Add latest commit's SHA to content response (#20398)

* Add latest commit's SHA to content response

- When requesting the contents of a filepath, add the latest commit's
SHA to the requested file.
- Resolves #12840

* Add swagger

* Fix NPE

* Fix tests

* Hook into LastCommitCache

* Move AddLastCommitCache to a common nogogit and gogit file

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Prevent NPE

Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/git/repo_commit.go

@@ -11,6 +11,7 @@ import (
 	"strconv"
 	"strings"
 
+	"code.gitea.io/gitea/modules/cache"
 	"code.gitea.io/gitea/modules/setting"
 )
 
@@ -434,3 +435,20 @@ func (repo *Repository) IsCommitInBranch(commitID, branch string) (r bool, err e
 	}
 	return len(stdout) > 0, err
 }
+
+func (repo *Repository) AddLastCommitCache(cacheKey, fullName, sha string) error {
+	if repo.LastCommitCache == nil {
+		commitsCount, err := cache.GetInt64(cacheKey, func() (int64, error) {
+			commit, err := repo.GetCommit(sha)
+			if err != nil {
+				return 0, err
+			}
+			return commit.CommitsCount()
+		})
+		if err != nil {
+			return err
+		}
+		repo.LastCommitCache = NewLastCommitCache(commitsCount, fullName, repo, cache.GetCache())
+	}
+	return nil
+}