WEBVTT captioned by sachac
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Hi everyone, I am Sibi Prabakaran
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and welcome to my session on Justl Emacs Mode.
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A bit about me, I have been working
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as a Haskell Engineer
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at FPComplete for the last 4 years.
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I am based out of India.
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I occasionally blog at my website psibi.in
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where you can find more information about me.
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I have been using Emacs
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for more than a decade now.
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I help in the maintenance
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of the Terraform client for LSP mode.
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I have also authored dhall-mode and rego-mode
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which are the major modes
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for the respective languages.
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Before jumping into the demo
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of the Emacs package,
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I would like to give a brief introduction
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about justfiles and what it is.
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I will also try to compare it with Makefiles
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as it takes a lot of inspiration from it.
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What you see currently in the buffer
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is a sample justfile.
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If you have previously used Makefiles,
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you would be able to see
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that there is quite a bit of similarity
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between them.
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Anything that starts with hash
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is a documentation comment.
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You can see that I have the first recipe
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which is named as default.
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So if you run the just executable
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without any arguments,
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by default it is going to run
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the first recipe.
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This recipe's definition
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calls the just command
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in turn, with the two arguments,
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namely --list and --unsorted,
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which basically asks just
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to list down all the recipes
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in an unsorted order.
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Each line of each recipe is executed
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by a fresh shell.
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That pretty much
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is the high level overview
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of getting started to use this tool.
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This tool assumes the presence of a shell
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which is bash in most GNU/Linux systems,
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but you can configure it
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to explicitly use any specific shell
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you have in mind.
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Let me in fact go and try executing
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the first recipe.
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I will first execute it
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without any arguments,
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which will force it to run the first recipe.
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As you can see, it listed all the recipes.
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Now I can actually execute
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a particular recipe
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by passing an explicit recipe name.
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Let me execute the hello recipe now
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which will basically print "hello world".
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It works as expected.
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As you can see, that's all that's required
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to get started with this tool.
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You create a file named justfile
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in a directory, define some recipes
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and then run them
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via the just executable.
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Note that there are
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various other features in justfile.
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You can define variables,
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mark some variables
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to be exported as environment variables,
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have optional parameters
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that can be passed to a recipe.
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You can also set up dependency
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between recipes
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and also write scripts within a recipe
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in a language of your choice.
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I won't be going into the details,
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but I encourage you to go through
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the very helpful manual page
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to learn more about it.
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Also, let me compare it with Makefiles.
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I do think it's kind of unfair
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to compare both the tools
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since make is a build automation tool
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whereas just's goal is a task runner,
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and since just doesn't try to be
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a build system,
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it can avoid the associated complexity
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that comes with the tool like make.
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There is one nice historical fact
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about just.
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The initial version of just
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relied on make command being available,
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so it was basically
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a glorified wrapper around it.
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But it was removed,
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and justfile doesn't have
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that dependency anymore.
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If you are using make as a task runner
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then you would have to use
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something called phony targets.
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I don't want to go into the details,
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but makefiles have good reason
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for why they need something like that.
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Since justfile is not a build system,
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it doesn't have to deal with them.
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The error message
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and user experience of this tool,
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in my opinion, is better.
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To show you a concrete example,
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justfile errors out by default
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if you have duplicate recipes.
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This is in contrast with make
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where I believe it prints out
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a warning about it,
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but still executes the target action.
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Justfile also gives you the ability
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to easily create scripts
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written in any language within a recipe.
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My personal opinion is that
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if you are using makefile
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as a task runner,
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you might want to check out justfile
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to see if it will suit your workflow.
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With that, I'll move on to justl.el,
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which is basically an Emacs package
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for driving justfiles.
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I started writing this tool
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around a year ago
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when my usage of justfile increased.
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The objective of the tool
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is to reduce the usage of the CLI
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and drive the execution of the recipes
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natively within the editor.
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Let me take you back to the justfile
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which we saw previously.
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This time we will drive it
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within the editor itself,
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instead of executing commands via vterm
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as done previously.
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So the idea is you either
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open the justfile,
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or any other file in the directory.
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That doesn't matter, actually.
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Once you do that,
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you call the justl command.
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Now as you can see, it lists down
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all the recipes,
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along with the description if present.
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You can move on to different recipes
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by your usual keybinding.
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And for executing a specific recipe,
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you have to press the e keybinding,
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and that will run the recipe
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and show its output
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on a special buffer named *just*
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which is built on top of
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the compilation mode available in Emacs.
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Let me actually try
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executing the hello recipe
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which we previously executed in vterm.
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As you can see,
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it executed the recipe
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and the "hello world" output
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is visible in the just buffer.
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You can also see that there is
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other metadata like
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when it started executing
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and when did it finish executing.
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If a recipe execution fails,
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it will also change the color
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and print the corresponding exit code.
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Let me actually show you
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by modifying the hello recipe
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and making it exit.
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As you can see,
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it clearly indicates the error message now.
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That is a pretty much
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a good high level overview
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of how to execute recipes
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using this Emacs extension.
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If I press the h or the ? key,
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it will display the various ways
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to drive it.
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Now as you can see,
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you can pass various options to it.
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I find the dry run option effective
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whenever I have to print the recipe contents
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without actually executing the recipe.
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There are also various ways to execute it.
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You can use Emacs's eshell to execute it
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by pressing the E keybinding.
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Let me try executing the hello recipe again,
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but this time via Emacs's eshell.
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As you can see now I have an eshell instance
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where it executed the just hello recipe.
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You can also directly
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go to the recipe line
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by pressing the return key.
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So let's say if I want to
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go to the recipe build app
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all I have to do is press the return key
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and it will go to the just file
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with the proper line.
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You can also re-execute the same recipe
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from the output just buffer.
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I find this very helpful
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when iterating on certain things.
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In my day job,
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I often have to work with a Kubernetes cluster,
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and I would have to write
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resource manifest files for applications.
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Having the ability to run the recipes
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while iterating on the project
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is very useful, in my opinion.
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Let me actually show you
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an example of what I am talking about.
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Let me run the build app recipe now,
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which will basically build the manifest
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and print it out.
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Now let me open one of the application files.
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I will open the ingress.yaml file.
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So I have this YAML file which I am working on,
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and I also have this output buffer
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which is basically the output
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of the build app recipe.
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Now I can basically go through this buffer
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and see if everything is alright,
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but I find out that I didn't want
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the hostname to be emacs2022.
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I wanted it to be just emacs.
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I can go and fix it in my YAML file,
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and then I can go on
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to the output buffer
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and basically just re-run the command
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by pressing the g key binding.
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As you can see,
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it executed the same recipe again,
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and I can see that
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the hostname is indeed emacs.
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I find this kind of workflow very convenient
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while I am working on a project.
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Another way of interacting
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with the justl extension
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is by using the interactive function
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justl-exec-recipe-in-dir.
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The use case of this function
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is executing a one-off recipe
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while you are working on something else.
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Let me show you an example of it.
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As you can see, it shows me
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a drop down of various recipes
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available in the justfile.
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You can choose any particular one
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and execute the corresponding recipe.
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In this case, I will choose
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the build-app recipe,
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and we will get the output
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in the *just* buffer
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which should be similar
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to what we saw previously.
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So this was a quick introduction
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to what justfile is
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and how to drive them within Emacs.
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Hopefully it was helpful
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and it would encourage you
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to use justfiles in your workflow.
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Thank you for allowing me to present.
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I am available in IRC
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if you have any questions.
