forgejo/services/gitdiff/gitdiff.go

// Copyright 2014 The Gogs Authors. All rights reserved.
// 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 gitdiff

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"html/template"
	"io"
	"io/ioutil"
	"net/url"
	"os"
	"os/exec"
	"regexp"
	"sort"
	"strings"

	"code.gitea.io/gitea/models"
	"code.gitea.io/gitea/modules/charset"
	"code.gitea.io/gitea/modules/git"
	"code.gitea.io/gitea/modules/highlight"
	"code.gitea.io/gitea/modules/log"
	"code.gitea.io/gitea/modules/process"
	"code.gitea.io/gitea/modules/setting"

	"github.com/sergi/go-diff/diffmatchpatch"
	stdcharset "golang.org/x/net/html/charset"
	"golang.org/x/text/transform"
)

// DiffLineType represents the type of a DiffLine.
type DiffLineType uint8

// DiffLineType possible values.
const (
	DiffLinePlain DiffLineType = iota + 1
	DiffLineAdd
	DiffLineDel
	DiffLineSection
)

// DiffFileType represents the type of a DiffFile.
type DiffFileType uint8

// DiffFileType possible values.
const (
	DiffFileAdd DiffFileType = iota + 1
	DiffFileChange
	DiffFileDel
	DiffFileRename
	DiffFileCopy
)

// DiffLineExpandDirection represents the DiffLineSection expand direction
type DiffLineExpandDirection uint8

// DiffLineExpandDirection possible values.
const (
	DiffLineExpandNone DiffLineExpandDirection = iota + 1
	DiffLineExpandSingle
	DiffLineExpandUpDown
	DiffLineExpandUp
	DiffLineExpandDown
)

// DiffLine represents a line difference in a DiffSection.
type DiffLine struct {
	LeftIdx     int
	RightIdx    int
	Type        DiffLineType
	Content     string
	Comments    []*models.Comment
	SectionInfo *DiffLineSectionInfo
}

// DiffLineSectionInfo represents diff line section meta data
type DiffLineSectionInfo struct {
	Path          string
	LastLeftIdx   int
	LastRightIdx  int
	LeftIdx       int
	RightIdx      int
	LeftHunkSize  int
	RightHunkSize int
}

// BlobExcerptChunkSize represent max lines of excerpt
const BlobExcerptChunkSize = 20

// GetType returns the type of a DiffLine.
func (d *DiffLine) GetType() int {
	return int(d.Type)
}

// CanComment returns whether or not a line can get commented
func (d *DiffLine) CanComment() bool {
	return len(d.Comments) == 0 && d.Type != DiffLineSection
}

// GetCommentSide returns the comment side of the first comment, if not set returns empty string
func (d *DiffLine) GetCommentSide() string {
	if len(d.Comments) == 0 {
		return ""
	}
	return d.Comments[0].DiffSide()
}

// GetLineTypeMarker returns the line type marker
func (d *DiffLine) GetLineTypeMarker() string {
	if strings.IndexByte(" +-", d.Content[0]) > -1 {
		return d.Content[0:1]
	}
	return ""
}

// GetBlobExcerptQuery builds query string to get blob excerpt
func (d *DiffLine) GetBlobExcerptQuery() string {
	query := fmt.Sprintf(
		"last_left=%d&last_right=%d&"+
			"left=%d&right=%d&"+
			"left_hunk_size=%d&right_hunk_size=%d&"+
			"path=%s",
		d.SectionInfo.LastLeftIdx, d.SectionInfo.LastRightIdx,
		d.SectionInfo.LeftIdx, d.SectionInfo.RightIdx,
		d.SectionInfo.LeftHunkSize, d.SectionInfo.RightHunkSize,
		url.QueryEscape(d.SectionInfo.Path))
	return query
}

