I’m always working with Git. I use it at work, I use it for my personal
projects, I even use it for this site. Git has become a part of my
everyday life. One Git feature that I use quite often is Git-Rebase,
which when invoked with the
-i flag allows you to reorder-,
combine-, and delete commits interactively.
Let’s say you make two commits called ‘Fix various typos’ and ‘Add new blog post’ in that order. Now imagine you found another typo that you forgot to fix in your first commit. You might end up with a history like so:
While for many people this might be fine, I personally find it much more
clean to have the first and third commits merged into one commit, as
they’re two parts of the same task. This is where Git-Rebase comes in.
We can run
git rebase -i HEAD~N where
N is the number of
commits back we want to include, which in this case would be 3. Running
that command will open the following buffer in your text editor. In my
As suggested by the comments added to the bottom of the opened buffer, we can combine the two typo-fixing commits by simply swapping the 2nd- and 3rd lines, and then changing the second typo-fixing commit from a pick to a fixup:
After saving and exiting from your editor, the Git log should now only have two entries, which looks a lot cleaner.
This is fine and all, but it could be better. Specifically, it would be nice if instead of having to navigate to the front of the line, delete the word, and replace it with something new (such as fixup), you could just hit ‘f’ on your keyboard with your cursor on the right line and have it edit the command for you. Along with fixups, it would also be nice to be able to press ‘s’ for squash, ‘r’ for reword, etc.
Seeing as the Git-Rebase interface is line-based with a simple syntax, you could probably easily do this with a regular-expression-based solution. I’m going to use Tree-Sitter though because it’s cooler, and I want to show off how easy it is to use.
Writing The Plugin
The first thing to figure out is where to put the plugin. Seeing as we
only want it active when we’re performing a rebase, we can make use of
after/ftplugin directory. Configurations placed in this
directory will only be applied when working in a buffer whose filetype
corresponds to the filename. By running
:set ft? in a
Git-Rebase buffer we can see that the filetype is ‘
so with all that information we know that we can put our plugin in
The basic skeleton of the plugin is going to look like so:
map function defined here will create a normal-mode
keybinding where pressing the key combination provided as the first
argument will replace the Git-Rebase command of the current line with
the string provided in the second argument. The actual function to
perform this replacement isn’t implemented yet, so in its current state
it will bind these keys to an empty function. We also pass a few
vim.keymap.set; you can read more about these in
:help vim.keymap.set if you’re interested.
The first step to implementing the actual functionality of the plugin is to figure out where we are. We can do this very easily with the Neovim Tree-Sitter API:
ts_utils.get_node_at_cursor() function will return to us the
current node in the Tree-Sitter parse tree that our cursor is located
at. In the case that we don’t have a Tree-Sitter parser available, the
node will be
nil and we can just issue an error.
Before making any more progress, it’s a good idea to make sure you have
a proper understanding of the structure of the
AST. You can view the AST by opening a new
gitrebase buffer and running
:vim.treesitter.inspect_tree(). I implore you to do this
yourself, you’ll learn from it. The AST will end up looking
something like this, followed by a bunch of
As you can see, each line is represented by an operation node which has three child nodes: a command, a label, and a message. You can probably begin to realize now that we’re going to want to get- and modify the command node on the line that our cursor is on.
In the code above we got the node at our cursor, now we need to traverse
the AST to the operation node. We can call the
:parent() method on our node in a loop to traverse up the tree
until we reach our target node. If our cursor isn’t on a valid line
such as on a comment or a blank line we won’t ever hit an operation node
and will instead get
nil, so we need to handle that case too.
Now that we have the operation node, we simply have to get the child
command node (which we know is the first child node), find out where in
the buffer it is, and replace it. We can call the
method on our node to get the first child, and then call the
:range() method on the child to get position in our buffer of
the command node. The
:range() method returns 4 values: the
start row, start column, end row, and end column. We can then pass
these positions to
vim.api.nvim_buf_set_text() to set the text
at the given position.
And that is the entire plugin! In just 28 lines of code (including whitespace) we implemented a plugin using Tree-Sitter to allow you to modify a Git-Rebase command with a single keystroke. The completed product looks like so: