plumbing: object, adds tree path cache to trees. Fixes #793

The cache is used in Tree.FindEntry for faster path search.

Signed-off-by: Javi Fontan <jfontan@gmail.com>

Author: jfontan

plumbing/object/tree.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"path"
+	"path/filepath"
 	"strings"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
@@ -34,6 +35,7 @@ type Tree struct {
 
 	s storer.EncodedObjectStorer
 	m map[string]*TreeEntry
+	t map[string]*Tree // tree path cache
 }
 
 // GetTree gets a tree from an object storer and decodes it.
@@ -111,14 +113,37 @@ func (t *Tree) TreeEntryFile(e *TreeEntry) (*File, error) {
 
 // FindEntry search a TreeEntry in this tree or any subtree.
 func (t *Tree) FindEntry(path string) (*TreeEntry, error) {
+	if t.t == nil {
+		t.t = make(map[string]*Tree)
+	}
+
 	pathParts := strings.Split(path, "/")
+	startingTree := t
+	pathCurrent := ""
+
+	// search for the longest path in the tree path cache
+	for i := len(pathParts); i > 1; i-- {
+		path := filepath.Join(pathParts[:i]...)
+
+		tree, ok := t.t[path]
+		if ok {
+			startingTree = tree
+			pathParts = pathParts[i:]
+			pathCurrent = path
+
+			break
+		}
+	}
 
 	var tree *Tree
 	var err error
-	for tree = t; len(pathParts) > 1; pathParts = pathParts[1:] {
+	for tree = startingTree; len(pathParts) > 1; pathParts = pathParts[1:] {
 		if tree, err = tree.dir(pathParts[0]); err != nil {
 			return nil, err
 		}
+
+		pathCurrent = filepath.Join(pathCurrent, pathParts[0])
+		t.t[pathCurrent] = tree
 	}
 
 	return tree.entry(pathParts[0])