.2 ± 2.7	69.3	78.7	1.00 ± 0.05
prek-head run --all-files	73.9 ± 2.9	69.5	80.1	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	74.6 ± 2.7	70.0	80.7	1.00 ± 0.05
prek-head run --all-files	74.3 ± 2.4	70.7	79.3	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	19.7 ± 0.3	19.0	20.5	1.01 ± 0.02
prek-head run trailing-whitespace --all-files	19.4 ± 0.3	18.9	20.3	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	26.0 ± 2.0	23.5	30.7	1.00
prek-head run end-of-file-fixer --all-files	26.4 ± 2.2	23.4	30.3	1.02 ± 0.12

prek run check-json --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-json --all-files	7.9 ± 0.3	7.6	8.6	1.01 ± 0.05
prek-head run check-json --all-files	7.8 ± 0.3	7.4	8.4	1.00

prek run check-yaml --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-yaml --all-files	7.7 ± 0.1	7.5	8.2	1.01 ± 0.02
prek-head run check-yaml --all-files	7.6 ± 0.1	7.4	8.0	1.00

prek run check-toml --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-toml --all-files	7.8 ± 0.3	7.3	8.2	1.00
prek-head run check-toml --all-files	7.8 ± 0.2	7.4	8.4	1.00 ± 0.04

prek run check-xml --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-xml --all-files	7.7 ± 0.4	7.2	8.9	1.01 ± 0.06
prek-head run check-xml --all-files	7.7 ± 0.2	7.4	8.2	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	13.0 ± 0.9	11.8	14.5	1.00
prek-head run detect-private-key --all-files	13.7 ± 1.4	11.6	17.4	1.05 ± 0.13

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	17.7 ± 0.9	16.4	19.9	1.01 ± 0.06
prek-head run fix-byte-order-marker --all-files	17.6 ± 0.6	16.7	18.9	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	4.6 ± 0.0	4.6	4.7	1.00
prek-head install-hooks	5.1 ± 0.2	4.9	5.4	1.09 ± 0.04

prek install-hooks (warm - with cache)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base install-hooks	4.9 ± 0.1	4.7	5.0	1.03 ± 0.03
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	39.0 ± 0.9	37.7	40.7	1.01 ± 0.04
prek-head run	38.6 ± 1.0	37.3	40.2	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run --files '*.json'	8.3 ± 0.1	8.2	8.4	1.01 ± 0.01
prek-head run --files '*.json'	8.2 ± 0.1	8.1	8.4	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	7.1 ± 0.1	7.0	7.5	1.00 ± 0.02
prek-head run --dry-run --all-files	7.1 ± 0.1	7.0	7.3	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	12.4 ± 0.1	12.2	12.5	1.00
prek-head run check-hooks-apply --all-files	12.5 ± 0.1	12.4	12.7	1.01 ± 0.01

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-useless-excludes --all-files	12.5 ± 0.1	12.4	12.7	1.05 ± 0.10
prek-head run check-useless-excludes --all-files	11.8 ± 1.2	11.0	14.2	1.00

prek run identity --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run identity --all-files	10.5 ± 0.1	10.4	10.7	1.00
prek-head run identity --all-files	42.9 ± 78.8	10.4	299.5	4.09 ± 7.52

⚠️ Warning: Performance regression for prek run identity --all-files: 308.7100% slower

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