// GetExpandDirection gets DiffLineExpandDirection
func (d *DiffLine) GetExpandDirection() DiffLineExpandDirection {
	if d.Type != DiffLineSection || d.SectionInfo == nil || d.SectionInfo.RightIdx-d.SectionInfo.LastRightIdx <= 1 {
		return DiffLineExpandNone
	}
	if d.SectionInfo.LastLeftIdx <= 0 && d.SectionInfo.LastRightIdx <= 0 {
		return DiffLineExpandUp
	} else if d.SectionInfo.RightIdx-d.SectionInfo.LastRightIdx > BlobExcerptChunkSize && d.SectionInfo.RightHunkSize > 0 {
		return DiffLineExpandUpDown
	} else if d.SectionInfo.LeftHunkSize <= 0 && d.SectionInfo.RightHunkSize <= 0 {
		return DiffLineExpandDown
	}
	return DiffLineExpandSingle
}

func getDiffLineSectionInfo(treePath, line string, lastLeftIdx, lastRightIdx int) *DiffLineSectionInfo {
	leftLine, leftHunk, rightLine, righHunk := git.ParseDiffHunkString(line)

	return &DiffLineSectionInfo{
		Path:          treePath,
		LastLeftIdx:   lastLeftIdx,
		LastRightIdx:  lastRightIdx,
		LeftIdx:       leftLine,
		RightIdx:      rightLine,
		LeftHunkSize:  leftHunk,
		RightHunkSize: righHunk,
	}
}

// escape a line's content or return <br> needed for copy/paste purposes
func getLineContent(content string) string {
	if len(content) > 0 {
		return content
	}
	return "\n"
}

// DiffSection represents a section of a DiffFile.
type DiffSection struct {
	FileName string
	Name     string
	Lines    []*DiffLine
}

var (
	addedCodePrefix   = []byte(`<span class="added-code">`)
	removedCodePrefix = []byte(`<span class="removed-code">`)
	codeTagSuffix     = []byte(`</span>`)
)
var addSpanRegex = regexp.MustCompile(`<span [class="[a-z]*]*$`)

func diffToHTML(fileName string, diffs []diffmatchpatch.Diff, lineType DiffLineType) template.HTML {
	buf := bytes.NewBuffer(nil)
	var addSpan string
	for i := range diffs {
		switch {
		case diffs[i].Type == diffmatchpatch.DiffEqual:
			// Looking for the case where our 3rd party diff library previously detected a string difference
			// in the middle of a span class because we highlight them first. This happens when added/deleted code
			// also changes the chroma class name, either partially or fully. If found, just move the openining span code forward into the next section
			// see TestDiffToHTML for examples
			if len(addSpan) > 0 {
				diffs[i].Text = addSpan + diffs[i].Text
				addSpan = ""
			}
			m := addSpanRegex.FindStringSubmatchIndex(diffs[i].Text)
			if m != nil {
				addSpan = diffs[i].Text[m[0]:m[1]]
				buf.WriteString(strings.TrimSuffix(diffs[i].Text, addSpan))
			} else {
				addSpan = ""
				buf.WriteString(getLineContent(diffs[i].Text))
			}
		case diffs[i].Type == diffmatchpatch.DiffInsert && lineType == DiffLineAdd:
			if len(addSpan) > 0 {
				diffs[i].Text = addSpan + diffs[i].Text
				addSpan = ""
			}
			// Print existing closing span first before opening added-code span so it doesn't unintentionally close it
			if strings.HasPrefix(diffs[i].Text, "</span>") {
				buf.WriteString("</span>")
				diffs[i].Text = strings.TrimPrefix(diffs[i].Text, "</span>")
			}
			m := addSpanRegex.FindStringSubmatchIndex(diffs[i].Text)
			if m != nil {
				addSpan = diffs[i].Text[m[0]:m[1]]
				diffs[i].Text = strings.TrimSuffix(diffs[i].Text, addSpan)
			}
			buf.Write(addedCodePrefix)
			buf.WriteString(getLineContent(diffs[i].Text))
			buf.Write(codeTagSuffix)
		case diffs[i].Type == diffmatchpatch.DiffDelete && lineType == DiffLineDel:
			if len(addSpan) > 0 {
				diffs[i].Text = addSpan + diffs[i].Text
				addSpan = ""
			}
			if strings.HasPrefix(diffs[i].Text, "</span>") {
				buf.WriteString("</span>")
				diffs[i].Text = strings.TrimPrefix(diffs[i].Text, "</span>")
			}
			m := addSpanRegex.FindStringSubmatchIndex(diffs[i].Text)
			if m != nil {
				addSpan = diffs[i].Text[m[0]:m[1]]
				diffs[i].Text = strings.TrimSuffix(diffs[i].Text, addSpan)
			}
			buf.Write(removedCodePrefix)
			buf.WriteString(getLineContent(diffs[i].Text))
			buf.Write(codeTagSuffix)
		}
	}
	return template.HTML(buf.Bytes())
}

