Create merge request from email

* new merge request can be created by sending an email to the specific
email address (similar to creating issues by email)
* for the first iteration, source branch must be specified in the mail
subject, other merge request parameters can not be set yet
* user should enable "Receive notifications about your own activity" in
user settings to receive a notification about created merge request

Part of #32878

2 files changed, 12 insertions, 2 deletions

diff --git a/app/services/merge_requests/build_service.rb b/app/services/merge_requests/build_service.rb
index c2fb01466df..9622a5c5462 100644
--- a/app/services/merge_requests/build_service.rb
+++ b/app/services/merge_requests/build_service.rb
@@ -10,8 +10,12 @@ module MergeRequests
       merge_request.target_branch   = find_target_branch
       merge_request.can_be_created  = branches_valid?
 
-      compare_branches if branches_present?
-      assign_title_and_description if merge_request.can_be_created
+      # compare branches only if branches are valid, otherwise
+      # compare_branches may raise an error
+      if merge_request.can_be_created
+        compare_branches
+        assign_title_and_description
+      end
 
       merge_request
     end
diff --git a/app/services/merge_requests/create_service.rb b/app/services/merge_requests/create_service.rb
index 820709583fa..49cf534dc0d 100644
--- a/app/services/merge_requests/create_service.rb
+++ b/app/services/merge_requests/create_service.rb
@@ -35,6 +35,12 @@ module MergeRequests
       super
     end
 
+    # expose issuable create method so it can be called from email
+    # handler CreateMergeRequestHandler
+    def create(merge_request)
+      super
+    end
+
     private
 
     def update_merge_requests_head_pipeline(merge_request)