In addition to previous answers I wanted to highlight the new options that can also be used with fixup that further differentiate it from using squash.
I am using git version 2.32.1
Lets imagine you are rebasing a branch called my-new-feature onto main.
In order to do this you are doing an interactive rebase using the command git rebase -i main whilst you have the my-new-feature branch checked out.
(If you are using a GUI for git like the OP is using Git Extensions, if they are up to date they should also contain these new options)
Running git rebase -i main opens the following in your editor:
pick 996b0 work in progress
pick 59f3a feature finished
# Rebase b6914..59f3a onto b6914 (2 commands)
#
# Commands:
# p, pick <commit> = use commit
# r, reword <commit> = use commit, but edit the commit message
# e, edit <commit> = use commit, but stop for amending
# s, squash <commit> = use commit, but meld into previous commit
# f, fixup [-C | -c] <commit> = like "squash" but keep only the previous
# commit's log message, unless -C is used, in which case
# keep only this commit's message; -c is same as -C but
# opens the editor
# x, exec <command> = run command (the rest of the line) using shell
# b, break = stop here (continue rebase later with 'git rebase --continue')
# d, drop <commit> = remove commit
# l, label <label> = label current HEAD with a name
# t, reset <label> = reset HEAD to a label
# m, merge [-C <commit> | -c <commit>] <label> [# <oneline>]
# . create a merge commit using the original merge commit's
# . message (or the oneline, if no original merge commit was
# . specified); use -c <commit> to reword the commit message
Note the new -C | -c flag.
s, squash = use commit, but meld into previous commit
f, fixup [-C | -c] = like "squash" but keep only the previous
commit's log message, unless -C is used, in which case
keep only this commit's message; -c is same as -C but
opens the editor
Looking at our 2 commits:
pick 996b0 work in progress
pick 59f3a feature finished
Let's imagine you want to meld them together (something which can be done with squash or fixup) but you want to only keep the helpful commit message of the second commit feature finished.
Using fixup as we have in the past like so:
pick 996b0 work in progress
f 59f3a feature finished
will not do what we want. It will meld the commits together but it will leave us with the work in progress commit message, which is not very helpful.
We could use squash like so:
pick 996b0 work in progress
s 59f3a feature finished
this will open a new editor which will allow you comment out the first commit message manually and persist the feature finished commit message. This does work but it forces you to have an extra manual step; aint nobody got time for dat
This is where the new option we can pass to fixup is super handy.
pick 996b0 work in progress
f -C 59f3a feature finished
This will meld the commits together but discard the work in progress commit message and only keep the feature finished commit message.
These new options make fixup even more powerful and allows you to rely even less on using squash when you don't need to.
rebaseand squash/fixup at the Git docs. – Krystlekrystyna