Add `source_branch` option for various git operations

If `source_branch` option is passed, and target branch cannot be found,
`Repository#update_branch_with_hooks` would try to create a new branch
from `source_branch`.

This way, we could make changes in the new branch while only firing
the hooks once for the changes. Previously, we can only create a new
branch first then make changes to the new branch, firing hooks twice.
This behaviour is bad for CI.

Fixes #7237

1 files changed, 22 insertions, 0 deletions

diff --git a/app/services/validate_new_branch_service.rb b/app/services/validate_new_branch_service.rb
new file mode 100644
index 00000000000..2f61be184ce
--- /dev/null
+++ b/app/services/validate_new_branch_service.rb
@@ -0,0 +1,22 @@
+require_relative 'base_service'
+
+class ValidateNewBranchService < BaseService
+  def execute(branch_name)
+    valid_branch = Gitlab::GitRefValidator.validate(branch_name)
+
+    unless valid_branch
+      return error('Branch name is invalid')
+    end
+
+    repository = project.repository
+    existing_branch = repository.find_branch(branch_name)
+
+    if existing_branch
+      return error('Branch already exists')
+    end
+
+    success
+  rescue GitHooksService::PreReceiveError => ex
+    error(ex.message)
+  end
+end