// GetLine gets a specific line by type (add or del) and file line number
func (diffSection *DiffSection) GetLine(lineType DiffLineType, idx int) *DiffLine {
	var (
		difference    = 0
		addCount      = 0
		delCount      = 0
		matchDiffLine *DiffLine
	)

LOOP:
	for _, diffLine := range diffSection.Lines {
		switch diffLine.Type {
		case DiffLineAdd:
			addCount++
		case DiffLineDel:
			delCount++
		default:
			if matchDiffLine != nil {
				break LOOP
			}
			difference = diffLine.RightIdx - diffLine.LeftIdx
			addCount = 0
			delCount = 0
		}

		switch lineType {
		case DiffLineDel:
			if diffLine.RightIdx == 0 && diffLine.LeftIdx == idx-difference {
				matchDiffLine = diffLine
			}
		case DiffLineAdd:
			if diffLine.LeftIdx == 0 && diffLine.RightIdx == idx+difference {
				matchDiffLine = diffLine
			}
		}
	}

	if addCount == delCount {
		return matchDiffLine
	}
	return nil
}

var diffMatchPatch = diffmatchpatch.New()

func init() {
	diffMatchPatch.DiffEditCost = 100
}

// GetComputedInlineDiffFor computes inline diff for the given line.
func (diffSection *DiffSection) GetComputedInlineDiffFor(diffLine *DiffLine) template.HTML {
	if setting.Git.DisableDiffHighlight {
		return template.HTML(getLineContent(diffLine.Content[1:]))
	}

	var (
		compareDiffLine *DiffLine
		diff1           string
		diff2           string
	)

	// try to find equivalent diff line. ignore, otherwise
	switch diffLine.Type {
	case DiffLineSection:
		return template.HTML(getLineContent(diffLine.Content[1:]))
	case DiffLineAdd:
		compareDiffLine = diffSection.GetLine(DiffLineDel, diffLine.RightIdx)
		if compareDiffLine == nil {
			return template.HTML(highlight.Code(diffSection.FileName, diffLine.Content[1:]))
		}
		diff1 = compareDiffLine.Content
		diff2 = diffLine.Content
	case DiffLineDel:
		compareDiffLine = diffSection.GetLine(DiffLineAdd, diffLine.LeftIdx)
		if compareDiffLine == nil {
			return template.HTML(highlight.Code(diffSection.FileName, diffLine.Content[1:]))
		}
		diff1 = diffLine.Content
		diff2 = compareDiffLine.Content
	default:
		if strings.IndexByte(" +-", diffLine.Content[0]) > -1 {
			return template.HTML(highlight.Code(diffSection.FileName, diffLine.Content[1:]))
		}
		return template.HTML(highlight.Code(diffSection.FileName, diffLine.Content))
	}

	diffRecord := diffMatchPatch.DiffMain(highlight.Code(diffSection.FileName, diff1[1:]), highlight.Code(diffSection.FileName, diff2[1:]), true)
	diffRecord = diffMatchPatch.DiffCleanupEfficiency(diffRecord)
	return diffToHTML(diffSection.FileName, diffRecord, diffLine.Type)
}

// DiffFile represents a file diff.
type DiffFile struct {
	Name               string
	OldName            string
	Index              int
	Addition, Deletion int
	Type               DiffFileType
	IsCreated          bool
	IsDeleted          bool
	IsBin              bool
	IsLFSFile          bool
	IsRenamed          bool
	IsSubmodule        bool
	Sections           []*DiffSection
	IsIncomplete       bool
}

// GetType returns type of diff file.
func (diffFile *DiffFile) GetType() int {
	return int(diffFile.Type)
}

