1 files changed, 345 insertions, 0 deletions
diff --git a/modules/git/repo_compare.go b/modules/git/repo_compare.go
new file mode 100644
index 00000000..b6e9d2b4
--- /dev/null
+++ b/modules/git/repo_compare.go
@@ -0,0 +1,345 @@
+// Copyright 2015 The Gogs Authors. All rights reserved.
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+
+	logger "code.gitea.io/gitea/modules/log"
+)
+
+// CompareInfo represents needed information for comparing references.
+type CompareInfo struct {
+	MergeBase    string
+	BaseCommitID string
+	HeadCommitID string
+	Commits      []*Commit
+	NumFiles     int
+}
+
+// GetMergeBase checks and returns merge base of two branches and the reference used as base.
+func (repo *Repository) GetMergeBase(tmpRemote, base, head string) (string, string, error) {
+	if tmpRemote == "" {
+		tmpRemote = "origin"
+	}
+
+	if tmpRemote != "origin" {
+		tmpBaseName := RemotePrefix + tmpRemote + "/tmp_" + base
+		// Fetch commit into a temporary branch in order to be able to handle commits and tags
+		_, _, err := NewCommand(repo.Ctx, "fetch", "--no-tags").AddDynamicArguments(tmpRemote).AddDashesAndList(base + ":" + tmpBaseName).RunStdString(&RunOpts{Dir: repo.Path})
+		if err == nil {
+			base = tmpBaseName
+		}
+	}
+
+	stdout, _, err := NewCommand(repo.Ctx, "merge-base").AddDashesAndList(base, head).RunStdString(&RunOpts{Dir: repo.Path})
+	return strings.TrimSpace(stdout), base, err
+}
+
+// GetCompareInfo generates and returns compare information between base and head branches of repositories.
+func (repo *Repository) GetCompareInfo(basePath, baseBranch, headBranch string, directComparison, fileOnly bool) (_ *CompareInfo, err error) {
+	var (
+		remoteBranch string
+		tmpRemote    string
+	)
+
+	// We don't need a temporary remote for same repository.
+	if repo.Path != basePath {
+		// Add a temporary remote
+		tmpRemote = strconv.FormatInt(time.Now().UnixNano(), 10)
+		if err = repo.AddRemote(tmpRemote, basePath, false); err != nil {
+			return nil, fmt.Errorf("AddRemote: %w", err)
+		}
+		defer func() {
+			if err := repo.RemoveRemote(tmpRemote); err != nil {
+				logger.Error("GetPullRequestInfo: RemoveRemote: %v", err)
+			}
+		}()
+	}
+
+	compareInfo := new(CompareInfo)
+
+	compareInfo.HeadCommitID, err = GetFullCommitID(repo.Ctx, repo.Path, headBranch)
+	if err != nil {
+		compareInfo.HeadCommitID = headBranch
+	}
+
+	compareInfo.MergeBase, remoteBranch, err = repo.GetMergeBase(tmpRemote, baseBranch, headBranch)
+	if err == nil {
+		compareInfo.BaseCommitID, err = GetFullCommitID(repo.Ctx, repo.Path, remoteBranch)
+		if err != nil {
+			compareInfo.BaseCommitID = remoteBranch
+		}
+		separator := "..."
+		baseCommitID := compareInfo.MergeBase
+		if directComparison {
+			separator = ".."
+			baseCommitID = compareInfo.BaseCommitID
+		}
+
+		// We have a common base - therefore we know that ... should work
+		if !fileOnly {
+			// avoid: ambiguous argument 'refs/a...refs/b': unknown revision or path not in the working tree. Use '--': 'git <command> [<revision>...] -- [<file>...]'
+			var logs []byte
+			logs, _, err = NewCommand(repo.Ctx, "log").AddArguments(prettyLogFormat).
+				AddDynamicArguments(baseCommitID + separator + headBranch).AddArguments("--").
+				RunStdBytes(&RunOpts{Dir: repo.Path})
+			if err != nil {
+				return nil, err
+			}
+			compareInfo.Commits, err = repo.parsePrettyFormatLogToList(logs)
+			if err != nil {
+				return nil, fmt.Errorf("parsePrettyFormatLogToList: %w", err)
+			}
+		} else {
+			compareInfo.Commits = []*Commit{}
+		}
+	} else {
+		compareInfo.Commits = []*Commit{}
+		compareInfo.MergeBase, err = GetFullCommitID(repo.Ctx, repo.Path, remoteBranch)
+		if err != nil {
+			compareInfo.MergeBase = remoteBranch
+		}
+		compareInfo.BaseCommitID = compareInfo.MergeBase
+	}
+
+	// Count number of changed files.
