Add Ubuntu get_related_branch_from_repo (#82)

Signed-off-by: EduPonz <eduardoponz@eprosima.com>

README.md

@@ -150,6 +150,9 @@ For more information about versioning handle of this project, check following [f
 
 - [setup_cmake](ubuntu/setup_cmake/action.yml)
   - Set a specific CMake version
+
+- [get_related_branch_from_repo](ubuntu/get_related_branch_from_repo/action.yml)
+  - Get the related branch from a remote repository.
 ---
 
 ### macOS

ubuntu/get_related_branch_from_repo/action.yml

@@ -0,0 +1,112 @@
+name: get_related_branch_from_repo
+description: >
+  Get the related branch from a remote repository.
+
+  In case the event triggering the workflow is a "pull_request", the branch deduction is as follows:
+
+    1. The action will look for the PR's source branch in the remote repository.
+    2. If the PR's source branch is not found, the action will look for the PR's base branch in the remote repository.
+    3. If the PR's base branch is not found, the action will look for the fallback branch in the remote repository.
+    4. If the fallback branch is not found, the action will fail.
+
+  In case the event triggering the workflow is not a "pull_request", the action will look for the fallback branch in the remote repository, and fail if it is not found.
+
+inputs:
+
+  remote_repository:
+    description: >
+      The remote repository from which to get the related branch.
+      Format: owner/repo (e.g.: eProsima/Fast-DDS).
+    required: true
+
+  fallback_branch:
+    description: >
+      The branch to use if no candidate branch can be found in the remote repository.
+      This is the only branch that is checked for existence in the remote repository in events other that "pull_request".
+    required: true
+
+outputs:
+  deduced_branch:
+    description: "Deduced branch"
+    value: ${{ steps.deduce_branch.outputs.deduced_branch }}
+
+runs:
+  using: composite
+  steps:
+
+    - name: Get related branch from remote repository
+      id: deduce_branch
+      run: |
+
+        # Function to check if a branch exists in a remote repository
+        # Usage: branch_exists <repository_url> <branch_name>
+        #
+        # Arguments:
+        #   - repository_url: The URL of the remote repository
+        #   - branch_name: The name of the branch to check
+        #
+        # Returns: "true" if the branch exists, "false" otherwise
+        function branch_exists ()
+        {
+          ret="false";
+
+          if [[ $(git ls-remote --heads ${1} ${2} | wc -l) != 0 ]]
+          then
+            ret="true"
+          fi
+
+          echo "$ret";
+        }
+
+        # Start by assuming we will fail
+        exit_code=1
+
+        remote_repo=https://github.com/${{ inputs.remote_repository }}.git
+        result_branch=${{ inputs.fallback_branch }}
+
+        # This is a PR event -> deduce which branch to use
+        if [[ ${{ github.event_name }} == "pull_request" ]]
+        then
+          # Attempt to use PR's source branch
+          if [[ $(branch_exists ${remote_repo} ${{ github.head_ref }}) == "true" ]]
+          then
+            result_branch=${{ github.head_ref }}
+            exit_code=0
+          fi
+
+          # Attempt to use PR's base branch
+          if [ ${exit_code} == "1" ] && [ $(branch_exists ${remote_repo} ${{ github.base_ref }}) == "true" ]
+          then
+            result_branch=${{ github.base_ref }}
+            exit_code=0
+          fi
+
+          # Attempt to use fallback branch, which will most likely be the base anyways.
+          # This is just in case the PR was to an intermediate branch
+          if [ ${exit_code} == "1" ] && [ $(branch_exists ${remote_repo} ${{ inputs.fallback_branch }}) == "true" ]
+          then
+            result_branch=${{ inputs.fallback_branch }}
+            exit_code=0
+          fi
+
+        # This is not a PR event -> check if fallback branch exists in the remote repository
+        else
+          if [[ $(branch_exists ${remote_repo} ${{ inputs.fallback_branch }}) == "true" ]]
+          then
+            result_branch=${{ inputs.fallback_branch }}
+            exit_code=0
+          fi
+        fi
+
+        # Set output if some deduced branch was found
+        if [[ ${exit_code} == "0" ]]
+        then
+          echo "Using deduced branch '${result_branch}' for ${remote_repo} repository"
+          echo "deduced_branch=${result_branch}" >> $GITHUB_OUTPUT
+        else
+          echo "No deduced branch found for ${remote_repo} repository"
+        fi
+
+        exit ${exit_code}
+
+      shell: bash

versions.md

@@ -24,6 +24,8 @@ The [Forthcoming](#forthcoming) section includes those features added in `main`
 
 The upcoming release will include the following **features**:
 
+- New Ubuntu `get_related_branch_from_repo` action to get the related branch from a remote repository.
+
 ## v0.14.0
 
 - New `add_labels` action to add labels to a pull request.