Do not make the child a session leader by j178 · Pull Request #1586 · j178/prek

j178 · 2026-02-06T10:06:23Z

Closes #1561
Previous fix: #1363

We run subcommands under a PTY so they behave like they do in an interactive terminal (colors, progress bars, etc.). However, this is still a pseudo-terminal and it doesn't necessarily provide a full/accurate terminal environment.

Some libraries (for example Go's termenv) send OSC/CSI queries and wait for a response from the terminal. Our PTY doesn't emulate those responses, so they can block on a timeout if the program insists on probing capabilities.

Previously, we tried to work around this by setting TERM=dumb in the environment, but that caused other issues (for example, some programs (e.g cargo), disable color entirely when they see TERM=dumb, even if the output is actually a terminal that supports color).

We intentionally do not make the child a session leader/foreground process group here. When we did, termenv detected it as foreground and ran OSC probes, which then hung.

We run some commands under a PTY so they behave like they do in an interactive terminal (colors, progress bars, etc.). However, this is still a *pseudo*-terminal and it doesn't necessarily provide a full/accurate terminal environment. Some libraries (for example Go's termenv) send OSC/CSI queries and wait for a response from the terminal. Our PTY doesn't emulate those responses, so they can block on a timeout if the program insists on probing capabilities. Previously, we tried to work around this by setting `TERM=dumb` in the environment, but that caused other issues (for example, some programs (e.g cargo), disable color entirely when they see `TERM=dumb`, even if the output is actually a terminal that supports color). We intentionally do not make the child a session leader/foreground process group here. When we did, termenv detected it as foreground and ran OSC probes, which then hung.

codecov · 2026-02-06T10:07:42Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.65%. Comparing base (3fa9187) to head (a8db079).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1586      +/-   ##
==========================================
- Coverage   91.65%   91.65%   -0.01%     
==========================================
  Files          93       93              
  Lines       18280    18277       -3     
==========================================
- Hits        16755    16751       -4     
- Misses       1525     1526       +1

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Pull request overview

This PR fixes hanging issues with PTY process execution by removing the session leader setup and TERM=dumb environment variable setting. Previously, these workarounds were intended to prevent terminal capability probing issues, but they caused other problems (tools like cargo would disable colors entirely). The new approach simply avoids making the child a session leader, which prevents libraries like Go's termenv from detecting the process as foreground and attempting OSC probes that would hang.

Changes:

Removed session leader setup for PTY child processes to prevent hanging on OSC/CSI capability probes
Removed TERM=dumb environment variable setting that caused color output to be disabled in some tools
Cleaned up unused TERM constant and import
Removed completed TODO comment in list command

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
crates/prek/src/process.rs	Removed session leader setup and TERM=dumb workarounds; updated explanatory comments
crates/prek-consts/src/env_vars.rs	Removed unused TERM constant
crates/prek/src/cli/list.rs	Removed TODO comment that was already completed (full_id already includes project prefix)

crates/prek/src/process.rs

prek-ci-bot · 2026-02-06T10:13:32Z

📦 Cargo Bloat Comparison

Binary size change: +0.00% (23.7 MiB → 23.7 MiB)

Expand for cargo-bloat output

Head Branch Results

 File  .text    Size             Crate Name
 0.3%   0.8% 82.3KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.3%   0.7% 71.1KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.6% 65.6KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.2%   0.5% 51.2KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.5% 50.5KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.4% 41.5KiB              prek prek::cli::run::run::run::{{closure}}
 0.2%   0.4% 38.4KiB              prek prek::run::{{closure}}
 0.1%   0.3% 32.0KiB             prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.1%   0.3% 28.4KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.3% 28.3KiB              prek prek::identify::by_extension::{{closure}}
 0.1%   0.2% 24.8KiB             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% 22.6KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2% 22.1KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2% 22.1KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2% 21.2KiB      clap_builder clap_builder::parser::parser::Parser::get_matches_with
 0.1%   0.2% 20.0KiB   cargo_metadata? <cargo_metadata::_::<impl serde_core::de::Deserialize for cargo_metadata::Package>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map
 0.1%   0.2% 19.5KiB              prek prek::archive::unzip::{{closure}}
 0.1%   0.2% 19.5KiB              prek prek::cli::run::filter::collect_files_from_args::{{closure}}
 0.1%   0.2% 19.3KiB               std core::ptr::drop_in_place<prek::languages::<impl prek::config::Language>::install::{{closure}}>
 0.1%   0.2% 19.2KiB              prek <prek::languages::ruby::ruby::Ruby as prek::languages::LanguageImpl>::install::{{closure}}
38.4%  91.5%  9.1MiB                   And 20917 smaller methods. Use -n N to show more.
41.9% 100.0%  9.9MiB                   .text section size, the file size is 23.7MiB

Base Branch Results

 File  .text    Size             Crate Name
 0.3%   0.8% 81.8KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.3%   0.7% 71.1KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.6% 65.6KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.2%   0.5% 51.2KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.5% 50.5KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.4% 41.4KiB              prek prek::cli::run::run::run::{{closure}}
 0.2%   0.4% 38.4KiB              prek prek::run::{{closure}}
 0.1%   0.3% 31.3KiB             prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.1%   0.3% 28.4KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.3% 28.3KiB              prek prek::identify::by_extension::{{closure}}
 0.1%   0.2% 24.8KiB             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% 22.6KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2% 22.1KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2% 22.1KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2% 21.2KiB      clap_builder clap_builder::parser::parser::Parser::get_matches_with
 0.1%   0.2% 20.0KiB   cargo_metadata? <cargo_metadata::_::<impl serde_core::de::Deserialize for cargo_metadata::Package>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map
 0.1%   0.2% 19.5KiB              prek prek::archive::unzip::{{closure}}
 0.1%   0.2% 19.5KiB              prek prek::cli::run::filter::collect_files_from_args::{{closure}}
 0.1%   0.2% 19.3KiB               std core::ptr::drop_in_place<prek::languages::<impl prek::config::Language>::install::{{closure}}>
 0.1%   0.2% 19.2KiB              prek <prek::languages::ruby::ruby::Ruby as prek::languages::LanguageImpl>::install::{{closure}}
38.4%  91.6%  9.1MiB                   And 20905 smaller methods. Use -n N to show more.
41.9% 100.0%  9.9MiB                   .text section size, the file size is 23.7MiB

Copilot AI review requested due to automatic review settings February 6, 2026 10:06

j178 added the bug Something isn't working label Feb 6, 2026

Copilot started reviewing on behalf of j178 February 6, 2026 10:06 View session

Copilot AI reviewed Feb 6, 2026

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crates/prek/src/process.rs Show resolved Hide resolved

j178 merged commit 72a78ee into master Feb 6, 2026
55 checks passed

j178 deleted the pty branch February 6, 2026 10:17

BrewTestBot mentioned this pull request Feb 6, 2026

prek 0.3.2 Homebrew/homebrew-core#266179

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Do not make the child a session leader#1586

Do not make the child a session leader#1586
j178 merged 1 commit intomasterfrom
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