path: root/2022/captions/emacsconf-2022-justl--justl-driving-recipes-within-emacs--sibi-prabakaran--main.vtt

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.