// Package blame contains blaming functionality for files in the repo.
//
// Blaming a file is finding what commit was the last to modify each of
// the lines in the file, therefore the output of a blaming operation is
// usually a slice of commits, one commit per line in the file.
//
// This package also provides a pretty print function to output the
// results of a blame in a similar format to the git-blame command.
package git
import (
"bytes"
"errors"
"fmt"
"strconv"
"strings"
"unicode/utf8"
"gopkg.in/src-d/go-git.v2/core"
"gopkg.in/src-d/go-git.v2/diff"
)
type Blame struct {
Path string
Rev core.Hash
Lines []*line
}
// Blame returns the last commit that modified each line of a file in a
// repository.
//
// The file to blame is identified by the input arguments: repo, commit and path.
// The output is a slice of commits, one for each line in the file.
//
// Blaming a file is a two step process:
//
// 1. Create a linear history of the commits affecting a file. We use
// revlist.New for that.
//
// 2. Then build a graph with a node for every line in every file in
// the history of the file.
//
// Each node (line) holds the commit where it was introduced or
// last modified. To achieve that we use the FORWARD algorithm
// described in Zimmermann, et al. "Mining Version Archives for
// Co-changed Lines", in proceedings of the Mining Software
// Repositories workshop, Shanghai, May 22-23, 2006.
//
// Each node is asigned a commit: Start by the nodes in the first
// commit. Assign that commit as the creator of all its lines.
//
// Then jump to the nodes in the next commit, and calculate the diff
// between the two files. Newly created lines get
// assigned the new commit as its origin. Modified lines also get
// this new commit. Untouched lines retain the old commit.
//
// All this work is done in the assignOrigin function which holds all
// the internal relevant data in a "blame" struct, that is not
// exported.
//
// TODO: ways to improve the efficiency of this function:
//
// 1. Improve revlist
//
// 2. Improve how to traverse the history (example a backward
// traversal will be much more efficient)
//
// TODO: ways to improve the function in general:
//
// 1. Add memoization between revlist and assign.
//
// 2. It is using much more memory than needed, see the TODOs below.
func (c *Commit) Blame(path string) (*Blame, error) {
b := new(blame)
b.fRev = c
b.path = path
// get all the file revisions
if err := b.fillRevs(); err != nil {
return nil, err
}
// calculate the line tracking graph and fill in
// file contents in data.
if err := b.fillGraphAndData(); err != nil {
return nil, err
}
file, err := b.fRev.File(b.path)
if err != nil {
return nil, err
}
finalLines := file.Lines()
lines, err := newLines(finalLines, b.sliceGraph(len(b.graph)-1))
if err != nil {
return nil, err
}
return &Blame{
Path: path,
Rev: c.Hash,
Lines: lines,
}, nil
}
type line struct {
author string
text string
}
func newLine(author, text string) *line {
return &line{
author: author,
text: text,
}
}
func newLines(contents []string, commits []*Commit) ([]*line, error) {
if len(contents) != len(commits) {
return nil, errors.New("contents and commits have different length")
}
result := make([]*line, 0, len(contents))
for i := range contents {
l := newLine(commits[i].Author.Email, contents[i])
result = append(result, l)
}
return result, nil
}
// this struct is internally used by the blame function to hold its
// inputs, outputs and state.
type blame struct {
path string // the path of the file to blame
fRev *Commit // the commit of the final revision of the file to blame
revs []*Commit // the chain of revisions affecting the the file to blame
data []string // the contents of the file across all its revisions
graph [][]*Commit // the graph of the lines in the file across all the revisions TODO: not all commits are needed, only the current rev and the prev
}
// calculte the history of a file "path", starting from commit "from", sorted by commit date.
func (b *blame) fillRevs() error {
var err error
b.revs, err = b.fRev.References(b.path)
if err != nil {
return err
}
return nil
}
// build graph of a file from its revision history
func (b *blame) fillGraphAndData() error {
b.graph = make([][]*Commit, len(b.revs))
b.data = make([]string, len(b.revs)) // file contents in all the revisions
// for every revision of the file, starting with the first
// one...
for i, rev := range b.revs {
// get the contents of the file
file, err := rev.File(b.path)
if err != nil {
return nil
}
b.data[i] = file.Contents()
nLines := countLines(b.data[i])
// create a node for each line
b.graph[i] = make([]*Commit, nLines)
// assign a commit to each node
// if this is the first revision, then the node is assigned to
// this first commit.
if i == 0 {
for j := 0; j < nLines; j++ {
b.graph[i][j] = (*Commit)(b.revs[i])
}
} else {
// if this is not the first commit, then assign to the old
// commit or to the new one, depending on what the diff
// says.
b.assignOrigin(i, i-1)
}
}
return nil
}
// sliceGraph returns a slice of commits (one per line) for a particular
// revision of a file (0=first revision).
func (b *blame) sliceGraph(i int) []*Commit {
fVs := b.graph[i]
result := make([]*Commit, 0, len(fVs))
for _, v := range fVs {
c := Commit(*v)
result = append(result, &c)
}
return result
}
// Assigns origin to vertexes in current (c) rev from data in its previous (p)
// revision
func (b *blame) assignOrigin(c, p int) {
// assign origin based on diff info
hunks := diff.Do(b.data[p], b.data[c])
sl := -1 // source line
dl := -1 // destination line
for h := range hunks {
hLines := countLines(hunks[h].Text)
for hl := 0; hl < hLines; hl++ {
switch {
case hunks[h].Type == 0:
sl++
dl++
b.graph[c][dl] = b.graph[p][sl]
case hunks[h].Type == 1:
dl++
b.graph[c][dl] = (*Commit)(b.revs[c])
case hunks[h].Type == -1:
sl++
default:
panic("unreachable")
}
}
}
}
// GoString prints the results of a Blame using git-blame's style.
func (b *blame) GoString() string {
var buf bytes.Buffer
file, err := b.fRev.File(b.path)
if err != nil {
panic("PrettyPrint: internal error in repo.Data")
}
contents := file.Contents()
lines := strings.Split(contents, "\n")
// max line number length
mlnl := len(fmt.Sprintf("%s", strconv.Itoa(len(lines))))
// max author length
mal := b.maxAuthorLength()
format := fmt.Sprintf("%%s (%%-%ds %%%dd) %%s\n",
mal, mlnl)
fVs := b.graph[len(b.graph)-1]
for ln, v := range fVs {
fmt.Fprintf(&buf, format, v.Hash.String()[:8],
prettyPrintAuthor(fVs[ln]), ln+1, lines[ln])
}
return buf.String()
}
// utility function to pretty print the author.
func prettyPrintAuthor(c *Commit) string {
return fmt.Sprintf("%s %s", c.Author.Name, c.Author.When.Format("2006-01-02"))
}
// utility function to calculate the number of runes needed
// to print the longest author name in the blame of a file.
func (b *blame) maxAuthorLength() int {
memo := make(map[core.Hash]struct{}, len(b.graph)-1)
fVs := b.graph[len(b.graph)-1]
m := 0
for ln := range fVs {
if _, ok := memo[fVs[ln].Hash]; ok {
continue
}
memo[fVs[ln].Hash] = struct{}{}
m = max(m, utf8.RuneCountInString(prettyPrintAuthor(fVs[ln])))
}
return m
}
func max(a, b int) int {
if a > b {
return a
}
return b
}
