Add example for commit-graph traversal

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

Author: filipnavara

_examples/ls/main.go

@@ -0,0 +1,268 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path"
+	"strings"
+
+	"github.com/emirpasic/gods/trees/binaryheap"
+	"gopkg.in/src-d/go-git.v4"
+	. "gopkg.in/src-d/go-git.v4/_examples"
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/cache"
+	commitgraph_fmt "gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph"
+	"gopkg.in/src-d/go-git.v4/plumbing/object"
+	"gopkg.in/src-d/go-git.v4/plumbing/object/commitgraph"
+	"gopkg.in/src-d/go-git.v4/storage/filesystem"
+
+	"gopkg.in/src-d/go-billy.v4"
+	"gopkg.in/src-d/go-billy.v4/osfs"
+)
+
+// Example how to resolve a revision into its commit counterpart
+func main() {
+	CheckArgs("<path>", "<revision>", "<tree path>")
+
+	path := os.Args[1]
+	revision := os.Args[2]
+	treePath := os.Args[3]
+
+	// We instantiate a new repository targeting the given path (the .git folder)
+	fs := osfs.New(path)
+	s := filesystem.NewStorageWithOptions(fs, cache.NewObjectLRUDefault(), filesystem.Options{KeepDescriptors: true})
+	r, err := git.Open(s, fs)
+	CheckIfError(err)
+
+	// Resolve revision into a sha1 commit, only some revisions are resolved
+	// look at the doc to get more details
+	Info("git rev-parse %s", revision)
+
+	h, err := r.ResolveRevision(plumbing.Revision(revision))
+	CheckIfError(err)
+
+	commit, err := r.CommitObject(*h)
+	CheckIfError(err)
+
+	tree, err := commit.Tree()
+	CheckIfError(err)
+	if treePath != "" {
+		tree, err = tree.Tree(treePath)
+		CheckIfError(err)
+	}
+
+	var paths []string
+	for _, entry := range tree.Entries {
+		paths = append(paths, entry.Name)
+	}
+
+	commitNodeIndex, file := getCommitNodeIndex(r, fs)
+	if file != nil {
+		defer file.Close()
+	}
+
+	commitNode, err := commitNodeIndex.Get(*h)
+	CheckIfError(err)
+
+	revs, err := getLastCommitForPaths(commitNode, treePath, paths)
+	CheckIfError(err)
+	for path, rev := range revs {
+		// Print one line per file (name hash message)
+		hash := rev.Hash.String()
+		line := strings.Split(rev.Message, "\n")
+		fmt.Println(path, hash[:7], line[0])
+	}
+
+	s.Close()
+}
+
+func getCommitNodeIndex(r *git.Repository, fs billy.Filesystem) (commitgraph.CommitNodeIndex, io.ReadCloser) {
+	file, err := fs.Open(path.Join("objects", "info", "commit-graph"))
+	if err == nil {
+		index, err := commitgraph_fmt.OpenFileIndex(file)
+		if err == nil {
+			return commitgraph.NewGraphCommitNodeIndex(index, r.Storer), file
+		}
+		file.Close()
+	}
+
+	return commitgraph.NewObjectCommitNodeIndex(r.Storer), nil
+}
+
+type commitAndPaths struct {
+	commit commitgraph.CommitNode
+	// Paths that are still on the branch represented by commit
+	paths []string
+	// Set of hashes for the paths
+	hashes map[string]plumbing.Hash
+}
+
+func getCommitTree(c commitgraph.CommitNode, treePath string) (*object.Tree, error) {
+	tree, err := c.Tree()
+	if err != nil {
+		return nil, err
+	}
+
+	// Optimize deep traversals by focusing only on the specific tree
+	if treePath != "" {
+		tree, err = tree.Tree(treePath)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return tree, nil
+}
+
+func getFullPath(treePath, path string) string {
+	if treePath != "" {
+		if path != "" {
+			return treePath + "/" + path
+		}
+		return treePath
+	}
+	return path
+}
+
+func getFileHashes(c commitgraph.CommitNode, treePath string, paths []string) (map[string]plumbing.Hash, error) {
+	tree, err := getCommitTree(c, treePath)
+	if err == object.ErrDirectoryNotFound {
+		// The whole tree didn't exist, so return empty map
+		return make(map[string]plumbing.Hash), nil
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	hashes := make(map[string]plumbing.Hash)
+	for _, path := range paths {
+		if path != "" {
+			entry, err := tree.FindEntry(path)
+			if err == nil {
+				hashes[path] = entry.Hash
