Working with checkpoints

There are times that my workflow involves a lot of small and consecutive commits. Commits that their message does not really matter since I will squash them into one that describes my work.

An example is when TDDing a certain functionality. In that case I usually write the test, make it pass and finally make a commit.

Why am I doing that? I see it like small checkpoints. I conclude a part of the functionality so I save it. This helps in restoring my code back to last point that I was happy with its state.

One commit

When I first started working this way I was making a distinct checkpoint for each part. Soon enough I realized that these commits didn’t provide any value. I was making them quick for just saving the code and their message was something like save or checkpoint or t.

So instead of doing this and having to squash lots of commits I started using amend. One commit for the first checkpoint and amend for the rest of them. This way, when I’m finished, I rename the HEAD of the branch to something descriptive and move on.

Lots of steps for one commit

I write my code using an IDE (Android Studio or Intellij IDEA) but when it comes to git I move to a terminal.

This means that for committing I have to (1) move to the terminal, (2) make the proper commit/amend and (3) move back to the IDE. Three steps for one save!

Alt + P

So I decided to fix it.

First the bash script that makes the commit:

	#!/bin/bash

	CHECKPOINT="checkpoint"

	git add .

	if [[ "$(git log –format=%B -n 1 HEAD \| cat)" == "$CHECKPOINT" ]]; then
	git commit –amend –no-edit
	else
	git commit -m"$CHECKPOINT"
	fi

view raw checkpoint.sh hosted with ❤ by GitHub

A simple script that either makes a commit with the message checkpoint or amends the staged changes.

Second the import of this script to the IDE:

The Intellij platform provides a functionality called External Tools:
– Go to Settings -> Tools -> External Tools and click on the add button.
– Set the path of your script where it says Program .
– Disable the Open console for tool output if you don’t want to see the result of your script.

At this point you can either use checkpoint as an action (double shift, type checkpoint) or you can go a step further and create a keyboard shortcut:

Go to Settings -> Keymap -> External Tools -> Right click on the script -> Add Keyboard shortcut.

So now every time I want to create a checkpoint I simple press `Alt + P` and continue working without moving from one program to another!

kscript from docker

This is one of those cases that you go down the rabbit hole and end up doing ten different things before the one that you initially wanted to!

My original intention was to try out kscript. What I ended up doing is learning about dockerfiles, building images and trying to run .kts files without having kscript, or kotlin, installed locally in my machine!

The result

A github repository that you can clone, run the install script and have a kscript executable that works as described here.

Why?

I wanted to play with kscript but did not want to install it on my machine. I don’t like bloating my OS by having libraries and software that might not be used often.

How?

Having everything installed in a docker image and use containers to play with kscript was a one way street for what I wanted to achieve.

Dockerfile

It was my first dockerfile but there are tons of tutorials that helped me out. I ended up using alpine, installing java through its repositories, sdkman using its installation guide and kotlin, kscript through sdkman!

Finally, kscript was added as the image’s entry point which means that every time a container is being run kscript will be the first command that gets executed.

And it worked for the most parts. By executing

docker run –rm -i kscript <params>
rm to remove the container after its done, -i to have the script’s output passed to the terminal

I was able to use kscript as described in its repository, except for the case of having a .kts file!

kscript-router.sh

For the case of a .kts file what turned out to solve my problem was to pass the file’s entire content. And this is part of what kscript-router.sh does. It checks if the first parameter is a .kts file and if so it passes its contents to the container. In every other case it passes all given parameters directly to the container.

install.sh

To tie everything together I added a script that creates the image, adds the router script to the user’s path and creates an alias, named kscript, for executing the router.

kscript-from-docker

Cherry pick all the commits from a merged branch

I recently had to revert an entire feature and create a new branch that would be merged in the future. In git terms, I had to revert my merged branch, create a new one and cherry pick the reverted commits to it.

I’ve been working with git for years but up until now I never had to revert a commit, let alone an entire branch. Turns out reverting is quite simple and can be done in a single command but cherry-picking all the branch’s commits is a repeatable and tedious task since we need to copy each commit, create a string out of them and give it to cherry-pick.

What I wanted was a way to give git the merge commit and let it figure out which commits to cherry-pick. For example, in the case described below:

I would like to cherry-pick all five commits edaa436, 5d48f23, a8f2b4d, 63f2f4e, 1dc3f6a by just providing to git the commit f51c08c.

I had already done a “custom” git-alias so I figured I could do something similar and create cherry-grab: git cherry-grab f51c08c

commit^

Two things helped in creating cherry-grab and the first one is the ^ suffix that one of its usages is to get the commit’s parent. So if we run git show edaa436^ git will translate it to git show 84f8f45.

