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Delete subprocess output tempfiles once they are read - #901

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ybai08:fix/close-subprocess-tempfiles
Oct 21, 2026
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sds merged 1 commit into
sds:mainfrom
ybai08:fix/close-subprocess-tempfiles

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@ybai08 ybai08 commented Oct 18, 2026

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Fixes #899

Subprocess.spawn captures the child's stdout and stderr in two Tempfiles and never closes them, so deleting them is left to the garbage collector. On Windows that delete fails with Errno::EACCES when a process left behind by the command (for example the inner ruby.exe of bundle exec rspec) still has the file open, and Ruby prints the finalizer backtrace from the issue on every hook run.

This closes and unlinks both files (Tempfile#close!) in an ensure once the output has been read, so they are gone when spawn returns, including when reading the output raises. As suggested in the issue, this goes through Tempfile#unlink rather than File.unlink, so a delete that Windows refuses is ignored instead of raising.

spawn_detached is unchanged: its child is still running when it returns, so its files are still left to the garbage collector.

Tests

Two examples in spec/overcommit/subprocess_spec.rb record the Tempfiles that spawn creates and check that both are closed and unlinked (Tempfile#path is nil) after it returns: one for a normal run, one where reading the output raises.

The suite was run on macOS with Ruby 4.0.7:

  • bundle exec rspec spec/overcommit/subprocess_spec.rb with lib/overcommit/subprocess.rb reverted to master: 10 examples, 2 failures, both on expected ... closed? to be truthy, got false. With the change: 10 examples, 0 failures.
  • bundle exec rspec: 1657 examples, 4 failures. The same 4 examples fail on master (1655 examples, 4 failures): the git alias #amendment? examples in hook_context/commit_msg_spec.rb:134,140 and hook_context/pre_commit_spec.rb:43,49, which look specific to this machine's Git (Apple Git 2.54).
  • bundle exec rubocop: no offenses.

Not run: anything on Windows, so the Errno::EACCES warning itself was not reproduced; bundle exec overcommit --run.

`Subprocess.spawn` captured the child's stdout and stderr in two
Tempfiles and never closed them, so they were deleted by the garbage
collector whenever it got round to it. On Windows that delete fails with
`Errno::EACCES` if a process left behind by the command still holds the
file open, and Ruby prints a backtrace from the finalizer on every hook
run.

Close and unlink both files in an `ensure` once the output has been
read, so they are removed when `spawn` returns, including when reading
fails.

