Working with stack of patches Quick Reference

Working on Firefox, we strongly recommend working with stack of patches. Patches should be small and could be landed in the order used to push them. This also helps to breakdown the work for different reviewers.

As it can be complex for new comers, this documentation explains the various commands.

In Phabricator, the stack can be seen in the Revision Contents section. The top of the stack (most recent change) is first in the list.

Example:

../_images/example-stack.png

For the overall quick reference guide, see the Firefox Contributors Quick Reference

Visualize the stack

# Mercurial
$ hg wip

# Git
$ git log

Reorder the stack

Sometimes, we want to change the order the patches in the stack. Fortunately, VCS support this easily.

# Mercurial
# Just change the order the patch. The tool should highlight
# potential risks of conflicts.
# Note that ctrl+c works well if used
$ hg histedit

# Git
# In the editor, just move the line below/above
# Remove everything if you want to cancel the operation
$ git rebase -i

Make a change on a patch at the beginning of the stack

In some cases, the reviewer is asking for a change at the bottom of the stack (ie not at the top). So, a simple hg/git commit –amend would not work.

In such case, the following approach can be used:

# Mercurial
# hg will try to guess in which an unambiguous prior commit
$ hg absorb

# if this doesn't work, create a temporary commit
# and merge it using "fold" or "roll"
$ hg histedit

# Git
$ git commit --fixup <hash of the commit>

Removing patches in the stack

To remove a patch in the stack:

# Mercurial
# select "drop" (letter "d")
$ hg histedit

# Git
# Replace "pick" by "drop"
# Or simply remove the line for this commit
$ git rebase -i

Rebasing the stack

As the codebase moves fast, it can be necessary to pull changes from mozilla-central before landing the changes.

# Mercurial
# First, see where your patches are in the stack
$ hg wip
# Then, rebase it:
# If you are a beginner, don't hesitate to add "--dry-run"
$ hg pull
$ hg rebase -b . -d central


# Git
$ git remote update
$ git rebase mozilla/central

Reorganizing the stack in Phabricator

moz-phab reorg [start_rev] [end_rev] allows you to reorganize the stack in Phabricator.

If you’ve changed the local stack by adding, removing or moving the commits around, you need to change the parent/child relation of the revisions in Phabricator.

moz-phab reorg command will compare the stack, display what will be changed and ask for permission before taking any action.