In our case where the commit is the result of a merge we can specify which of the two parents we want. f51c08c^1 will be translated to 84f8f45 and f51c08c^2 to 1dc3f6a (in a similar way if we need the nth parent we request it by using ^n).

git rev-list <commit>

The second thing was rev-list which returns a list with all the commits that can be reached through the parent “pointer” starting from the provided commit. So if we run git rev-list edaa436 git will return edaa436, 84f8f45 and 55da68d.

Also, rev-list can exclude all commits that are reachable from a given commit as long as we prefix it with the caret (^) symbol. So if we run git rev-list edaa436 ^84f8f45 git will return just edaa436.

cherry-grab

First we need to get the list with all of the branch’s commits. To do that we will use the rev-list command and request all commits starting from the merge-commit’s second parent but exclude all commits that are reachable from the merge-commit’s first parent:

git rev-list 1dc3f6a ^84f8f45

this returns 1dc3f6a, 63f2f4e, a8f2b4d, 5d48f23, edaa436 which are the commits that construct the merged branch.

Then we need to reverse this list so that we can apply each commit in the proper order:

git rev-list 1dc3f6a ^84f8f45 | tac

which returns edaa436, 5d48f23, a8f2b4d, 63f2f4e, 1dc3f6a.

Having the commits in the correct order we just need to pass them to the cherry-pick command to apply their changes:

git rev-list 1dc3f6a ^84f8f45 | tac | xargs git cherry-pick

Finally we need to put in an alias to make it reusable:

	[alias]
	cherry-grab = "!f() { \
	git rev-list $1^2 ^$1^1 \| tac \| xargs git cherry-pick; \
	}; f"

view raw cherry-grab.gitconfig hosted with ❤ by GitHub

Nothing fancy or special, we just wrap the sequence of command with a function and tell git to call that function when ever we use the cherry-grab alias.

In order to make it reusable we replace the parent commits with $1^2 and $1^1 respectively which are translated to the second and first parent of the passed commit.

That’s it:

Git alias with parameters

In the company I work we use the gitflow workflow and in every feature branch we make sure that part of its name is the task’s id which includes a unique number. So what we end up with is something like:

feature/T12345-make-the-app-rock

What I wanted was an easy way to checkout a branch using just the number. I wanted (spoiler: and succeeded) something like this:

git ch 12345

Terminal

Lets see how we can checkout a branch without an alias but by using the task’s number.

Get the branch

We can get the branch by listing all branches (git branch) and then grep for the one that contains the task’s number:

git branch | grep 12345

this will return feature/T12345-make-the-app-rock

Checkout to it

Having a way to get the branch makes the checkout quite easy since we can use bash’s command substitution to execute the above commands and use the result directly in the checkout:

git checkout $(git branch | grep 12345)

Put it in a function

We are now able to checkout the task’s branch but it would be nice if we could change the task’s number more easily. Lets create a function and pass the number as a parameter:

	f() {
	git checkout $(git branch \| grep $1)
	}

view raw f.bash hosted with ❤ by GitHub

The $1 is where the parameter will be used (if we had more parameters we would use $2 for the second, $3 for the third etc).
You can check the function by writing it directly in the terminal. Just make sure that you add newlines (press enter):

The alias

We can change branches easily but once we close the current terminal session we lose everything. Our goal is to have all that in a git alias.

Creating an alias can be achieved either by using git config

git config –global alias.ch checkout

or by doing it manually and adding the alias directly into the .gitconfig file (usually located in the home directory). The file should end up with something like:

	[alias]
	ch = checkout

view raw checkout.gitconfig hosted with ❤ by GitHub

Having just the alias will not help us much. As is, it will work only if we give it the entire branch:

git ch feature/T12345-make-the-app-rock

What we need is a way to connect the function that we created with the alias.

The answer is provided by git itself since it has a way to create aliases that do not execute a git command but an external command:

However, maybe you want to run an external command, rather than a Git subcommand. In that case, you start the command with a ! character. This is useful if you write your own tools that work with a Git repository.
git docs

Following the docs we can change the gitconfig file to look like this (this time the change must be made only manually because our function will need to have newlines):

	[alias]
	ch = "!f() { \
	git checkout $(git branch \| grep $1); \
	}; f"

view raw checkout-with-param.gitconfig hosted with ❤ by GitHub

What will happen when we write git ch 12345 is:

git ch will be replaced with everything inside the "..." (minus the !) ending up with two commands
the first one creates the f function and
the second one calls f with the parameter 12345: f 12345

And that’s it! We now have a git alias that will allow us to checkout a branch using part of its name.

Tag: bash