API: Use find_branch! in all places

changelogs/unreleased/api-promote-find-branch.yml

+---
+title: 'API: Use find_branch! in all places'
+merge_request: 21614
+author: Robert Schilling
+type: fixed

lib/api/branches.rb

@@ -9,14 +9,6 @@ module API
     before { authorize! :download_code, user_project }
 
     helpers do
-      def find_branch!(branch_name)
-        begin
-          user_project.repository.find_branch(branch_name) || not_found!('Branch')
-        rescue Gitlab::Git::CommandError
-          render_api_error!('The branch refname is invalid', 400)
-        end
-      end
-
       params :filter_params do
         optional :search, type: String, desc: 'Return list of branches matching the search criteria'
         optional :sort, type: String, desc: 'Return list of branches sorted by the given field'

lib/api/commits.rb

@@ -159,8 +159,7 @@ module API
         commit = user_project.commit(params[:sha])
         not_found!('Commit') unless commit
 
-        branch = user_project.repository.find_branch(params[:branch])
-        not_found!('Branch') unless branch
+        find_branch!(params[:branch])
 
         commit_params = {
           commit: commit,
@@ -171,7 +170,7 @@ module API
         result = ::Commits::CherryPickService.new(user_project, current_user, commit_params).execute
 
         if result[:status] == :success
-          branch = user_project.repository.find_branch(params[:branch])
+          branch = find_branch!(params[:branch])
           present user_project.repository.commit(branch.dereferenced_target), with: Entities::Commit
         else
           render_api_error!(result[:message], 400)

lib/api/helpers.rb

@@ -156,6 +156,14 @@ module API
       end
     end
 
+    def find_branch!(branch_name)
+      begin
+        user_project.repository.find_branch(branch_name) || not_found!('Branch')
+      rescue Gitlab::Git::CommandError
+        render_api_error!('The branch refname is invalid', 400)
+      end
+    end
+
     def find_project_label(id)
       labels = available_labels_for(user_project)
       label = labels.find_by_id(id) || labels.find_by_title(id)