Fine tune diff highlighting (#36592)

modules/git/catfile_batch_reader.go

@@ -12,11 +12,15 @@ import (
 	"math"
 	"strconv"
 	"strings"
+	"sync/atomic"
+	"time"
 
 	"code.gitea.io/gitea/modules/git/gitcmd"
 	"code.gitea.io/gitea/modules/log"
 )
 
+var catFileBatchDebugWaitClose atomic.Int64
+
 type catFileBatchCommunicator struct {
 	cancel      context.CancelFunc
 	reqWriter   io.Writer
@@ -36,7 +40,14 @@ func newCatFileBatch(ctx context.Context, repoPath string, cmdCatFile *gitcmd.Co
 	ctx, ctxCancel := context.WithCancelCause(ctx)
 
 	// We often want to feed the commits in order into cat-file --batch, followed by their trees and subtrees as necessary.
-	stdinWriter, stdoutReader, pipeClose := cmdCatFile.MakeStdinStdoutPipe()
+	stdinWriter, stdoutReader, stdPipeClose := cmdCatFile.MakeStdinStdoutPipe()
+	pipeClose := func() {
+		if delay := catFileBatchDebugWaitClose.Load(); delay > 0 {
+			time.Sleep(time.Duration(delay)) // for testing purpose only
+		}
+		stdPipeClose()
+	}
+
 	ret = &catFileBatchCommunicator{
 		debugGitCmd: cmdCatFile,
 		cancel:      func() { ctxCancel(nil) },