// GetTailSection creates a fake DiffLineSection if the last section is not the end of the file
func (diffFile *DiffFile) GetTailSection(gitRepo *git.Repository, leftCommitID, rightCommitID string) *DiffSection {
	if len(diffFile.Sections) == 0 || diffFile.Type != DiffFileChange || diffFile.IsBin || diffFile.IsLFSFile {
		return nil
	}
	leftCommit, err := gitRepo.GetCommit(leftCommitID)
	if err != nil {
		return nil
	}
	rightCommit, err := gitRepo.GetCommit(rightCommitID)
	if err != nil {
		return nil
	}
	lastSection := diffFile.Sections[len(diffFile.Sections)-1]
	lastLine := lastSection.Lines[len(lastSection.Lines)-1]
	leftLineCount := getCommitFileLineCount(leftCommit, diffFile.Name)
	rightLineCount := getCommitFileLineCount(rightCommit, diffFile.Name)
	if leftLineCount <= lastLine.LeftIdx || rightLineCount <= lastLine.RightIdx {
		return nil
	}
	tailDiffLine := &DiffLine{
		Type:    DiffLineSection,
		Content: " ",
		SectionInfo: &DiffLineSectionInfo{
			Path:         diffFile.Name,
			LastLeftIdx:  lastLine.LeftIdx,
			LastRightIdx: lastLine.RightIdx,
			LeftIdx:      leftLineCount,
			RightIdx:     rightLineCount,
		}}
	tailSection := &DiffSection{FileName: diffFile.Name, Lines: []*DiffLine{tailDiffLine}}
	return tailSection

}

func getCommitFileLineCount(commit *git.Commit, filePath string) int {
	blob, err := commit.GetBlobByPath(filePath)
	if err != nil {
		return 0
	}
	lineCount, err := blob.GetBlobLineCount()
	if err != nil {
		return 0
	}
	return lineCount
}

// Diff represents a difference between two git trees.
type Diff struct {
	NumFiles, TotalAddition, TotalDeletion int
	Files                                  []*DiffFile
	IsIncomplete                           bool
}

// LoadComments loads comments into each line
func (diff *Diff) LoadComments(issue *models.Issue, currentUser *models.User) error {
	allComments, err := models.FetchCodeComments(issue, currentUser)
	if err != nil {
		return err
	}
	for _, file := range diff.Files {
		if lineCommits, ok := allComments[file.Name]; ok {
			for _, section := range file.Sections {
				for _, line := range section.Lines {
					if comments, ok := lineCommits[int64(line.LeftIdx*-1)]; ok {
						line.Comments = append(line.Comments, comments...)
					}
					if comments, ok := lineCommits[int64(line.RightIdx)]; ok {
						line.Comments = append(line.Comments, comments...)
					}
					sort.SliceStable(line.Comments, func(i, j int) bool {
						return line.Comments[i].CreatedUnix < line.Comments[j].CreatedUnix
					})
				}
			}
		}
	}
	return nil
}

const cmdDiffHead = "diff --git "

// ParsePatch builds a Diff object from a io.Reader and some
// parameters.
// TODO: move this function to gogits/git-module
func ParsePatch(maxLines, maxLineCharacters, maxFiles int, reader io.Reader) (*Diff, error) {
	var (
		diff       = &Diff{Files: make([]*DiffFile, 0)}
		curFile    = &DiffFile{}
		curSection = &DiffSection{
			Lines: make([]*DiffLine, 0, 10),
		}

		leftLine, rightLine int
		lineCount           int
		curFileLinesCount   int
		curFileLFSPrefix    bool
	)

	input := bufio.NewReader(reader)
	isEOF := false
	for !isEOF {
		var linebuf bytes.Buffer
		for {
			b, err := input.ReadByte()
			if err != nil {
				if err == io.EOF {
					isEOF = true
					break
				} else {
					return nil, fmt.Errorf("ReadByte: %v", err)
				}
			}
			if b == '\n' {
				break
			}
			if linebuf.Len() < maxLineCharacters {
				linebuf.WriteByte(b)
			} else if linebuf.Len() == maxLineCharacters {
				curFile.IsIncomplete = true
			}
		}
		line := linebuf.String()

