Use commit graph files for listing pages (#7314)

* Experimental support for git commit graph files and bloom filter index

Signed-off-by: Filip Navara <filip.navara@gmail.com>

* Force vendor of commitgraph

Signed-off-by: Filip Navara <filip.navara@gmail.com>

* Remove bloom filter experiment and debug prints

* Remove old code for building commit graphs

* Remove unused function

* Remove mmap usage

* gofmt

* sort vendor/modules.txt

* Add copyright header and log commit-graph error

modules/git/repo_commitgraph.go

@@ -0,0 +1,35 @@
+// Copyright 2019 The Gitea Authors.
+// All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package git
+
+import (
+	"os"
+	"path"
+
+	gitealog "code.gitea.io/gitea/modules/log"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph"
+	cgobject "gopkg.in/src-d/go-git.v4/plumbing/object/commitgraph"
+)
+
+// CommitNodeIndex returns the index for walking commit graph
+func (r *Repository) CommitNodeIndex() (cgobject.CommitNodeIndex, *os.File) {
+	indexPath := path.Join(r.Path, "objects", "info", "commit-graph")
+
+	file, err := os.Open(indexPath)
+	if err == nil {
+		var index commitgraph.Index
+		index, err = commitgraph.OpenFileIndex(file)
+		if err == nil {
+			return cgobject.NewGraphCommitNodeIndex(index, r.gogitRepo.Storer), file
+		}
+	}
+
+	if !os.IsNotExist(err) {
+		gitealog.Warn("Unable to read commit-graph for %s: %v", r.Path, err)
+	}
+
+	return cgobject.NewObjectCommitNodeIndex(r.gogitRepo.Storer), nil
+}