Defer Last Commit Info (#16467)

One of the biggest reasons for slow repository browsing is that we wait
until last commit information has been generated for all files in the
repository.

This PR proposes deferring this generation to a new POST endpoint that
does the look up outside of the main page request.

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

modules/git/log_name_status.go

@@ -275,7 +275,9 @@ func (g *LogNameStatusRepoParser) Close() {
 }
 
 // WalkGitLog walks the git log --name-status for the head commit in the provided treepath and files
-func WalkGitLog(ctx context.Context, repo *Repository, head *Commit, treepath string, paths ...string) (map[string]string, error) {
+func WalkGitLog(ctx context.Context, cache *LastCommitCache, repo *Repository, head *Commit, treepath string, paths ...string) (map[string]string, error) {
+	headRef := head.ID.String()
+
 	tree, err := head.SubTree(treepath)
 	if err != nil {
 		return nil, err
@@ -339,6 +341,9 @@ heaploop:
 	for {
 		select {
 		case <-ctx.Done():
+			if ctx.Err() == context.DeadlineExceeded {
+				break heaploop
+			}
 			g.Close()
 			return nil, ctx.Err()
 		default:
@@ -360,10 +365,16 @@ heaploop:
 				changed[i] = false
 				if results[i] == "" {
 					results[i] = current.CommitID
+					if err := cache.Put(headRef, path.Join(treepath, paths[i]), current.CommitID); err != nil {
+						return nil, err
+					}
 					delete(path2idx, paths[i])
 					remaining--
 					if results[0] == "" {
 						results[0] = current.CommitID
+						if err := cache.Put(headRef, treepath, current.CommitID); err != nil {
+							return nil, err
+						}
 						delete(path2idx, "")
 						remaining--
 					}