// Package revlist allows to create the revision history of a file, this
// is, the list of commits in the past that affect the file.
//
// The general idea is to traverse the git commit graph backward,
// flattening the graph into a linear history, and skipping commits that
// are irrelevant for the particular file.
//
// There is no single answer for this operation. The git command
// "git-revlist" returns different histories depending on its arguments
// and some internal heuristics.
//
// The current implementation tries to get something similar to what you
// whould get using git-revlist. See the failing tests for some
// insight about how the current implementation and git-revlist differs.
//
// Another way to get the revision history for a file is:
// git log --follow -p -- file
package revlist
import (
"bytes"
"io"
"sort"
"gopkg.in/src-d/go-git.v2"
"gopkg.in/src-d/go-git.v2/core"
"gopkg.in/src-d/go-git.v2/diff"
"github.com/sergi/go-diff/diffmatchpatch"
)
// A Revs is a list of revisions for a file (basically a list of commits).
// It implements sort.Interface using the commit time.
type Revs []*git.Commit
func (l Revs) Len() int {
return len(l)
}
// sorts from older to newer commit.
func (l Revs) Less(i, j int) bool {
return l[i].Committer.When.Before(l[j].Committer.When)
}
func (l Revs) Swap(i, j int) {
l[i], l[j] = l[j], l[i]
}
// for debugging
func (l Revs) GoString() string {
var buf bytes.Buffer
for _, c := range l {
buf.WriteString(c.Hash.String()[:8])
buf.WriteString("\n")
}
return buf.String()
}
// NewRevs returns a Revs pointer for the
// file at "path", from commit "commit".
// The commits are sorted in commit order.
// It stops searching a branch for a file upon reaching the commit
// were the file was created.
// Moves and copies are not currently supported.
// Cherry-picks are not detected unless there are no commits between
// them and therefore can appear repeated in the list.
// (see git path-id for hints on how to fix this).
func NewRevs(repo *git.Repository, commit *git.Commit, path string) (Revs, error) {
result := make(Revs, 0)
seen := make(map[core.Hash]struct{}, 0)
err := walkGraph(&result, &seen, repo, commit, path)
if err != nil {
return nil, err
}
sort.Sort(result)
result, err = removeComp(path, result, equivalent) // for merges of identical cherry-picks
if err != nil {
return nil, err
}
return result, nil
}
// Recursive traversal of the commit graph, generating a linear history
// of the path.
func walkGraph(result *Revs, seen *map[core.Hash]struct{}, repo *git.Repository, current *git.Commit, path string) error {
// check and update seen
if _, ok := (*seen)[current.Hash]; ok {
return nil
}
(*seen)[current.Hash] = struct{}{}
// if the path is not in the current commit, stop searching.
if _, err := current.File(path); err != nil {
return nil
}
// optimization: don't traverse branches that does not
// contain the path.
parents := parentsContainingPath(path, current)
switch len(parents) {
// if the path is not found in any of its parents, the path was
// created by this commit; we must add it to the revisions list and
// stop searching. This includes the case when current is the
// initial commit.
case 0:
*result = append(*result, current)
return nil
case 1: // only one parent contains the path
// if the file contents has change, add the current commit
different, err := differentContents(path, current, parents)
if err != nil {
return err
}
if len(different) == 1 {
*result = append(*result, current)
}
// in any case, walk the parent
return walkGraph(result, seen, repo, parents[0], path)
default: // more than one parent contains the path
// TODO: detect merges that had a conflict, because they must be
// included in the result here.
for _, p := range parents {
err := walkGraph(result, seen, repo, p, path)
if err != nil {
return err
}
}
}
return nil
}
// TODO: benchmark this making git.Commit.parent public instead of using
// an iterator
func parentsContainingPath(path string, c *git.Commit) []*git.Commit {
var result []*git.Commit
iter := c.Parents()
for {
parent, err := iter.Next()
if err != nil {
if err == io.EOF {
return result
}
panic("unreachable")
}
if _, err := parent.File(path); err == nil {
result = append(result, parent)
}
}
}
// Returns an slice of the commits in "cs" that has the file "path", but with different
// contents than what can be found in "c".
func differentContents(path string, c *git.Commit, cs []*git.Commit) ([]*git.Commit, error) {
result := make([]*git.Commit, 0, len(cs))
h, found := blobHash(path, c)
if !found {
return nil, git.ErrFileNotFound
}
for _, cx := range cs {
if hx, found := blobHash(path, cx); found && h != hx {
result = append(result, cx)
}
}
return result, nil
}
// blobHash returns the hash of a path in a commit
func blobHash(path string, commit *git.Commit) (hash core.Hash, found bool) {
file, err := commit.File(path)
if err != nil {
var empty core.Hash
return empty, found
}
return file.Hash, true
}
type contentsComparatorFn func(path string, a, b *git.Commit) (bool, error)
// Returns a new slice of commits, with duplicates removed. Expects a
// sorted commit list. Duplication is defined according to "comp". It
// will always keep the first commit of a series of duplicated commits.
func removeComp(path string, cs []*git.Commit, comp contentsComparatorFn) ([]*git.Commit, error) {
result := make([]*git.Commit, 0, len(cs))
if len(cs) == 0 {
return result, nil
}
result = append(result, cs[0])
for i := 1; i < len(cs); i++ {
equals, err := comp(path, cs[i], cs[i-1])
if err != nil {
return nil, err
}
if !equals {
result = append(result, cs[i])
}
}
return result, nil
}
// Equivalent commits are commits whose patch is the same.
func equivalent(path string, a, b *git.Commit) (bool, error) {
numParentsA := a.NumParents()
numParentsB := b.NumParents()
// the first commit is not equivalent to anyone
// and "I think" merges can not be equivalent to anything
if numParentsA != 1 || numParentsB != 1 {
return false, nil
}
diffsA, err := patch(a, path)
if err != nil {
return false, err
}
diffsB, err := patch(b, path)
if err != nil {
return false, err
}
return sameDiffs(diffsA, diffsB), nil
}
func patch(c *git.Commit, path string) ([]diffmatchpatch.Diff, error) {
// get contents of the file in the commit
file, err := c.File(path)
if err != nil {
return nil, err
}
content := file.Contents()
// get contents of the file in the first parent of the commit
var contentParent string
iter := c.Parents()
parent, err := iter.Next()
if err != nil {
return nil, err
}
file, err = parent.File(path)
if err != nil {
contentParent = ""
} else {
contentParent = file.Contents()
}
// compare the contents of parent and child
return diff.Do(content, contentParent), nil
}
func sameDiffs(a, b []diffmatchpatch.Diff) bool {
if len(a) != len(b) {
return false
}
for i := range a {
if !sameDiff(a[i], b[i]) {
return false
}
}
return true
}
func sameDiff(a, b diffmatchpatch.Diff) bool {
if a.Type != b.Type {
return false
}
switch a.Type {
case 0:
return git.CountLines(a.Text) == git.CountLines(b.Text)
case 1, -1:
return a.Text == b.Text
default:
panic("unreachable")
}
}