+	// This probably should be removed as we need to use shortstat elsewhere
+	// Now there is git diff --shortstat but this appears to be slower than simply iterating with --nameonly
+	compareInfo.NumFiles, err = repo.GetDiffNumChangedFiles(remoteBranch, headBranch, directComparison)
+	if err != nil {
+		return nil, err
+	}
+	return compareInfo, nil
+}
+
+type lineCountWriter struct {
+	numLines int
+}
+
+// Write counts the number of newlines in the provided bytestream
+func (l *lineCountWriter) Write(p []byte) (n int, err error) {
+	n = len(p)
+	l.numLines += bytes.Count(p, []byte{'\000'})
+	return n, err
+}
+
+// GetDiffNumChangedFiles counts the number of changed files
+// This is substantially quicker than shortstat but...
+func (repo *Repository) GetDiffNumChangedFiles(base, head string, directComparison bool) (int, error) {
+	// Now there is git diff --shortstat but this appears to be slower than simply iterating with --nameonly
+	w := &lineCountWriter{}
+	stderr := new(bytes.Buffer)
+
+	separator := "..."
+	if directComparison {
+		separator = ".."
+	}
+
+	// avoid: ambiguous argument 'refs/a...refs/b': unknown revision or path not in the working tree. Use '--': 'git <command> [<revision>...] -- [<file>...]'
+	if err := NewCommand(repo.Ctx, "diff", "-z", "--name-only").AddDynamicArguments(base + separator + head).AddArguments("--").
+		Run(&RunOpts{
+			Dir:    repo.Path,
+			Stdout: w,
+			Stderr: stderr,
+		}); err != nil {
+		if strings.Contains(stderr.String(), "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 -z --name-only base head so let's try that...
+			w = &lineCountWriter{}
+			stderr.Reset()
+			if err = NewCommand(repo.Ctx, "diff", "-z", "--name-only").AddDynamicArguments(base, head).AddArguments("--").Run(&RunOpts{
+				Dir:    repo.Path,
+				Stdout: w,
+				Stderr: stderr,
+			}); err == nil {
+				return w.numLines, nil
+			}
+		}
+		return 0, fmt.Errorf("%w: Stderr: %s", err, stderr)
+	}
+	return w.numLines, nil
+}
+
+// GetDiffShortStat counts number of changed files, number of additions and deletions
+func (repo *Repository) GetDiffShortStat(base, head string) (numFiles, totalAdditions, totalDeletions int, err error) {
+	numFiles, totalAdditions, totalDeletions, err = GetDiffShortStat(repo.Ctx, repo.Path, nil, base+"..."+head)
+	if err != nil && strings.Contains(err.Error(), "no merge base") {
+		return GetDiffShortStat(repo.Ctx, repo.Path, nil, base, head)
+	}
+	return numFiles, totalAdditions, totalDeletions, err
+}
+
+// GetDiffShortStat counts number of changed files, number of additions and deletions
+func GetDiffShortStat(ctx context.Context, repoPath string, trustedArgs TrustedCmdArgs, dynamicArgs ...string) (numFiles, totalAdditions, totalDeletions int, err error) {
+	// Now if we call:
+	// $ git diff --shortstat 1ebb35b98889ff77299f24d82da426b434b0cca0...788b8b1440462d477f45b0088875
+	// we get:
+	// " 9902 files changed, 2034198 insertions(+), 298800 deletions(-)\n"
+	cmd := NewCommand(ctx, "diff", "--shortstat").AddArguments(trustedArgs...).AddDynamicArguments(dynamicArgs...)
+	stdout, _, err := cmd.RunStdString(&RunOpts{Dir: repoPath})
+	if err != nil {
+		return 0, 0, 0, err
+	}
+
+	return parseDiffStat(stdout)
+}
+
+var shortStatFormat = regexp.MustCompile(
+	`\s*(\d+) files? changed(?:, (\d+) insertions?\(\+\))?(?:, (\d+) deletions?\(-\))?`)
+
+var patchCommits = regexp.MustCompile(`^From\s(\w+)\s`)
+
+func parseDiffStat(stdout string) (numFiles, totalAdditions, totalDeletions int, err error) {
+	if len(stdout) == 0 || stdout == "\n" {
+		return 0, 0, 0, nil
+	}
+	groups := shortStatFormat.FindStringSubmatch(stdout)
+	if len(groups) != 4 {
+		return 0, 0, 0, fmt.Errorf("unable to parse shortstat: %s groups: %s", stdout, groups)
+	}
+
+	numFiles, err = strconv.Atoi(groups[1])
+	if err != nil {
+		return 0, 0, 0, fmt.Errorf("unable to parse shortstat: %s. Error parsing NumFiles %w", stdout, err)
+	}
+
+	if len(groups[2]) != 0 {
+		totalAdditions, err = strconv.Atoi(groups[2])
+		if err != nil {
+			return 0, 0, 0, fmt.Errorf("unable to parse shortstat: %s. Error parsing NumAdditions %w", stdout, err)
+		}
+	}
+
+	if len(groups[3]) != 0 {
+		totalDeletions, err = strconv.Atoi(groups[3])
+		if err != nil {
+			return 0, 0, 0, fmt.Errorf("unable to parse shortstat: %s. Error parsing NumDeletions %w", stdout, err)
+		}
+	}
+	return numFiles, totalAdditions, totalDeletions, err
+}
+
+// GetDiffOrPatch generates either diff or formatted patch data between given revisions
+func (repo *Repository) GetDiffOrPatch(base, head string, w io.Writer, patch, binary bool) error {
+	if patch {
+		return repo.GetPatch(base, head, w)
+	}
+	if binary {
+		return repo.GetDiffBinary(base, head, w)
+	}
+	return repo.GetDiff(base, head, w)
+}
+
+// GetDiff generates and returns patch data between given revisions, optimized for human readability
+func (repo *Repository) GetDiff(base, head string, w io.Writer) error {
+	return NewCommand(repo.Ctx, "diff", "-p").AddDynamicArguments(base, head).Run(&RunOpts{
+		Dir:    repo.Path,
+		Stdout: w,
+	})
+}
+
+// GetDiffBinary generates and returns patch data between given revisions, including binary diffs.
