feat: add option to automatically resolve merge conflicts

Add option to automatically resolve merge conflicts by either accepting the change from `target` (default) or `source`. This behaviour can be defined by specifying the input `resolve_conflicts`.

BREAKING CHANGE: default behaviour for merge conflict changes

Merge conflicts are now resolved using strategy option `ours` by default, forcing conflicts to be auto-resolved cleanly by favoring the `target` version. All non-conflicting changes are still reflected in the merge result.

Set input `resolve_conflicts` to `false` to restore the previous behaviour of failing if any merge conflicts occur.

README.md

@@ -40,6 +40,18 @@ jobs:
           #                 target branch contains changes that are not present in the 
           #                 source branch
           strategy: "merge"
+          # The changes to accept, if strategy `merge` leads to merge conflicts
+          #   Optional
+          #   Default: `target`
+          #   Possible values:
+          #     - `target`: forces conflicts to be auto-resolved cleanly by favoring
+          #                 the target version. All non-conflicting changes are reflected 
+          #                 in the merge result.
+          #     - `source`: forces conflicts to be auto-resolved cleanly by favoring
+          #                 the source version. All non-conflicting changes are reflected 
+          #                 in the merge result.
+          #     - `false`:  `merge` fails if any merge conflicts occur.
+          resolve_conflicts: "theirs"
           # The name to create merge commits with
           #   Required, if strategy `merge` is used
           git_committer_name: ${{ secrets.BOT_GIT_NAME }}

action.yml

@@ -14,6 +14,10 @@ inputs:
     description: 'The strategy to use, if fast-forward is not possible (merge, force, fail)'
     required: false
     default: "merge"
+  resolve_conflicts:
+    description: 'The changes to accept, if strategy `merge` leads to merge conflicts (target, source, false)'
+    required: false
+    default: "theirs"
   git_committer_name:
     description: 'The name to create merge commits with'
     required: false
@@ -45,7 +49,7 @@ runs:
       shell: bash
     - name: Merge ${{ inputs.source }} into ${{ inputs.target }}
       if: inputs.strategy == 'merge'
-      run: git merge ${{ inputs.source }}
+      run: git merge ${{ inputs.source }} ${{ inputs.resolve_conflicts != 'false' && format('--strategy-option {0}', inputs.resolve_conflicts == 'target' && 'ours' || 'theirs') || '' }}
       shell: bash
     - name: Push ${{ inputs.target }}
       if: inputs.strategy == 'merge'