Build tooling with Boot

Juho Teperi / Metosin

ClojuTRE

25.11.2014

Contents

• Example project• Challenges with Leiningen• Solutions using Boot• Summary

Example project

• “(Typical) full-stack Clojure project”• src/clj, backend code• src/cljs• src/cljx, shared code• src/less (or sccs, garden etc.)

Leiningen

• Configuration over code• Great with pure Clojure

projects• Plugins provide additional

tasks

Example project using Lein

• Uses multiple lein plugins• lein cljx auto• lein cljsbuild auto (or figwheel)• lein less auto• lein repl• + unit tests

• Several of these plugins watch for file changes• There are ways to combine all into one

command

Lein, problem #1

• Each lein command starts a JVM• Most commands fork another for the task

• 7 JVMs• much GB• Slow start up

Lein, problem #2

• Plugins are not composable• Descriptive configuration doesn’t help• Each lein plugin implements the file watching

themselves• Each implementation works differently…

Lein, problem #3

• Target directory is in effect a temporary directory

• Lein uberjar• Uses different cljs compiler options• Probably uses same target path

• First thing to try if you have problems: lein clean

:source-paths ["src/clj" "target/generated/clj"] :test-paths ["test/clj"]

:cljsbuild {:builds {:app {:source-paths ["src/cljs" "target/generated/cljs"] :compiler {:output-to "resources/public/js/bootcamp.js" :output-dir "resources/public/js/out" :source-map "resources/public/js/out.js.map" :preamble ["react/react.min.js"] :externs ["react/externs/react.js"] :optimizations :none :pretty-print true}}}}

:profiles {:dev {:plugins [[lein-figwheel "0.1.5-SNAPSHOT"] [lein-cljsbuild "1.0.3"] [com.keminglabs/cljx "0.4.0" :exclusions [org.clojure/clojure]]] :figwheel {:http-server-root "public" :port 3449 :css-dirs ["resources/public/css"]} :cljx {:builds [{:rules :clj :source-paths ["src/cljx"] :output-path "target/generated/clj"} {:rules :cljs :source-paths ["src/cljx"] :output-path "target/generated/cljs"}]}

:cljsbuild {:builds {:app {:source-paths ["dev-src/cljs"]}}}}

+ This is missing e.g. uberjar settings for optimized cljs build

Boot (2)

• Alternative build tool• Boot 1 is the old version• Boot 2 is the new one. It’s a significantly

different as the old one.• Alpha• API changes are imminent etc.• Active development

Boot, solution #1

• “Lein launches multiple JVMs and uses lots of memory”

• All tasks run in the same JVM

• Separate classloaders to prevent deps leaking• Btw. this is the same technique which is used by the app servers

• Disclaimer: I have not tested the memory consumption.

Boot, solution #2

• “Lein tasks are not composable, each plugin implements e.g. file watching themselves”

• Tasks are functions• New tasks are composed from existing tasks

using regular methods: comp• File watching is a task

• Which can be composed together with other tasks

Boot, solution #3

• “Dev and production tasks interfere because they use same directories”

• Tasks create temporary directories as needed• Tasks use Boot API to find sources and publish their results

• Cljx uses API to create temp dir, writes results to the dir...

• Cljs asks for source files using the API -> sources include those written by cljx task

• Processes don’t interfere with each other• running boot package to create production jar shouldn’t leave

around files which break dev build• No need for clean-task

(set-env! :src-paths #{"src/clj" "src/cljs" "src/cljx"} :rsc-paths #{"resources"} :dependencies '[[adzerk/boot-cljs "0.0-2371-27"] [adzerk/boot-cljs-repl "0.1.6"] [adzerk/boot-reload "0.1.6"] [deraen/boot-cljx "0.1.0-SNAPSHOT"] … project deps … ])

(task-options! cljs [:output-to "public/main.js" :source-map true :unified true])

(deftask dev "Start the dev env..." [] (comp (watch) (cljs-repl) (cljx) (start-app) (cljs :optimizations :none) (reload :on-jsload 'saapas.core/main)))

(deftask dev-repl "Connect to the repl started by the dev task." [] (repl :client true))

Global options

● Watch: all following tasks run whenever there is file change.

● cljs-repl, start-app are implemented so that they only run once.

● (start-app is specific to the project)● cljs, cljx no-op if no file changes for them● Reload: Like figwheel. Sends websocket

notifications to browser.

Challenges with Boot

• IDE Support• Editors using nrepl work (fireplace, cider)• Keep project.clj around for Cursive (and

maybe others)• Missing tasks (less, unit testing…)

• boot-cljx was easy to create, so should be the others

Summary

Lein Boot

Task envs Forks new JVMs Multiple classloaders in one JVM

Configuration Configuration over code

Composable functions

Files Static classpath (target, resources)

Tasks create temp dirs

Equivalent JS tool Grunt Gulp, Broccoli

Questions?

Links

• http://boot-clj.com/ • https://github.com/Deraen/saapas• #hoplon @ Freenode