+			}
+		} else {
+			hashes[path] = tree.Hash
+		}
+	}
+
+	return hashes, nil
+}
+
+func getLastCommitForPaths(c commitgraph.CommitNode, treePath string, paths []string) (map[string]*object.Commit, error) {
+	// We do a tree traversal with nodes sorted by commit time
+	heap := binaryheap.NewWith(func(a, b interface{}) int {
+		if a.(*commitAndPaths).commit.CommitTime().Before(b.(*commitAndPaths).commit.CommitTime()) {
+			return 1
+		}
+		return -1
+	})
+
+	resultNodes := make(map[string]commitgraph.CommitNode)
+	initialHashes, err := getFileHashes(c, treePath, paths)
+	if err != nil {
+		return nil, err
+	}
+
+	// Start search from the root commit and with full set of paths
+	heap.Push(&commitAndPaths{c, paths, initialHashes})
+
+	for {
+		cIn, ok := heap.Pop()
+		if !ok {
+			break
+		}
+		current := cIn.(*commitAndPaths)
+
+		// Load the parent commits for the one we are currently examining
+		numParents := current.commit.NumParents()
+		var parents []commitgraph.CommitNode
+		for i := 0; i < numParents; i++ {
+			parent, err := current.commit.ParentNode(i)
+			if err != nil {
+				break
+			}
+			parents = append(parents, parent)
+		}
+
+		// Examine the current commit and set of interesting paths
+		pathUnchanged := make([]bool, len(current.paths))
+		parentHashes := make([]map[string]plumbing.Hash, len(parents))
+		for j, parent := range parents {
+			parentHashes[j], err = getFileHashes(parent, treePath, current.paths)
+			if err != nil {
+				break
+			}
+
+			for i, path := range current.paths {
+				if parentHashes[j][path] == current.hashes[path] {
+					pathUnchanged[i] = true
+				}
+			}
+		}
+
+		var remainingPaths []string
+		for i, path := range current.paths {
+			// The results could already contain some newer change for the same path,
+			// so don't override that and bail out on the file early.
+			if resultNodes[path] == nil {
+				if pathUnchanged[i] {
+					// The path existed with the same hash in at least one parent so it could
+					// not have been changed in this commit directly.
+					remainingPaths = append(remainingPaths, path)
+				} else {
+					// There are few possible cases how can we get here:
+					// - The path didn't exist in any parent, so it must have been created by
+					//   this commit.
+					// - The path did exist in the parent commit, but the hash of the file has
+					//   changed.
+					// - We are looking at a merge commit and the hash of the file doesn't
+					//   match any of the hashes being merged. This is more common for directories,
+					//   but it can also happen if a file is changed through conflict resolution.
+					resultNodes[path] = current.commit
+				}
+			}
+		}
+
+		if len(remainingPaths) > 0 {
+			// Add the parent nodes along with remaining paths to the heap for further
+			// processing.
+			for j, parent := range parents {
+				// Combine remainingPath with paths available on the parent branch
+				// and make union of them
+				remainingPathsForParent := make([]string, 0, len(remainingPaths))
+				newRemainingPaths := make([]string, 0, len(remainingPaths))
+				for _, path := range remainingPaths {
+					if parentHashes[j][path] == current.hashes[path] {
+						remainingPathsForParent = append(remainingPathsForParent, path)
+					} else {
+						newRemainingPaths = append(newRemainingPaths, path)
+					}
+				}
+
+				if remainingPathsForParent != nil {
+					heap.Push(&commitAndPaths{parent, remainingPathsForParent, parentHashes[j]})
+				}
+
+				if len(newRemainingPaths) == 0 {
+					break
+				} else {
+					remainingPaths = newRemainingPaths
+				}
+			}
+		}
+	}
+
+	// Post-processing
+	result := make(map[string]*object.Commit)
+	for path, commitNode := range resultNodes {
+		var err error
+		result[path], err = commitNode.Commit()
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return result, nil
+}