ruby: put resolved Ruby's bin dir on $PATH for gem invocations

[xiaoyanli-lyft]

Summary

build_gemspec, resolve_gems, install_single_gem, and install_gems_sequential in crates/prek/src/languages/ruby/gem.rs all spawn <ruby> -S gem .... Ruby's -S flag searches $PATH for the named script.

The rv-ruby tarballs that prek auto-downloads ship gem next to ruby in the same bin/ directory, but prek wasn't putting that directory on $PATH for these child commands. In environments without a system Ruby on PATH (e.g. a vanilla Docker image / CI container), the -S lookup fails and Ruby aborts with:

/<PREK_HOME>/tools/ruby/<version>/bin/ruby: No such file or directory -- gem (LoadError)

The first place this trips is build_gemspec (called from Ruby::install before install_gems), so the user-visible failure is Failed to install hook ...: Failed to build gemspecs. Once that's worked around, gem install --explain would fail identically — same root cause for all four call sites.

This is distinct from #2006 / #2017, which fixed missing gems/bin/ruby shim used at hook run time. The bug here is at hook install time and is not mitigated by 0.3.11 (gem.rs is unchanged across v0.3.10..v0.3.11).

Reproduction repo / context: filed as a separate issue with the full repro alongside this PR.

Fix

Prepend the resolved Ruby's bin dir to $PATH for every ruby -S gem invocation:

• New ruby_path_env(&RubyResult) -> Result<OsString> helper that uses prek_consts::prepend_paths (same helper used by Ruby::run).
• gem_env now takes &RubyResult in addition to gem_home and sets PATH alongside the existing GEM_HOME / BUNDLE_* / MAKEFLAGS env. Returns Result so the prepend_paths join error can propagate (vanishingly rare in practice).
• build_gemspec doesn't have a GEM_HOME to set so it doesn't use gem_env, but it sets PATH directly via the same helper.

Test plan

• cargo fmt --check -p prek — clean
• cargo clippy -p prek --all-targets -- -D warnings — clean
• cargo test -p prek --bin prek — 400 passed; 0 failed (existing unit tests, including all five languages::ruby::gem::tests::*)
• New integration test: languages::ruby::auto_download_gem_install_without_gem_on_path (CI-only, mirrors the existing auto_download gating). It:
  • pins language_version: '3.2.9' to force prek to auto-download Ruby via rv-ruby (and asserts a tools/ruby/3.2.9* directory exists after the run);
  • drops a .gemspec into the local repo so build_gemspec runs;
  • sets additional_dependencies: ["webrick"] so resolve_gems (gem install --explain) and install_single_gem (gem install) run;
  • scrubs ruby and gem from $PATH via the existing remove_bin_from_path helper, so ruby -S gem ... only resolves if the resolved Ruby's bin dir is prepended (i.e. the test would have failed before this fix with the LoadError quoted above).

The pre-existing auto_download test only ran ruby --version and never hit gem; gemspec_workflow used language_version: system and so picked gem up from the system PATH. The new test combines auto-download + gem operations + scrubbed PATH to lock the regression in.

Manual verification of the failure mode (without this fix)

In a container with no system Ruby:

default_language_version:
    ruby: 3.2.1
repos:
  - repo: https://github.com/jumanjihouse/pre-commit-hooks
    rev: 3.0.0
    hooks:
      - id: rubocop

prek install-hooks
# error: Failed to install hook `rubocop`
#   caused by: Failed to build gemspecs
#   caused by: Command `gem build` exited with an error:
#   /.../tools/ruby/3.2.1/bin/ruby: No such file or directory -- gem (LoadError)

With this patch, prek prepends <ruby_prefix>/bin to $PATH, ruby -S gem resolves, and the install proceeds.

[codecov]

Codecov Report

❌ Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.22%. Comparing base (6b9db86) to head (e2f02fe).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
crates/prek/src/languages/ruby/gem.rs	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2021      +/-   ##
==========================================
+ Coverage   92.19%   92.22%   +0.03%     
==========================================
  Files         117      117              
  Lines       23781    23790       +9     
==========================================
+ Hits        21924    21940      +16     
+ Misses       1857     1850       -7     

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[Copilot]

Pull request overview

Fixes Ruby hook install-time failures when prek uses an auto-downloaded rv-ruby toolchain by ensuring ruby -S gem ... can actually find the bundled gem script (which Ruby locates via $PATH).

Changes:

• Add a ruby_path_env helper to prepend the resolved Ruby toolchain’s bin/ directory to PATH.
• Apply the computed PATH to all ruby -S gem ... invocation sites (including build_gemspec and the shared gem_env helper).

