Merge branch 'fj-62807-not-prefill-target-branch' into 'master'

Avoid filling target branch when unknown and source is default branch

Closes #62807

See merge request gitlab-org/gitlab-ce!32701

2 files changed, 18 insertions, 5 deletions

diff --git a/app/services/merge_requests/build_service.rb b/app/services/merge_requests/build_service.rb
index 308a3a10d1a..88ed0c3ef4c 100644
--- a/app/services/merge_requests/build_service.rb
+++ b/app/services/merge_requests/build_service.rb
@@ -33,7 +33,8 @@ module MergeRequests
       merge_request.assign_attributes(params.to_h.compact)
 
       merge_request.compare_commits = []
-      merge_request.target_branch = find_target_branch
+      set_merge_request_target_branch
+
       merge_request.can_be_created = projects_and_branches_valid?
 
       # compare branches only if branches are valid, otherwise
@@ -93,8 +94,12 @@ module MergeRequests
       project_from_params
     end
 
-    def find_target_branch
-      target_branch || target_project.default_branch
+    def set_merge_request_target_branch
+      if source_branch_default? && !target_branch_specified?
+        merge_request.target_branch = nil
+      else
+        merge_request.target_branch ||= target_project.default_branch
+      end
     end
 
     def source_branch_specified?
@@ -149,7 +154,15 @@ module MergeRequests
     end
 
     def same_source_and_target?
-      source_project == target_project && target_branch == source_branch
+      same_source_and_target_project? && target_branch == source_branch
+    end
+
+    def source_branch_default?
+      same_source_and_target_project? && source_branch == target_project.default_branch
+    end
+
+    def same_source_and_target_project?
+      source_project == target_project
     end
 
     def source_branch_exists?
diff --git a/app/views/projects/merge_requests/creations/_new_compare.html.haml b/app/views/projects/merge_requests/creations/_new_compare.html.haml
index be01905dd35..c6615b26bc0 100644
--- a/app/views/projects/merge_requests/creations/_new_compare.html.haml
+++ b/app/views/projects/merge_requests/creations/_new_compare.html.haml
@@ -51,7 +51,7 @@
                   selected: f.object.target_project_id
           .merge-request-select.dropdown
             = f.hidden_field :target_branch
-            = dropdown_toggle f.object.target_branch, { toggle: "dropdown", 'field-name': "#{f.object_name}[target_branch]", 'refs-url': refs_project_path(f.object.target_project), selected: f.object.target_branch }, { toggle_class: "js-compare-dropdown js-target-branch monospace" }
+            = dropdown_toggle f.object.target_branch || _("Select target branch"), { toggle: "dropdown", 'field-name': "#{f.object_name}[target_branch]", 'refs-url': refs_project_path(f.object.target_project), selected: f.object.target_branch }, { toggle_class: "js-compare-dropdown js-target-branch monospace" }
             .dropdown-menu.dropdown-menu-selectable.js-target-branch-dropdown.git-revision-dropdown
               = dropdown_title(_("Select target branch"))
               = dropdown_filter(_("Search branches"))