+func (repo *Repository) GetDiffBinary(base, head string, w io.Writer) error {
+	return NewCommand(repo.Ctx, "diff", "-p", "--binary", "--histogram").AddDynamicArguments(base, head).Run(&RunOpts{
+		Dir:    repo.Path,
+		Stdout: w,
+	})
+}
+
+// GetPatch generates and returns format-patch data between given revisions, able to be used with `git apply`
+func (repo *Repository) GetPatch(base, head string, w io.Writer) error {
+	stderr := new(bytes.Buffer)
+	err := NewCommand(repo.Ctx, "format-patch", "--binary", "--stdout").AddDynamicArguments(base + "..." + head).
+		Run(&RunOpts{
+			Dir:    repo.Path,
+			Stdout: w,
+			Stderr: stderr,
+		})
+	if err != nil && bytes.Contains(stderr.Bytes(), []byte("no merge base")) {
+		return NewCommand(repo.Ctx, "format-patch", "--binary", "--stdout").AddDynamicArguments(base, head).
+			Run(&RunOpts{
+				Dir:    repo.Path,
+				Stdout: w,
+			})
+	}
+	return err
+}
+
+// GetFilesChangedBetween returns a list of all files that have been changed between the given commits
+// If base is undefined empty SHA (zeros), it only returns the files changed in the head commit
+// If base is the SHA of an empty tree (EmptyTreeSHA), it returns the files changes from the initial commit to the head commit
+func (repo *Repository) GetFilesChangedBetween(base, head string) ([]string, error) {
+	objectFormat, err := repo.GetObjectFormat()
+	if err != nil {
+		return nil, err
+	}
+	cmd := NewCommand(repo.Ctx, "diff-tree", "--name-only", "--root", "--no-commit-id", "-r", "-z")
+	if base == objectFormat.EmptyObjectID().String() {
+		cmd.AddDynamicArguments(head)
+	} else {
+		cmd.AddDynamicArguments(base, head)
+	}
+	stdout, _, err := cmd.RunStdString(&RunOpts{Dir: repo.Path})
+	if err != nil {
+		return nil, err
+	}
+	split := strings.Split(stdout, "\000")
+
+	// Because Git will always emit filenames with a terminal NUL ignore the last entry in the split - which will always be empty.
+	if len(split) > 0 {
+		split = split[:len(split)-1]
+	}
+
+	return split, err
+}
+
+// GetDiffFromMergeBase generates and return patch data from merge base to head
+func (repo *Repository) GetDiffFromMergeBase(base, head string, w io.Writer) error {
+	stderr := new(bytes.Buffer)
+	err := NewCommand(repo.Ctx, "diff", "-p", "--binary").AddDynamicArguments(base + "..." + head).
+		Run(&RunOpts{
+			Dir:    repo.Path,
+			Stdout: w,
+			Stderr: stderr,
+		})
+	if err != nil && bytes.Contains(stderr.Bytes(), []byte("no merge base")) {
+		return repo.GetDiffBinary(base, head, w)
+	}
+	return err
+}
+
+// ReadPatchCommit will check if a diff patch exists and return stats
+func (repo *Repository) ReadPatchCommit(prID int64) (commitSHA string, err error) {
+	// Migrated repositories download patches to "pulls" location
+	patchFile := fmt.Sprintf("pulls/%d.patch", prID)
+	loadPatch, err := os.Open(filepath.Join(repo.Path, patchFile))
+	if err != nil {
+		return "", err
+	}
+	defer loadPatch.Close()
+	// Read only the first line of the patch - usually it contains the first commit made in patch
+	scanner := bufio.NewScanner(loadPatch)
+	scanner.Scan()
+	// Parse the Patch stats, sometimes Migration returns a 404 for the patch file
+	commitSHAGroups := patchCommits.FindStringSubmatch(scanner.Text())
+	if len(commitSHAGroups) != 0 {
+		commitSHA = commitSHAGroups[1]
+	} else {
+		return "", errors.New("patch file doesn't contain valid commit ID")
+	}
+	return commitSHA, nil
+}