[prek-ci-bot]

📦 Cargo Bloat Comparison

Binary size change: -0.77% (26.0 MiB → 25.8 MiB)

Expand for cargo-bloat output

Head Branch Results

 File  .text     Size             Crate Name
 1.3%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_39_1_aes_gcm_encrypt_avx512
 1.3%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_39_1_aes_gcm_decrypt_avx512
 0.3%   0.7%  84.0KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.7%  82.2KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.2%   0.5%  61.1KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.2%   0.4%  56.8KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.4%  53.3KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.4%  46.8KiB              prek prek::run::{{closure}}
 0.2%   0.3%  41.3KiB              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%  28.0KiB        aws_lc_sys aws_lc_0_39_1_edwards25519_scalarmuldouble_alt
 0.1%   0.2%  28.0KiB             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%  27.6KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2%  27.5KiB        aws_lc_sys aws_lc_0_39_1_edwards25519_scalarmuldouble
 0.1%   0.2%  27.4KiB               std core::ptr::drop_in_place<prek::languages::<impl prek::config::Language>::install::{{closure}}>
 0.1%   0.2%  26.4KiB              prek prek::cli::try_repo::try_repo::{{closure}}
 0.1%   0.2%  22.7KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2%  22.5KiB      serde_saphyr saphyr_parser_bw::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
41.2%  86.3%  10.6MiB                   And 23741 smaller methods. Use -n N to show more.
47.7% 100.0%  12.3MiB                   .text section size, the file size is 25.8MiB

Base Branch Results

 File  .text     Size             Crate Name
 1.2%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_39_1_aes_gcm_encrypt_avx512
 1.2%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_39_1_aes_gcm_decrypt_avx512
 0.3%   0.7%  84.0KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.6%  82.2KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.2%   0.5%  60.9KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.2%   0.4%  56.8KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.4%  53.3KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.4%  46.8KiB              prek prek::run::{{closure}}
 0.2%   0.3%  41.3KiB              prek prek::cli::run::run::run::{{closure}}
 0.1%   0.3%  33.1KiB             prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.1%   0.2%  28.0KiB        aws_lc_sys aws_lc_0_39_1_edwards25519_scalarmuldouble_alt
 0.1%   0.2%  28.0KiB             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%  27.6KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2%  27.5KiB        aws_lc_sys aws_lc_0_39_1_edwards25519_scalarmuldouble
 0.1%   0.2%  27.4KiB               std core::ptr::drop_in_place<prek::languages::<impl prek::config::Language>::install::{{closure}}>
 0.1%   0.2%  26.4KiB              prek prek::cli::try_repo::try_repo::{{closure}}
 0.1%   0.2%  23.0KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2%  22.5KiB      serde_saphyr saphyr_parser_bw::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%  86.4%  10.8MiB                   And 23794 smaller methods. Use -n N to show more.
48.0% 100.0%  12.5MiB                   .text section size, the file size is 26.0MiB

[prek-ci-bot]

⚡️ Hyperfine Benchmarks

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

Environment

• OS: Linux 6.17.0-1010-azure
• CPU: 4 cores
• prek version: prek 0.3.11+9 (7efdd91 2026-04-28)
• 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	2.2 ± 0.1	2.1	2.4	1.02 ± 0.04
prek-head --version	2.2 ± 0.1	2.1	2.5	1.00

prek list

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base list	8.7 ± 0.1	8.5	9.0	1.00
prek-head list	8.7 ± 0.1	8.5	9.6	1.00 ± 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	3.1 ± 0.0	3.0	3.1	1.01 ± 0.02
prek-head validate-config .pre-commit-config.yaml	3.0 ± 0.0	2.9	3.2	1.00

prek sample-config

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base sample-config	2.5 ± 0.0	2.4	2.6	1.00
prek-head sample-config	2.5 ± 0.0	2.4	2.6	1.01 ± 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	142.5 ± 2.3	138.7	147.0	1.01 ± 0.03
prek-head run --all-files	141.4 ± 2.7	137.8	144.8	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run --all-files	141.4 ± 3.4	135.4	146.8	1.01 ± 0.03
prek-head run --all-files	140.2 ± 2.8	135.6	144.5	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	140.0 ± 3.4	133.9	145.9	1.00
prek-head run --all-files	143.1 ± 15.5	135.0	247.5	1.02 ± 0.11

