Can't make use of workflow environment variable in github action from marketplace (through build matrix) - mongodb

Question

I'm trying to make use of a workflow environment variable in a marketplace action, using a build matrix but it's not working for some reason.
I basically want to define the database versions just once to avoid repeating them in multiple place in my workflow.
Here's my workflow (minimal reproducible example):
name: dummy
on:
pull_request:
env:
MONGODB_3_6: 3.6.13
MONGODB_4_0: 4.0.13
jobs:
test:
runs-on: ubuntu-latest
strategy:
matrix:
MONGODB: [$MONGODB_4_0, $MONGODB_3_6]
steps:
- uses: actions/checkout#v2
- name: Start MongoDB
uses: supercharge/mongodb-github-action#1.3.0
with:
mongodb-version: ${{ matrix.MONGODB }}
And it's failing with the error below, as if the MONGODB_4_0 wasn't defined.
Interesting fact, without the strategy matrix, I'm able to make it work using the env context(doc):
- name: Start MongoDB
uses: supercharge/mongodb-github-action#1.3.0
with:
mongodb-version: ${{ env.MONGODB_4_0 }}

Answer 1

UPDATED: according tests and comments, I think matrix can't take environment variables and/or dynamic values.
so the best way will be :
matrix:
MONGODB: [3.6.13, 4.0.13]
As #max said you can use a variable for your workflow, so I guess your matrix should be wrong, maybe you can try like that :
MONGODB: [${{ env.MONGODB_4_0 }}, ${{ env.MONGODB_3_6 }}]
You have only one job (test) so you can define your env variables at the job level also.
Variables will be accessible for all the job :
jobs:
test:
runs-on: ubuntu-latest
env:
MONGODB_3_6: 3.6.13
MONGODB_4_0: 4.0.13
For further information : github doc