Abstract hash function usage (#28138)

Refactor Hash interfaces and centralize hash function. This will allow
easier introduction of different hash function later on.

This forms the "no-op" part of the SHA256 enablement patch.

modules/git/log_name_status.go

@@ -143,17 +143,20 @@ func (g *LogNameStatusRepoParser) Next(treepath string, paths2ids map[string]int
 	}
 
 	// Our "line" must look like: <commitid> SP (<parent> SP) * NUL
-	ret.CommitID = string(g.next[0:40])
-	parents := string(g.next[41:])
+	commitIds := string(g.next)
 	if g.buffull {
 		more, err := g.rd.ReadString('\x00')
 		if err != nil {
 			return nil, err
 		}
-		parents += more
+		commitIds += more
+	}
+	commitIds = commitIds[:len(commitIds)-1]
+	splitIds := strings.Split(commitIds, " ")
+	ret.CommitID = splitIds[0]
+	if len(splitIds) > 1 {
+		ret.ParentIDs = splitIds[1:]
 	}
-	parents = parents[:len(parents)-1]
-	ret.ParentIDs = strings.Split(parents, " ")
 
 	// now read the next "line"
 	g.buffull = false