Fixes sds#899
@sds sds added the bug label Oct 21, 2026
@sds
sds merged commit 4857fcc into sds:main Oct 21, 2026
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sds added a commit to guillaume-d/overcommit that referenced this pull request Nov 10, 2026
* origin/main: (108 commits)
  Remember all previously approved configurations and hooks (sds#665)
  Keep deleted and renamed paths absent while stashing changes (sds#928)
  Document the case-sensitive KtLint hook name (sds#927)
  Update CI actions and pin Ubuntu to clear annotations (sds#926)
  Preserve standard input bytes when forwarding hooks (sds#925)
  Preserve Git-quoted filenames when running all hooks (sds#924)
  Fail when Git cannot enumerate tracked files (sds#923)
  Add note about disabling default hooks (sds#922)
  Close files inspected by LineEndings (sds#921)
  Use Script Host before PowerShell for Windows parent query fallback (sds#920)
  Cache Windows dependency resolution with daily refreshes (sds#919)
  Avoid PowerShell startup for Windows parent command queries (sds#918)
  Avoid repeated CLI startup when preparing integration fixtures (sds#917)
  Allocate more CI runners to Windows with asymmetric sharding (sds#916)
  Shard CI tests across runners and add one required CI check (sds#915)
  Remove EOL Ruby versions from the CI matrix (sds#914)
  Cut CI test time by 68% while preserving the full test matrix (sds#913)
  Cut version 0.75.0 (sds#912)
  Re-enable the full Windows test matrix and fix platform failures (sds#911)
  Read .overcommit.yml as UTF-8 in the hook template (sds#910)
  Update Overcommit logo (sds#907)
  Cut version 0.74.0 (sds#906)
  Keep each worktree's signatures separate (sds#903)
  Recognize amend aliases on macOS (sds#904)
  Exclude files deleted from the working tree from all_files (sds#905)
  Restore the Ruby 2.6-3.1 test checks (sds#902)
  Delete subprocess output tempfiles once they are read (sds#901)
  Stop wrapping commands in cmd.exe on Windows (sds#898)
  Allow URL-only lines to exceed TextWidth body limit (sds#900)
  Cut version 0.73.0 (sds#896)
  Add automated release flow (sds#895)
  Instruct oxfmt not to fail if no files are matched (sds#894)
  Add filetypes to oxc tools (sds#893)
  Add pre commit hook for herb-lint (sds#892)
  Cut version 0.72.0 (sds#891)
  Remove maintainability badge (sds#890)
  Require patched REXML version (sds#889)
  Fix operation state restoration in linked worktrees (sds#887)
  Fail Flay hook when flay crashes instead of silently passing (sds#885)
  Fix Solargraph regexp capture warning (sds#886)
  Cut version 0.71.0 (sds#883)
  Prepare for the new solargraph typecheck format (sds#873)
  Make hook context input reads thread-safe (sds#882)
  Cut version 0.70.0 (sds#880)
  Add oxc pre-commit hooks (sds#879)
  Add Ruby 3.4 and 4.0 to CI matrix (sds#878)
  Cut version 0.69.0 (sds#877)
  Use Etc.nprocessors and handle sandboxed environments (sds#876)
  Cut version 0.68.0 (sds#872)
  Add solargraph pre-commit hook for typechecking (sds#871)
  Update RuboCop in Gemfile to silence a deprecation warning in build (sds#870)
  Cut version 0.67.1
  adds 'set' requirements to diff hook context. (sds#866)
  Add note about unsupported YAML features in `gemfile:` line in default.yml (sds#865)
  Cut version 0.67.0 (sds#864)
  Restore ability to specify "gemfile: false" in config (sds#863)
  Cut version 0.66.0 (sds#861)
  Add `-diff` cli option for running precommit hooks against diffs (sds#860)
  Cut version 0.65.0
  Load bundled gems on expected version (sds#859)
  Update changelog
  Bump rexml to >= 3.3.9 to resolve GHSA-2rxp-v6pw-ch6m (sds#857)
  Expand tildes(~) for hooksPath (sds#853)
  Fix spec compatibility with recent git versions (sds#854)
  Update changelog
  Cut version 0.64.0 (sds#852)
  Add changelog_uri to gemspec (sds#851)
  Support stylelint 16+, which emits messages on stderr (sds#848)
  Add Ruby 3.3 to CI matrix (sds#849)
  Update README with latest requirements (sds#845)
  Fix README badges (sds#844)
  Cut version 0.63.0 (sds#843)
  Add RSpec Hook to PreCommit, Add Applicable files if set (sds#842)
  Fix RuboCop warnings (sds#841)
  [FEATURE] New pre-commit hook: Sorbet (Issue sds#825) (sds#826)
  Green CI PoC (sds#833)
  Revert "Get suite running smoothly again (sds#824)" (sds#840)
  Get suite running smoothly again (sds#824)
  Cut version 0.62.0 (sds#821)
  Allow childprocess 5 (sds#820)
  Update branch for CI from `master` to `main` (sds#819)
  Update RuboCop (sds#818)
  Adding Ruby 3.2 to test matrix (sds#816)
  Cut version 0.61.0 (sds#817)
  fix: local overcommit file merges with existing .overcommit.yml file (sds#815)
  Allow ReplaceBranch to use skip_if (sds#809)
  Cut version 0.60.0 (sds#807)
  Add non ASCII encoding schema support to RailsSchemaUpToDate hook (sds#786)
  Rescue Psych::DisallowedClass in YamlSyntax (sds#805)
  Add optional additional local configuration (sds#799)
  Add MixTest hook (sds#802)
  Add MixFormat hook (sds#801)
  support trailing space in replace_branch's 'replacement_text' config (sds#804)
  Allow overriding Gemfile.lock (sds#796)
  Cut version 0.59.1 (sds#785)
  Revert addition of `--disable-pending-cops` flag to RuboCop (sds#783)
  Revert `Fix encoding of process output under windows` (sds#784)
  Cut version 0.59.0 (sds#780)
  Partial log flushing to make long hooks intuitive (sds#777)
  Fix pronto hooks swallowing generic errors (sds#779)
  ...

# Conflicts:
#	CHANGELOG.md
#	README.md
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Errno::EACCES backtrace printed on every hook run (Windows): Subprocess never closes its Tempfiles

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