Fix: Panic on overly long filenames instead of silently dropping files

[Copilot]

The Partitions iterator would silently return None when encountering a filename too long to fit in a command line batch, causing all subsequent files to be skipped without warning.

Changes

• crates/prek/src/run.rs:157-174: Replace silent None return with explicit panic including:

  • Problematic filename and byte length
  • Defensive bounds check to prevent unhelpful index out of bounds errors

• crates/prek/src/run.rs:220-358: Add unit tests covering:

  • Normal partitioning behavior
  • Panic on single overly long filename
  • Panic when long filename appears mid-list (critical test ensuring we don't silently skip remaining files)
  • Batch size and CLI length limit enforcement

Error message

thread 'main' panicked at crates/prek/src/run.rs:169:13:
Filename `aaa...aaa` (5001 bytes) is too long to fit in command line

The minimum max_cli_length is 4096 bytes (non-Unix/Windows platforms), making this scenario rare but critical when it occurs.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Potential bug: long command lines might drop files</issue_title>
<issue_description>### Summary

This is theoretical issue I ran into while working on a PR for #1279.

The implementation of Iterator for Partitions in crates/prek/src/run.rs will end the iterator early if command_length + filename_length + 2 > max_length (roughly). Especially if the overly long filename is later in the list, it could result in some files not being checked.

prek/crates/prek/src/run.rs

Lines 121 to 139 in 1856285

	let start_index = self.current_index;
	let mut current_length = self.command_length + 1;
	while self.current_index < self.filenames.len() {
	let filename = self.filenames[self.current_index];
	let length = filename.as_os_str().len() + 1;
	if current_length + length > self.max_cli_length
	|| self.current_index - start_index >= self.max_per_batch
	{
	break;
	}
	current_length += length;
	self.current_index += 1;
	}
	if self.current_index == start_index {
	None

It’s probably not a problem because the shortest maximum CLI length is 4096 bytes (on non-UNIX, non-Windows platforms):

prek/crates/prek/src/run.rs

Lines 64 to 67 in 1856285

	#[cfg(not(any(unix, windows)))]
	{
	1 << 12
	}

Still, maybe it’s worth a panic!? Figured I'd point it out and see if you thought it was worth changing.

Platform

non-UNIX, non-Windows

Version

prek 0.2.25

.pre-commit-config.yaml

No response

Log file

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Potential bug: long command lines might drop files #1284

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.00%. Comparing base (0efd637) to head (07ca875).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1287      +/-   ##
==========================================
+ Coverage   89.94%   90.00%   +0.05%     
==========================================
  Files          80       80              
  Lines       15808    15881      +73     
==========================================
+ Hits        14219    14293      +74     
+ Misses       1589     1588       -1     

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[github-actions]

📦 Cargo Bloat Comparison

Binary size change: +0.00% (16.7 MiB → 16.7 MiB)

Expand for cargo-bloat output

Head Branch Results

 File  .text     Size          Crate Name
 0.7%   1.5% 115.5KiB           prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.6%   1.3% 107.3KiB          prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.3%   0.7%  54.7KiB           prek prek::archive::unpack::{{closure}}
 0.3%   0.7%  52.8KiB             h2 h2::proto::connection::Connection<T,P,B>::poll
 0.2%   0.5%  39.8KiB           prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.5%  39.2KiB          prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.2%   0.5%  39.2KiB           prek prek::run::{{closure}}
 0.2%   0.5%  37.3KiB          hyper hyper::proto::h1::dispatch::Dispatcher<D,Bs,I,T>::poll_loop
 0.2%   0.5%  36.9KiB regex_automata regex_automata::meta::strategy::new
 0.2%   0.5%  36.5KiB           prek prek::workspace::Workspace::discover
 0.2%   0.4%  30.8KiB           std? <core::marker::PhantomData<T> as serde_core::de::DeserializeSeed>::deserialize
 0.2%   0.4%  30.7KiB           prek prek::cli::run::run::run::{{closure}}
 0.2%   0.4%  29.8KiB           prek prek::languages::rust::installer::RustInstaller::install::{{closure}}
 0.2%   0.4%  28.4KiB           prek prek::languages::node::installer::NodeInstaller::install::{{closure}}
 0.2%   0.4%  27.9KiB             h2 h2::proto::connection::DynConnection<B>::recv_frame
 0.2%   0.3%  27.6KiB           prek prek::identify::by_extension::{{closure}}
 0.2%   0.3%  27.3KiB           prek prek::cli::run::run::run_hooks::{{closure}}
 0.2%   0.3%  26.2KiB           prek prek::cli::auto_update::update_repo::{{closure}}
 0.1%   0.3%  25.3KiB           prek prek::main
 0.1%   0.3%  24.7KiB           prek prek::hook::HookBuilder::build::{{closure}}
41.2%  88.5%   6.9MiB                And 10639 smaller methods. Use -n N to show more.
46.5% 100.0%   7.8MiB                .text section size, the file size is 16.7MiB

Base Branch Results

 File  .text     Size          Crate Name
 0.7%   1.4% 114.7KiB           prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.6%   1.3% 107.3KiB          prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.3%   0.7%  54.7KiB           prek prek::archive::unpack::{{closure}}
 0.3%   0.7%  52.8KiB             h2 h2::proto::connection::Connection<T,P,B>::poll
 0.2%   0.5%  39.8KiB           prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.5%  39.2KiB          prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.2%   0.5%  39.2KiB           prek prek::run::{{closure}}
 0.2%   0.5%  37.3KiB          hyper hyper::proto::h1::dispatch::Dispatcher<D,Bs,I,T>::poll_loop
 0.2%   0.5%  36.9KiB regex_automata regex_automata::meta::strategy::new
 0.2%   0.5%  36.5KiB           prek prek::workspace::Workspace::discover
 0.2%   0.4%  30.8KiB           std? <core::marker::PhantomData<T> as serde_core::de::DeserializeSeed>::deserialize
 0.2%   0.4%  30.7KiB           prek prek::cli::run::run::run::{{closure}}
 0.2%   0.4%  29.8KiB           prek prek::languages::rust::installer::RustInstaller::install::{{closure}}
 0.2%   0.4%  28.4KiB           prek prek::languages::node::installer::NodeInstaller::install::{{closure}}
 0.2%   0.4%  27.9KiB             h2 h2::proto::connection::DynConnection<B>::recv_frame
 0.2%   0.3%  27.6KiB           prek prek::identify::by_extension::{{closure}}
 0.2%   0.3%  27.3KiB           prek prek::cli::run::run::run_hooks::{{closure}}
 0.2%   0.3%  26.2KiB           prek prek::cli::auto_update::update_repo::{{closure}}
 0.1%   0.3%  25.3KiB           prek prek::main
 0.1%   0.3%  24.7KiB           prek prek::hook::HookBuilder::build::{{closure}}
41.2%  88.5%   6.9MiB                And 10638 smaller methods. Use -n N to show more.
46.5% 100.0%   7.8MiB                .text section size, the file size is 16.7MiB