A pre-built binary for cljfmt-runner, created with GraalVM.
bfff0422 — eightytwo 9 months ago
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You can also use your local clone with git send-email.


A pre-built binary for cljfmt-runner, created with GraalVM.

#Quick Start

  1. Download the latest binary from the releases page.

  2. Make the binary executable.

    $ chmod +x cljfmt
  3. Move the downloaded binary to a directory that's on your path, e.g. ~/.local/bin.

  4. Check the formatting of some Clojure code.

    $ pwd
    $ cljfmt --check
    Checked 6 file(s)
    1 file(s) were incorrectly formatted
    --- a/src/clj/hello/core.clj
    +++ b/src/clj/hello/core.clj
    @@ -5,5 +5,5 @@
       (str "Hello, " text "?"))
     (defn -main
    -     ([] (println (say-hello "world")))
    +  ([] (println (say-hello "world")))
       ([text] (println (say-hello text))))
  5. Fix the formatting errors.

    $ cljfmt --fix
    Checked 6 file(s)
    Fixing 1 file(s)

It is also possible to include additional directories for checking:

$ cljfmt --check -- -d dev

#What's This About?

There's a lot of nice Clojure tooling for developers, such as cljfmt, which formats Clojure code idiomatically. These tools are typically run via clj (or lein) and can therefore take seconds to complete. This is because the Clojure code needs to be compiled to Java bytecode which is then executed in a Java virtual machine.

This isn't a huge problem if you are only running cljfmt once or twice. However, if you are going to run cljfmt frequently, such as in a pre-commit hook, then execution time becomes really important.

#How to Create a Native Binary

This project uses the following to create native binaries:

  • clj.native-image - a Clojure program for building GraalVM native images using Clojure Deps and CLI tools.
  • oracle/graalvm-ce - a Docker image with GraalVM installed.
  1. Clone this repository.

    $ git clone https://git.sr.ht/~eightytwo/cljfmt-runner-graalvm
  2. Change to the project directory.

    $ cd cljfmt-runner-graalvm
  3. Build the Docker image.

    $ docker-compose build
    Building graalvm-builder
    Step 1/7 : FROM oracle/graalvm-cd:20.1.0
    Successfully tagged clj-native-graalvm-builder:1.0
  4. Build a native binary of cljfmt-runner.

    $ docker-compose run --rm graalvm-builder

The native binary will be placed in the project directory and will be called cljfmt. Feel free to move this to a directory on your path so you can easily format Clojure code.

#Reducing the Size of the Binary

You might have noticed the binary size is almost 30MB! Using the Ultimate Packer for eXecutables (UPX) you can drastically reduce the size.

  1. Download the latest release of UPX.

  2. Run UPX on the cljfmt binary.

$ ./upx cljfmt
                       Ultimate Packer for eXecutables
                          Copyright (C) 1996 - 2020
UPX 3.96        Markus Oberhumer, Laszlo Molnar & John Reiser   Jan 23rd 2020

        File size         Ratio      Format      Name
   --------------------   ------   -----------   -----------
  30211888 ->   7122948   23.58%   linux/amd64   cljfmt

Packed 1 file.

The packed binary is now 7MB. That's still large, but a 75% reduction in size is certainly a nice improvement!


  • cljfmt: a great tool for developers that helps avoid formatting discussions on pull requests. This project was also a great resource for learning how to deal with command line arguments in Clojure.

  • cljfmt-runner: making it possible to use cljfmt in tools.deps projects.

  • clj.native-image: providing functionality to build GraalVM native images with Clojure Deps and CLI tools. This was also a valuable resource for learning about GraalVM's reflection config which was necessary to resolve a build error. Coincidentally, this discussion was related to a fork of cljfmt-runner for building a native executable.

  • UPX project: making it possible to not have to lug around a 30MB executable.