Managing Local Changes with Mercurial Queues

Repository Management Problem

gem5 users typically opt to freeze their repository at a particular changeset when starting a new research project. This approach has several downsides:

• It discourages users from contributing back any useful changes they may develop.
• If a useful change is added upstream, it's a long, tedious process to update.

If a user chooses to keep their local repository up-to-date with the source tree they typically use named branches and merge any upstream changes into their branches. This approach also has its downsides:

• If any local change needs to be updated, it requires a separate commit.
• If you have several small, unrelated changes separate branches must be maintained.
• Upstream changes must be merged into the local branches.

A powerful tool that overcomes these problems is the mercurial queue extension.

Mercurial Queues

The mercurial queue extension is a powerful tool that allows you to:

• Manage small changes easily as a set of well-defined patches.
• Edit previous patches without having a new commit.
• Keep your local changes cleanly separated from upstream changes.

Example Mercurial Queue Use

Enable the MQ extension

To enable the mercurial queue extension, simply add the following to your .hgrc file:

[extensions]
hgext.mq =

Simple workflow with MQs

Here is a simple example outlining basic MQ usage:

1. clone a clean copy of gem5

hg clone http://repo.gem5.org/gem5