		if strings.HasPrefix(line, "--- ") {
			if line[4] == '"' {
				fmt.Sscanf(line[4:], "%q", &curFile.OldName)
			} else {
				curFile.OldName = line[4:]
				if strings.Contains(curFile.OldName, " ") {
					// Git adds a terminal \t if there is a space in the name
					curFile.OldName = curFile.OldName[:len(curFile.OldName)-1]
				}
			}
			if curFile.OldName[0:2] == "a/" {
				curFile.OldName = curFile.OldName[2:]
			}
			continue
		} else if strings.HasPrefix(line, "+++ ") {
			if line[4] == '"' {
				fmt.Sscanf(line[4:], "%q", &curFile.Name)
			} else {
				curFile.Name = line[4:]
				if strings.Contains(curFile.Name, " ") {
					// Git adds a terminal \t if there is a space in the name
					curFile.Name = curFile.Name[:len(curFile.Name)-1]
				}
			}
			if curFile.Name[0:2] == "b/" {
				curFile.Name = curFile.Name[2:]
			}
			curFile.IsRenamed = (curFile.Name != curFile.OldName) && !(curFile.IsCreated || curFile.IsDeleted)
			if curFile.IsDeleted {
				curFile.Name = curFile.OldName
				curFile.OldName = ""
			} else if curFile.IsCreated {
				curFile.OldName = ""
			}
			continue
		} else if len(line) == 0 {
			continue
		}

		if strings.HasPrefix(line, "+++") || strings.HasPrefix(line, "---") || len(line) == 0 {
			continue
		}

		trimLine := strings.Trim(line, "+- ")

		if trimLine == models.LFSMetaFileIdentifier {
			curFileLFSPrefix = true
		}

		if curFileLFSPrefix && strings.HasPrefix(trimLine, models.LFSMetaFileOidPrefix) {
			oid := strings.TrimPrefix(trimLine, models.LFSMetaFileOidPrefix)

			if len(oid) == 64 {
				m := &models.LFSMetaObject{Oid: oid}
				count, err := models.Count(m)

				if err == nil && count > 0 {
					curFile.IsBin = true
					curFile.IsLFSFile = true
					curSection.Lines = nil
				}
			}
		}

		curFileLinesCount++
		lineCount++

		// Diff data too large, we only show the first about maxLines lines
		if curFileLinesCount >= maxLines {
			curFile.IsIncomplete = true
		}
		switch {
		case line[0] == ' ':
			diffLine := &DiffLine{Type: DiffLinePlain, Content: line, LeftIdx: leftLine, RightIdx: rightLine}
			leftLine++
			rightLine++
			curSection.Lines = append(curSection.Lines, diffLine)
			curSection.FileName = curFile.Name
			continue
		case line[0] == '@':
			curSection = &DiffSection{}
			curFile.Sections = append(curFile.Sections, curSection)
			lineSectionInfo := getDiffLineSectionInfo(curFile.Name, line, leftLine-1, rightLine-1)
			diffLine := &DiffLine{
				Type:        DiffLineSection,
				Content:     line,
				SectionInfo: lineSectionInfo,
			}
			curSection.Lines = append(curSection.Lines, diffLine)
			curSection.FileName = curFile.Name
			// update line number.
			leftLine = lineSectionInfo.LeftIdx
			rightLine = lineSectionInfo.RightIdx
			continue
		case line[0] == '+':
			curFile.Addition++
			diff.TotalAddition++
			diffLine := &DiffLine{Type: DiffLineAdd, Content: line, RightIdx: rightLine}
			rightLine++
			curSection.Lines = append(curSection.Lines, diffLine)
			curSection.FileName = curFile.Name
			continue
		case line[0] == '-':
			curFile.Deletion++
			diff.TotalDeletion++
			diffLine := &DiffLine{Type: DiffLineDel, Content: line, LeftIdx: leftLine}
			if leftLine > 0 {
				leftLine++
			}
			curSection.Lines = append(curSection.Lines, diffLine)
			curSection.FileName = curFile.Name
		case strings.HasPrefix(line, "Binary"):
			curFile.IsBin = true
			continue
		}

		// Get new file.
		if strings.HasPrefix(line, cmdDiffHead) {
			if len(diff.Files) >= maxFiles {
				diff.IsIncomplete = true
				_, err := io.Copy(ioutil.Discard, reader)
				if err != nil {
					return nil, fmt.Errorf("Copy: %v", err)
				}
				break
			}

			curFile = &DiffFile{
				Index:    len(diff.Files) + 1,
				Type:     DiffFileChange,
				Sections: make([]*DiffSection, 0, 10),
			}
			diff.Files = append(diff.Files, curFile)
			curFileLinesCount = 0
			leftLine = 1
			rightLine = 1
			curFileLFSPrefix = false