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	20.3 ± 0.4	19.7	21.4	1.00
prek-head run trailing-whitespace --all-files	20.6 ± 1.6	19.4	25.7	1.02 ± 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	26.8 ± 2.1	23.6	31.2	1.00 ± 0.12
prek-head run end-of-file-fixer --all-files	26.7 ± 2.3	23.2	30.7	1.00

prek run check-json --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-json --all-files	11.8 ± 0.5	11.3	14.0	1.04 ± 0.06
prek-head run check-json --all-files	11.4 ± 0.4	10.7	12.1	1.00

prek run check-yaml --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-yaml --all-files	11.0 ± 0.4	10.7	12.9	1.02 ± 0.04
prek-head run check-yaml --all-files	10.8 ± 0.1	10.7	11.1	1.00

prek run check-toml --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-toml --all-files	11.0 ± 0.3	10.5	11.6	1.01 ± 0.03
prek-head run check-toml --all-files	11.0 ± 0.2	10.6	11.5	1.00

prek run check-xml --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run check-xml --all-files	10.9 ± 0.2	10.5	11.2	1.00
prek-head run check-xml --all-files	10.9 ± 0.2	10.4	11.5	1.00 ± 0.03

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run detect-private-key --all-files	17.2 ± 1.4	15.2	19.8	1.00 ± 0.12
prek-head run detect-private-key --all-files	17.2 ± 1.5	15.0	20.3	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	21.8 ± 1.8	19.4	25.3	1.01 ± 0.12
prek-head run fix-byte-order-marker --all-files	21.5 ± 1.8	19.1	25.5	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	4.5 ± 0.1	4.4	4.6	1.00
prek-head install-hooks	4.5 ± 0.1	4.4	4.6	1.00 ± 0.02

prek install-hooks (warm - with cache)

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base install-hooks	4.4 ± 0.1	4.4	4.5	1.00
prek-head install-hooks	4.5 ± 0.0	4.4	4.5	1.01 ± 0.02

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	47.9 ± 0.9	46.4	49.5	1.00 ± 0.02
prek-head run	47.9 ± 0.7	46.4	48.8	1.00

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

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run --files '*.json'	8.1 ± 0.1	7.9	8.2	1.01 ± 0.01
prek-head run --files '*.json'	8.0 ± 0.1	7.9	8.1	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	13.2 ± 0.8	12.4	14.6	1.04 ± 0.06
prek-head run --dry-run --all-files	12.7 ± 0.2	12.4	13.1	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	13.0 ± 0.1	12.8	13.2	1.03 ± 0.02
prek-head run check-hooks-apply --all-files	12.7 ± 0.1	12.5	13.1	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 ± 0.1	11.2	11.6	1.00
prek-head run check-useless-excludes --all-files	11.4 ± 0.1	11.2	11.5	1.00 ± 0.01

prek run identity --all-files

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
prek-base run identity --all-files	9.9 ± 0.1	9.7	10.0	1.00
prek-head run identity --all-files	9.9 ± 0.1	9.7	10.0	1.00 ± 0.01

[Copilot]

Pull request overview

This PR fixes Ruby hook install-time failures when prek auto-downloads Ruby (rv-ruby) but the parent process PATH does not include a gem executable, by ensuring the resolved Ruby’s bin/ directory is on PATH for all ruby -S gem ... invocations.

Changes:

• Add a helper to compute a PATH value with the resolved Ruby’s bin/ prepended, and apply it to all ruby -S gem ... call sites during gemspec build / dependency resolution / gem install.
• Adjust gem environment setup (gem_env) to set PATH (in addition to GEM_HOME and bundler-related vars) and propagate join errors.
• Add an integration regression test that scrubs ruby/gem from PATH and verifies hook installation still succeeds when Ruby is auto-downloaded.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
crates/prek/src/languages/ruby/gem.rs	Ensures ruby -S gem can locate the bundled gem script by prepending the resolved Ruby bin/ dir to PATH for install-time gem operations.
crates/prek/tests/languages/ruby.rs	Adds a CI-only regression test covering auto-downloaded Ruby + gem operations with ruby/gem removed from PATH.

[Copilot]

Pull request overview

This PR fixes Ruby hook install-time failures when prek auto-downloads Ruby (rv-ruby) in environments where no system ruby/gem exists on PATH, by ensuring ruby -S gem ... can locate the gem script shipped alongside the resolved Ruby interpreter.

Changes:

• Prepend the resolved Ruby toolchain’s bin/ directory to PATH for all ruby -S gem ... invocations during gemspec build / gem resolution / gem installs.
• Refactor gem install environment setup to propagate PATH join errors via Result.
• Add a CI-only integration regression test that scrubs ruby and gem from PATH while exercising gemspec build + dependency install.

Reviewed changes

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

File	Description
crates/prek/src/languages/ruby/gem.rs	Adds a helper to build a PATH with the resolved Ruby bin/ prepended and applies it to all gem-related ruby -S subprocesses.
crates/prek/tests/languages/ruby.rs	Adds an integration regression test covering auto-downloaded Ruby gem operations when ruby/gem are absent from PATH.

[j178]

Thanks!