fix gitlab automatic deletion bug (#1905)

* fix automatic deletion for gitlab

Author: motatoes

ee/backend/controllers/gitlab.go

@@ -197,6 +197,7 @@ func handlePullRequestEvent(gitlabProvider utils.GitlabProvider, payload *gitlab
 	isDraft := payload.ObjectAttributes.WorkInProgress
 	branch := payload.ObjectAttributes.SourceBranch
 	commitSha := payload.ObjectAttributes.LastCommit.ID
+	action := payload.ObjectAttributes.Action
 	//defaultBranch := payload.Repository.DefaultBranch
 	//actor := payload.User.Username
 	//discussionId := ""
@@ -208,6 +209,30 @@ func handlePullRequestEvent(gitlabProvider utils.GitlabProvider, payload *gitlab
 		log.Printf("GetGithubService error: %v", glerr)
 		return fmt.Errorf("error getting ghService to post error comment")
 	}
+
+	// here we check if pr was merged and automatic deletion is enabled, to avoid errors when
+	// pr is merged and the branch does not exist we handle that gracefully
+	if action == "merge" {
+		sourceBranch, _, err := glService.GetBranchName(prNumber)
+		if err != nil {
+			utils.InitCommentReporter(glService, prNumber, fmt.Sprintf(":x: Could not retrieve PR details, error: %v", err))
+			log.Printf("Could not retrieve PR details error: %v", err)
+			return fmt.Errorf("Could not retrieve PR details: %v", err)
+		}
+
+		branchExists, err := glService.CheckBranchExists(sourceBranch)
+		if err != nil {
+			utils.InitCommentReporter(glService, prNumber, fmt.Sprintf(":x: Could not check if branch exists, error: %v", err))
+			log.Printf("Could not check if branch exists, error: %v", err)
+			return fmt.Errorf("Could not check if branch exists: %v", err)
+
+		}
+		if !branchExists {
+			log.Printf("automatic branch deletion is configured, ignoring pr closed event")
+			return nil
+		}
+	}
+
 	comment, err := glService.PublishComment(prNumber, fmt.Sprintf("Report for pull request (%v)", commitSha))
 	discussionId := comment.DiscussionId
 

libs/ci/gitlab/gitlab.go

@@ -301,7 +301,28 @@ func (gitlabService GitLabService) GetApprovals(prNumber int) ([]string, error)
 
 func (gitlabService GitLabService) GetBranchName(prNumber int) (string, string, error) {
 	//TODO implement me
-	return "", "", nil
+	projectId := *gitlabService.Context.ProjectId
+	log.Printf("CheckBranchExists prNumber : %d, projectId: %d \n", prNumber, projectId)
+	options := go_gitlab.GetMergeRequestsOptions{}
+	pr, _, err := gitlabService.Client.MergeRequests.GetMergeRequest(projectId, prNumber, &options)
+	if err != nil {
+		log.Printf("error while getting branch name for pr: %v", err)
+		return "", "", err
+	}
+	return pr.SourceBranch, pr.SHA, nil
+}
+
+func (gitlabService GitLabService) CheckBranchExists(branchName string) (bool, error) {
+	projectId := *gitlabService.Context.ProjectId
+	log.Printf("CheckBranchExists branchName : %v, projectId: %d \n", branchName, projectId)
+	_, resp, err := gitlabService.Client.Branches.GetBranch(projectId, branchName)
+	if err != nil {
+		if resp != nil && resp.StatusCode == 404 {
+			return false, nil
+		}
+		return false, err
+	}
+	return true, nil
 }
 
 func (svc GitLabService) SetOutput(prNumber int, key string, value string) error {