			// Check file diff type and is submodule.
		loop:
			for {
				line, err := input.ReadString('\n')
				if err != nil {
					if err == io.EOF {
						isEOF = true
					} else {
						return nil, fmt.Errorf("ReadString: %v", err)
					}
				}

				if curFile.Type != DiffFileRename {
					switch {
					case strings.HasPrefix(line, "new file"):
						curFile.Type = DiffFileAdd
						curFile.IsCreated = true
					case strings.HasPrefix(line, "deleted"):
						curFile.Type = DiffFileDel
						curFile.IsDeleted = true
					case strings.HasPrefix(line, "index"):
						curFile.Type = DiffFileChange
					case strings.HasPrefix(line, "similarity index 100%"):
						curFile.Type = DiffFileRename
					}
					if curFile.Type > 0 && curFile.Type != DiffFileRename {
						if strings.HasSuffix(line, " 160000\n") {
							curFile.IsSubmodule = true
						}
						break
					}
				} else {
					switch {
					case strings.HasPrefix(line, "rename from "):
						if line[12] == '"' {
							fmt.Sscanf(line[12:], "%q", &curFile.OldName)
						} else {
							curFile.OldName = line[12:]
							curFile.OldName = curFile.OldName[:len(curFile.OldName)-1]
						}
					case strings.HasPrefix(line, "rename to "):
						if line[10] == '"' {
							fmt.Sscanf(line[10:], "%q", &curFile.Name)
						} else {
							curFile.Name = line[10:]
							curFile.Name = curFile.Name[:len(curFile.Name)-1]
						}
						curFile.IsRenamed = true
						break loop
					case strings.HasPrefix(line, "copy from "):
						if line[10] == '"' {
							fmt.Sscanf(line[10:], "%q", &curFile.OldName)
						} else {
							curFile.OldName = line[10:]
							curFile.OldName = curFile.OldName[:len(curFile.OldName)-1]
						}
					case strings.HasPrefix(line, "copy to "):
						if line[8] == '"' {
							fmt.Sscanf(line[8:], "%q", &curFile.Name)
						} else {
							curFile.Name = line[8:]
							curFile.Name = curFile.Name[:len(curFile.Name)-1]
						}
						curFile.IsRenamed = true
						curFile.Type = DiffFileCopy
						break loop
					default:
						if strings.HasSuffix(line, " 160000\n") {
							curFile.IsSubmodule = true
						} else {
							break loop
						}
					}
				}
			}
		}
	}

	// FIXME: detect encoding while parsing.
	var buf bytes.Buffer
	for _, f := range diff.Files {
		buf.Reset()
		for _, sec := range f.Sections {
			for _, l := range sec.Lines {
				buf.WriteString(l.Content)
				buf.WriteString("\n")
			}
		}
		charsetLabel, err := charset.DetectEncoding(buf.Bytes())
		if charsetLabel != "UTF-8" && err == nil {
			encoding, _ := stdcharset.Lookup(charsetLabel)
			if encoding != nil {
				d := encoding.NewDecoder()
				for _, sec := range f.Sections {
					for _, l := range sec.Lines {
						if c, _, err := transform.String(d, l.Content); err == nil {
							l.Content = c
						}
					}
				}
			}
		}
	}
	diff.NumFiles = len(diff.Files)
	return diff, nil
}

// GetDiffRange builds a Diff between two commits of a repository.
// passing the empty string as beforeCommitID returns a diff from the
// parent commit.
func GetDiffRange(repoPath, beforeCommitID, afterCommitID string, maxLines, maxLineCharacters, maxFiles int) (*Diff, error) {
	return GetDiffRangeWithWhitespaceBehavior(repoPath, beforeCommitID, afterCommitID, maxLines, maxLineCharacters, maxFiles, "")
}

// GetDiffRangeWithWhitespaceBehavior builds a Diff between two commits of a repository.
// Passing the empty string as beforeCommitID returns a diff from the parent commit.
// The whitespaceBehavior is either an empty string or a git flag
func GetDiffRangeWithWhitespaceBehavior(repoPath, beforeCommitID, afterCommitID string, maxLines, maxLineCharacters, maxFiles int, whitespaceBehavior string) (*Diff, error) {
	gitRepo, err := git.OpenRepository(repoPath)
	if err != nil {
		return nil, err
	}
	defer gitRepo.Close()

	commit, err := gitRepo.GetCommit(afterCommitID)
	if err != nil {
		return nil, err
	}

