There is git submodule , dictionary-jpa, in a public github repository https://github.com/rxue/dictionary-ci-cd
The content of .gitmodules is the following

[submodule "dictionary-jpa"]
    path = dictionary-jpa
    url = [email protected]:rxue/dictionary-jpa.git

On base of this setup, a Github Action is created with the following script

name: Build

on:
push:
branches: [ main ]

jobs:
build:

runs-on: ubuntu-latest
permissions:
  contents: read
  packages: write

steps:
- uses: actions/checkout@v3
- name: Set up JDK 17
  uses: actions/setup-java@v3
  with:
    java-version: '17'
    distribution: 'temurin'
    submodules: recursive
    #settings-path: ${{ github.workspace }} # location for the settings.xml file
- name: List submodule content
  run: |
    ls -al dictionary-jpa
- name: Build submodule
  run: mvn -B compile --file dictionary-jpa/pom.xml

This action is expected to compile the code inside the submodule dictionary-jpa

Problem: Based on the output of the command ls -al dictionary-jpa, the submodule is empty when the action is being executed, and as a result the mvn compile failed since it cannot find the pom.xml and the source code in the src even though the original repository i.e. the submodule has all the needed files

I added the submodules: recursive according to answers from some other similar questions, but it does not work