It’s a bit of an embarrassment when you submit a review to Gerrit only to have it fail CI checks immediately because of something as simple as a syntax error or pep8 failure that you should have caught yourself before submitting…but you forgot to run your validations before submitting the change.

In many cases you can alleviate this through the use of the git pre-commit hook, which will run every time you commit changes locally. You can have the hook run tox or whatever tool your project uses for validation on every commit. This works okay for simple cases, but if the validation takes more than a couple of seconds the delay can be disruptive to the flow of your work.

What you want is something that stays out of the way while you are working locally, but that will prevent you from submitting something for review that’s going to fail CI immediately. If you are using the git-review tool to interact with Gerrit (and if you’re not, you should be), you’re in luck! The git-review tool supports a pre-review hook that does exactly what we want. git-review looks for hooks in a global location (~/.config/git-review/hooks) and in a per-project location (in .git/hooks/). As with standard Git hooks, the pre-review hook must be executable (i.e., chmod u+x .git/hooks/pre-review).

The pre-review script will be run before attempting to submit your changes to Gerrit. If the script exits successfully, the output is hidden and your changes will be submitted normally. If the hook fails, you will see output along the lines of…

Custom script execution failed.
The following command failed with exit code 1

…followed by the output of the pre-review script.

For my work on the tripleo-quickstart project, the contents of my .git/hooks/pre-review script is as simple as: