When creating a new commit, I would like to grab some information from the environment and generate a stub commit message. In my particular case, I want to prefix the message with the last part of the branch name - which happens to be our JIRA number. Having the number in the commit msg makes tracking and reviewing much easier, and auto-generating it makes happy programmers.

Workflow:

• Press commit button
  new: * System calls a generate hook, similar to prepare-commit-msg which generates a file somewhere
  new: * System picks up this file and injects it into commit msg textbox
• User fills in commit message and commits as now.