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, 5 insertions, 0 deletions

diff --git a/lib/gitlab/git.rb b/lib/gitlab/git.rb
index 44a62586a23..df9f33baec2 100644
--- a/lib/gitlab/git.rb
+++ b/lib/gitlab/git.rb
@@ -9,6 +9,7 @@ module Gitlab
     # https://github.com/git/git/blob/3ad8b5bf26362ac67c9020bf8c30eee54a84f56d/cache.h#L1011-L1012
     EMPTY_TREE_ID = '4b825dc642cb6eb9a060e54bf8d69288fbee4904'.freeze
     BLANK_SHA = ('0' * 40).freeze
+    COMMIT_ID = /\A[0-9a-f]{40}\z/.freeze
     TAG_REF_PREFIX = "refs/tags/".freeze
     BRANCH_REF_PREFIX = "refs/heads/".freeze
 
@@ -65,6 +66,10 @@ module Gitlab
         ref == BLANK_SHA
       end
 
+      def commit_id?(ref)
+        COMMIT_ID.match?(ref)
+      end
+
       def version
         Gitlab::Git::Version.git_version
       end