Added more feedback in case branch is already created

Signed-off-by: Jasper Boeijenga <jboeijenga@gmail.com>

plugins/scaffolder-backend-module-gitlab/src/actions/gitlabMergeRequest.ts

@@ -414,20 +414,39 @@ which uses additional API calls in order to detect whether to 'create', 'update'
               execute_filemode: file.executable,
             }));
 
-      let createBranch: boolean;
-      if (actions.length) {
-        createBranch = true;
-      } else {
-        try {
-          await api.Branches.show(repoID, branchName);
-          createBranch = false;
-          ctx.logger.info(
-            `Using existing branch ${branchName} without modification.`,
-          );
-        } catch (e) {
-          createBranch = true;
+      let createBranch = actions.length > 0;
+
+      try {
+        const branch = await api.Branches.show(repoID, branchName);
+        if (createBranch) {
+          const mergeRequests = await api.MergeRequests.all({
+            projectId: repoID,
+            source_branch: branchName,
+          });
+
+          if (mergeRequests.length > 0) {
+            // If an open MR exists, include the MR link in the error message
+            throw new InputError(
+              `The branch creation failed because the branch already exists at: ${branch.web_url}. Additionally, there is a Merge Request for this branch: ${mergeRequests[0].web_url}`,
+            );
+          } else {
+            // If no open MR, just notify about the existing branch
+            throw new InputError(
+              `The branch creation failed because the branch already exists at: ${branch.web_url}.`,
+            );
+          }
         }
+
+        ctx.logger.info(
+          `Using existing branch ${branchName} without modification.`,
+        );
+      } catch (e) {
+        if (e instanceof InputError) {
+          throw e;
+        }
+        createBranch = true;
       }
+
       if (createBranch) {
         try {
           await api.Branches.create(repoID, branchName, String(targetBranch));
@@ -439,6 +458,7 @@ which uses additional API calls in order to detect whether to 'create', 'update'
           );
         }
       }
+
       await ctx.checkpoint({
         key: `commit.to.${repoID}.${branchName}`,
         fn: async () => {