Github-actions - composer fails with 'sh: git: not found'? - composer-php

Question

I have a wordpress plugin where i'm using composer to define my dependent libaries and github-actions to build the installable package. I plan to publish the vendors folder to a 'build' branch in github so the whole application can be installed.
My composer.json file has this content and works locally
{
"name" : "emeraldjava/bhaa_wordpress_plugin",
"description" : "bhaa_wordpress_plugin",
"type" : "wordpress-plugin",
"require": {
"scribu/scb-framework": "dev-master",
"scribu/lib-posts-to-posts": "dev-master",
"mustache/mustache": "2.12.0",
"league/csv": "^9.1",
"michelf/php-markdown": "^1.8"
},
and my github-actions build.yml file uses 'MilesChou/composer-action' to install the composer env in the docker container
jobs:
build:
runs-on: ubuntu-latest
steps:
- name: Checkout
uses: actions/checkout#v1
- name: Composer install
uses: MilesChou/composer-action/7.3#master
with:
args: install --no-dev
- uses: docker://php:7.3-alpine
- uses: docker://alpine/git:latest
From the build log, I can see that the zip files for these composer artifacts have been downloaded to the cache
36/38: https://codeload.github.com/scribu/wp-scb-framework/legacy.zip/95b23ac342fce16bf5eb8d939ac5a361b94b104b
37/38: https://codeload.github.com/sebastianbergmann/phpunit/legacy.zip/a7834993ddbf4b0ed2c3b2dc1f3b1d093ef910a9
38/38: https://codeload.github.com/scribu/wp-lib-posts-to-posts/legacy.zip/a695438e455587fa228e993d05b4431cde99af1b
Finished: success: 38, skipped: 0, failure: 0, total: 38
The build then failed with this 'sh: git: not found' error
Package operations: 5 installs, 0 updates, 0 removals
- Installing scribu/scb-framework (dev-master 95b23ac): Cloning 95b23ac342
Failed to download scribu/scb-framework from source: Failed to clone https://github.com/scribu/wp-scb-framework.git, git was not found, check that it is installed and in your PATH env.
sh: git: not found
Now trying to download from dist
- Installing scribu/scb-framework (dev-master 95b23ac): Loading from cache
- Installing scribu/lib-posts-to-posts (dev-master a695438): Cloning a695438e45
Failed to download scribu/lib-posts-to-posts from source: Failed to clone https://github.com/scribu/wp-lib-posts-to-posts.git, git was not found, check that it is installed and in your PATH env.
sh: git: not found
Now trying to download from dist
- Installing scribu/lib-posts-to-posts (dev-master a695438): Loading from cache
- Installing mustache/mustache (v2.12.0): Loading from cache
- Installing michelf/php-markdown (1.8.0): Loading from cache
- Installing league/csv (9.4.1): Loading from cache
I'm assuming i need to ensure the docker container had git installed, but it seems odd that composer can access the legacy.zip file, so why it git needed at this stage?
EDIT 1
I guess the quick fix here is a duplicate of this issue, and as the answer below states.
For the sake of completeness, lets assume i can't call 'composer --prefer-dist' how could i ensure the docker container has git available to it?

Answer 1

By default Composer uses dist (zip files) for tagged releases and source (git clone) for branches. Since you're targeting master branch for your dependencies, Composer tries to clone repositories first. You can override this behavior by using --prefer-dist switch:
with:
args: install --prefer-dist --no-dev
--prefer-dist: Reverse of --prefer-source, Composer will install from dist if possible. This can speed up installs substantially on build
servers and other use cases where you typically do not run updates of
the vendors. It is also a way to circumvent problems with git if you
do not have a proper setup.
https://getcomposer.org/doc/03-cli.md#install-i