	// FIXME: graceful: These commands should likely have a timeout
	ctx, cancel := context.WithCancel(git.DefaultContext)
	defer cancel()
	var cmd *exec.Cmd
	if (len(beforeCommitID) == 0 || beforeCommitID == git.EmptySHA) && commit.ParentCount() == 0 {
		cmd = exec.CommandContext(ctx, git.GitExecutable, "show", afterCommitID)
	} else {
		actualBeforeCommitID := beforeCommitID
		if len(actualBeforeCommitID) == 0 {
			parentCommit, _ := commit.Parent(0)
			actualBeforeCommitID = parentCommit.ID.String()
		}
		diffArgs := []string{"diff", "-M"}
		if len(whitespaceBehavior) != 0 {
			diffArgs = append(diffArgs, whitespaceBehavior)
		}
		diffArgs = append(diffArgs, actualBeforeCommitID)
		diffArgs = append(diffArgs, afterCommitID)
		cmd = exec.CommandContext(ctx, git.GitExecutable, diffArgs...)
		beforeCommitID = actualBeforeCommitID
	}
	cmd.Dir = repoPath
	cmd.Stderr = os.Stderr

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return nil, fmt.Errorf("StdoutPipe: %v", err)
	}

	if err = cmd.Start(); err != nil {
		return nil, fmt.Errorf("Start: %v", err)
	}

	pid := process.GetManager().Add(fmt.Sprintf("GetDiffRange [repo_path: %s]", repoPath), cancel)
	defer process.GetManager().Remove(pid)

	diff, err := ParsePatch(maxLines, maxLineCharacters, maxFiles, stdout)
	if err != nil {
		return nil, fmt.Errorf("ParsePatch: %v", err)
	}
	for _, diffFile := range diff.Files {
		tailSection := diffFile.GetTailSection(gitRepo, beforeCommitID, afterCommitID)
		if tailSection != nil {
			diffFile.Sections = append(diffFile.Sections, tailSection)
		}
	}

	if err = cmd.Wait(); err != nil {
		return nil, fmt.Errorf("Wait: %v", err)
	}

	shortstatArgs := []string{beforeCommitID + "..." + afterCommitID}
	if len(beforeCommitID) == 0 || beforeCommitID == git.EmptySHA {
		shortstatArgs = []string{git.EmptyTreeSHA, afterCommitID}
	}
	diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = git.GetDiffShortStat(repoPath, shortstatArgs...)
	if err != nil && strings.Contains(err.Error(), "no merge base") {
		// git >= 2.28 now returns an error if base and head have become unrelated.
		// previously it would return the results of git diff --shortstat base head so let's try that...
		shortstatArgs = []string{beforeCommitID, afterCommitID}
		diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = git.GetDiffShortStat(repoPath, shortstatArgs...)
	}
	if err != nil {
		return nil, err
	}

	return diff, nil
}

// GetDiffCommit builds a Diff representing the given commitID.
func GetDiffCommit(repoPath, commitID string, maxLines, maxLineCharacters, maxFiles int) (*Diff, error) {
	return GetDiffRange(repoPath, "", commitID, maxLines, maxLineCharacters, maxFiles)
}

// CommentAsDiff returns c.Patch as *Diff
func CommentAsDiff(c *models.Comment) (*Diff, error) {
	diff, err := ParsePatch(setting.Git.MaxGitDiffLines,
		setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(c.Patch))
	if err != nil {
		return nil, err
	}
	if len(diff.Files) == 0 {
		return nil, fmt.Errorf("no file found for comment ID: %d", c.ID)
	}
	secs := diff.Files[0].Sections
	if len(secs) == 0 {
		return nil, fmt.Errorf("no sections found for comment ID: %d", c.ID)
	}
	return diff, nil
}

// CommentMustAsDiff executes AsDiff and logs the error instead of returning
func CommentMustAsDiff(c *models.Comment) *Diff {
	diff, err := CommentAsDiff(c)
	if err != nil {
		log.Warn("CommentMustAsDiff: %v", err)
	}
	return diff
}