Elixir and Erlang

This guide will help build Elixir and Erlang projects on Semaphore.

Overview

The Elixir and Erlang toolchains are pre-installed in Linux machines. You can switch the active compiler using sem-version.

How to change Elixir versions

Elixir is available on Linux Ubuntu machines and Docker Environments.

On Linux machines use sem-version. For example to switch to v1.16:

sem-version elixir 1.16

Using Docker containers

Semaphore distributes the pre-built semaphoreci:elixir image on the Semaphore Container Registry. Find Dockerfiles to build your custom images in the semaphoreci/docker-images repository.

How to cache Elixir dependencies

The cache tool automatically detects the presence Mix dependencies and compiled code

The first job in the pipeline must cache the dependencies:

checkout
mix local.hex --force
mix local.rebar --force
cache restore
mix do deps.get, compile
cache store

The rest of the jobs can use the cache directly to retrieve dependencies and compiled code:

checkout
cache restore

How to set up test reports

This section explains how to set up test reports (and flaky tests) for Elixir and mix.

1. Add junit-formatter to your mix.exs dependencies

   defp deps do
   [
       # ...
       {:junit_formatter, "~> 3.1", only: [:test]}
   ]
   end

2. Install dependencies

   mix deps.get

3. Extend your config/test.exs

   config :junit_formatter,
   report_dir: "/tmp",
   report_file: "junit.xml", # Save output to "/tmp/junit.xml"
   print_report_file: true, # Adds information about file location when suite finishes
   include_filename?: true, # Include filename and file number for more insights
   include_file_line?: true

4. Extend your tests/test_helper.exs

   ExUnit.configure(formatters: [JUnitFormatter, ExUnit.CLIFormatter])
   ExUnit.start()

5. Create an after_pipeline job with the following command:

   test-results publish /tmp/junit.xml

Example pipeline definition

Test reports in Elixir

- name: Tests
  task:
    prologue:
      commands:
        - checkout
        - mix deps.get
    jobs:
      - name: Elixir Tests
        commands:
          - mix test
    epilogue:
      always:
        commands:
          - test-results publish /tmp/junit.xml

How to change Erlang versions

Elixir is available on Linux Ubuntu machines and Docker Environments.

On Linux machines use sem-version. For example to switch to v25

sem-version erlang 25

How to run Erlang projects

Use earlc to compile an Erlang source code to binary.

For instance, with a source file called hello.erl:

%% Programmer: Mihalis Tsoukalos
%% Date: Friday 21 December 2018

-module(hello).
-export([helloWorld/0]).

helloWorld() -> io:fwrite("hello, world\n").

We can compile and run with:

checkout
sem-version erlang 25
erlc hello.erl
erl -noshell -s hello helloWorld -s init stop