Refactor git command context & pipeline (#36406)

Less and simpler code, fewer bugs

modules/git/grep.go

@@ -77,9 +77,7 @@ func GrepSearch(ctx context.Context, repo *Repository, search string, opts GrepO
 	var stdoutReader io.ReadCloser
 	err := cmd.WithDir(repo.Path).
 		WithStdoutReader(&stdoutReader).
-		WithPipelineFunc(func(ctx context.Context, cancel context.CancelFunc) error {
-			defer stdoutReader.Close()
-
+		WithPipelineFunc(func(ctx gitcmd.Context) error {
 			isInBlock := false
 			rd := bufio.NewReaderSize(stdoutReader, util.IfZero(opts.MaxLineLength, 16*1024))
 			var res *GrepResult
@@ -105,8 +103,7 @@ func GrepSearch(ctx context.Context, repo *Repository, search string, opts GrepO
 				}
 				if line == "" {
 					if len(results) >= opts.MaxResultLimit {
-						cancel()
-						break
+						return ctx.CancelWithCause(nil)
 					}
 					isInBlock = false
 					continue