Add start_sha to commits API

When passing start_branch on committing from the WebIDE, it's possible
that the branch has changed since editing started, which results in the
change being applied on top of the latest commit in the branch and
overwriting the new changes.

By passing the start_sha instead we can make sure that the change is
applied on top of the commit which the user started editing from.

1 files changed, 9 insertions, 5 deletions

diff --git a/lib/api/commits.rb b/lib/api/commits.rb
index c414ad75d9d..0aeb9584641 100644
--- a/lib/api/commits.rb
+++ b/lib/api/commits.rb
@@ -76,7 +76,7 @@ module API
         detail 'This feature was introduced in GitLab 8.13'
       end
       params do
-        requires :branch, type: String, desc: 'Name of the branch to commit into. To create a new branch, also provide `start_branch`.', allow_blank: false
+        requires :branch, type: String, desc: 'Name of the branch to commit into. To create a new branch, also provide either `start_branch` or `start_sha`, and optionally `start_project`.', allow_blank: false
         requires :commit_message, type: String, desc: 'Commit message'
         requires :actions, type: Array, desc: 'Actions to perform in commit' do
           requires :action, type: String, desc: 'The action to perform, `create`, `delete`, `move`, `update`, `chmod`', values: %w[create update move delete chmod].freeze
@@ -98,12 +98,16 @@ module API
             requires :execute_filemode, type: Boolean, desc: 'When `true/false` enables/disables the execute flag on the file.'
           end
         end
-        optional :start_branch, type: String, desc: 'Name of the branch to start the new commit from'
-        optional :start_project, types: [Integer, String], desc: 'The ID or path of the project to start the commit from'
+
+        optional :start_branch, type: String, desc: 'Name of the branch to start the new branch from'
+        optional :start_sha, type: String, desc: 'SHA of the commit to start the new branch from'
+        mutually_exclusive :start_branch, :start_sha
+
+        optional :start_project, types: [Integer, String], desc: 'The ID or path of the project to start the new branch from'
         optional :author_email, type: String, desc: 'Author email for commit'
         optional :author_name, type: String, desc: 'Author name for commit'
         optional :stats, type: Boolean, default: true, desc: 'Include commit stats'
-        optional :force, type: Boolean, default: false, desc: 'When `true` overwrites the target branch with a new commit based on the `start_branch`'
+        optional :force, type: Boolean, default: false, desc: 'When `true` overwrites the target branch with a new commit based on the `start_branch` or `start_sha`'
       end
       post ':id/repository/commits' do
         if params[:start_project]
@@ -118,7 +122,7 @@ module API
 
         attrs = declared_params
         attrs[:branch_name] = attrs.delete(:branch)
-        attrs[:start_branch] ||= attrs[:branch_name]
+        attrs[:start_branch] ||= attrs[:branch_name] unless attrs[:start_sha]
         attrs[:start_project] = start_project if start_project
 
         result = ::Files::MultiService.new(user_project, current_user, attrs).execute