Fix issue with DiffIndex on initial commit

Unfortunately go-gitea#11614 introduced a bug whereby the initial commit of a
repository could not be seen due to there being no parent commit to
create a clear diff from.

Here we ensure that the index is empty by referring to a non-existent
file and the create a diffstat from the difference between it and the
parentless SHA.

Fix go-gitea#11650

Signed-off-by: Andrew Thornton <[email protected]>

Author: zeripath

modules/git/repo_compare.go

@@ -122,11 +122,11 @@ func (repo *Repository) GetDiffNumChangedFiles(base, head string) (int, error) {
 
 // GetDiffShortStat counts number of changed files, number of additions and deletions
 func (repo *Repository) GetDiffShortStat(base, head string) (numFiles, totalAdditions, totalDeletions int, err error) {
-	return GetDiffShortStat(repo.Path, base+"..."+head)
+	return GetDiffShortStat(nil, repo.Path, base+"..."+head)
 }
 
 // GetDiffShortStat counts number of changed files, number of additions and deletions
-func GetDiffShortStat(repoPath string, args ...string) (numFiles, totalAdditions, totalDeletions int, err error) {
+func GetDiffShortStat(env []string, repoPath string, args ...string) (numFiles, totalAdditions, totalDeletions int, err error) {
 	// Now if we call:
 	// $ git diff --shortstat 1ebb35b98889ff77299f24d82da426b434b0cca0...788b8b1440462d477f45b0088875
 	// we get:
@@ -136,7 +136,7 @@ func GetDiffShortStat(repoPath string, args ...string) (numFiles, totalAdditions
 		"--shortstat",
 	}, args...)
 
-	stdout, err := NewCommand(args...).RunInDir(repoPath)
+	stdout, err := NewCommand(args...).RunInDirWithEnv(repoPath, env)
 	if err != nil {
 		return 0, 0, 0, err
 	}

modules/repofiles/temp_repo.go

@@ -299,7 +299,7 @@ func (t *TemporaryUploadRepository) DiffIndex() (*gitdiff.Diff, error) {
 			t.repo.FullName(), err, stderr)
 	}
 
-	diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = git.GetDiffShortStat(t.basePath, "--cached", "HEAD")
+	diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = git.GetDiffShortStat(nil, t.basePath, "--cached", "HEAD")
 	if err != nil {
 		return nil, err
 	}

services/gitdiff/gitdiff.go

@@ -17,6 +17,7 @@ import (
 	"net/url"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"sort"
 	"strconv"
 	"strings"
@@ -664,7 +665,7 @@ func GetDiffRangeWithWhitespaceBehavior(repoPath, beforeCommitID, afterCommitID
 	ctx, cancel := context.WithCancel(git.DefaultContext)
 	defer cancel()
 	var cmd *exec.Cmd
-	if len(beforeCommitID) == 0 && commit.ParentCount() == 0 {
+	if (len(beforeCommitID) == 0 || beforeCommitID == git.EmptySHA) && commit.ParentCount() == 0 {
 		cmd = exec.CommandContext(ctx, git.GitExecutable, "show", afterCommitID)
 	} else {
 		actualBeforeCommitID := beforeCommitID
@@ -711,7 +712,21 @@ func GetDiffRangeWithWhitespaceBehavior(repoPath, beforeCommitID, afterCommitID
 		return nil, fmt.Errorf("Wait: %v", err)
 	}
 
-	diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = git.GetDiffShortStat(repoPath, beforeCommitID+"..."+afterCommitID)
+	shortstatArgs := []string{beforeCommitID + "..." + afterCommitID}
+	var env []string
+	if len(beforeCommitID) == 0 || beforeCommitID == git.EmptySHA {
+		shortstatArgs = []string{"--cached", afterCommitID}
+		tmpDir, err := ioutil.TempDir("", "gitdiff")
+		if err != nil {
+			return nil, err
+		}
+		defer func() {
+			_ = os.RemoveAll(tmpDir)
+		}()
+		env = append(os.Environ(), "GIT_INDEX_FILE="+filepath.Join(tmpDir, "non-existent-index"))
+
+	}
+	diff.NumFiles, diff.TotalAddition, diff.TotalDeletion, err = git.GetDiffShortStat(env, repoPath, shortstatArgs...)
 	if err != nil {
 		return nil, err
 	}