Prek

<!-- Part of the Carbon Language project, under the Apache License v2.0 with LLVM Exceptions. See /LICENSE for license information. SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception -->

prek is the Carbon pre-submit, style, and lint checker. Running it is mandatory before submitting any changes.

Running prek

To run prek on all files:

prek run -a

To validate a specific list of files:

prek run --files <files>

Running prek in a Jujutsu (jj) workspace

If you are working in a Jujutsu workspace, running prek directly will fail because it expects a standard Git repository structure. Instead, use the helper script:

./scripts/jj_prek.sh

This script runs prek on all files that have changed between trunk and your current Jujutsu @ change.

Note that the script always compares against trunk. If your change is based on another bookmark rather than on trunk, the script also checks the files changed by that underlying change, so a reported failure may not be in your own work.

Hooks that rewrite files

Some hooks, notably clang-format and rumdl, fix problems in place rather than only reporting them. When they do, prek reports a failure and exits non-zero even though the tree is now correct.

Re-run prek after any failure that modified files, and treat the second, clean run as the result. Review what it changed: a reflow is expected, but a content change may not be what you intended.

Prek dependency errors

[!TIP] If prek fails with an error about resolving dependencies or security policy, you may be running in a restricted environment where the special-purpose gpkg tool is required. Prefix the command with gpkg, for example: gpkg prek run -a or gpkg ./scripts/jj_prek.sh.