[FEAT] Configure if protected branch rule should apply to admins

- Currently protected branch rules do not apply to admins, however in
some cases (like in the case of Forgejo project) you might also want to
apply these rules to admins to avoid accidental merges.
- Add new option to configure this on a per-rule basis.
- Adds integration tests.
- Resolves #65

services/pull/merge.go

@@ -424,63 +424,64 @@ func IsUserAllowedToMerge(ctx context.Context, pr *issues_model.PullRequest, p a
 	return false, nil
 }
 
-// CheckPullBranchProtections checks whether the PR is ready to be merged (reviews and status checks)
-func CheckPullBranchProtections(ctx context.Context, pr *issues_model.PullRequest, skipProtectedFilesCheck bool) (err error) {
+// CheckPullBranchProtections checks whether the PR is ready to be merged (reviews and status checks).
+// Returns the protected branch rule when `ErrDisallowedToMerge` is returned as error.
+func CheckPullBranchProtections(ctx context.Context, pr *issues_model.PullRequest, skipProtectedFilesCheck bool) (protectedBranchRule *git_model.ProtectedBranch, err error) {
 	if err = pr.LoadBaseRepo(ctx); err != nil {
-		return fmt.Errorf("LoadBaseRepo: %w", err)
+		return nil, fmt.Errorf("LoadBaseRepo: %w", err)
 	}
 
 	pb, err := git_model.GetFirstMatchProtectedBranchRule(ctx, pr.BaseRepoID, pr.BaseBranch)
 	if err != nil {
-		return fmt.Errorf("LoadProtectedBranch: %v", err)
+		return nil, fmt.Errorf("LoadProtectedBranch: %v", err)
 	}
 	if pb == nil {
-		return nil
+		return nil, nil
 	}
 
 	isPass, err := IsPullCommitStatusPass(ctx, pr)
 	if err != nil {
-		return err
+		return nil, err
 	}
 	if !isPass {
-		return models.ErrDisallowedToMerge{
+		return pb, models.ErrDisallowedToMerge{
 			Reason: "Not all required status checks successful",
 		}
 	}
 
 	if !issues_model.HasEnoughApprovals(ctx, pb, pr) {
-		return models.ErrDisallowedToMerge{
+		return pb, models.ErrDisallowedToMerge{
 			Reason: "Does not have enough approvals",
 		}
 	}
 	if issues_model.MergeBlockedByRejectedReview(ctx, pb, pr) {
-		return models.ErrDisallowedToMerge{
+		return pb, models.ErrDisallowedToMerge{
 			Reason: "There are requested changes",
 		}
 	}
 	if issues_model.MergeBlockedByOfficialReviewRequests(ctx, pb, pr) {
-		return models.ErrDisallowedToMerge{
+		return pb, models.ErrDisallowedToMerge{
 			Reason: "There are official review requests",
 		}
 	}
 
 	if issues_model.MergeBlockedByOutdatedBranch(pb, pr) {
-		return models.ErrDisallowedToMerge{
+		return pb, models.ErrDisallowedToMerge{
 			Reason: "The head branch is behind the base branch",
 		}
 	}
 
 	if skipProtectedFilesCheck {
-		return nil
+		return nil, nil
 	}
 
 	if pb.MergeBlockedByProtectedFiles(pr.ChangedProtectedFiles) {
-		return models.ErrDisallowedToMerge{
+		return pb, models.ErrDisallowedToMerge{
 			Reason: "Changed protected files",
 		}
 	}
 
-	return nil
+	return nil, nil
 }
 
 // MergedManually mark pr as merged manually