This is a MNWE:

(import (except (scheme base)
        define-syntax
        let-syntax
        letrec-syntax
        syntax-rules))
(import (srfi 147))
(import (srfi 147 er-macro-transformer))

(define-syntax unhygienic-transformer
  (syntax-rules ()
    ((unhygienic-transformer transformer)
     (er-macro-transformer
      (lambda (expr rename compare)
    (transformer expr))))))

(define-syntax bar-transformer
  (unhygienic-transformer
   (lambda (expr)
     '(unhygienic-transformer
       (lambda (expr)
     ''bar)))))

(define-syntax bar
  (bar-transformer))

Am Mi., 31. Aug. 2022 um 13:02 Uhr schrieb Marc Nieper-Wißkirchen
<xxxxxx@nieper-wisskirchen.de>:
>
> Note: The problem lies in the Chibi-specific part of SRFI 147's
> implementation, which used to work with Chibi. I haven't yet found the
> time to investigate the issue in detail.
>
> Am Mi., 31. Aug. 2022 um 11:11 Uhr schrieb Vladimir Nikishkin
> <xxxxxx@gmail.com>:
> >
> > I recently tried to learn how em-syntax-rules work, because they seem
> > like a really good idea. However, even though there is a special
> > "cond-expand" for Chibi, the version at least as late as
> > 2aa6dc829eea7c972b80ab740e073f3755bd8504 seems to have some
> > er-macro-transformer-related incompatibility.
> >
> > I am not good enough in macrology to find out where the problem lies,
> > so I would like to ask more experienced colleagues for help.
> >
> > --
> > Yours sincerely, Vladimir Nikishkin
> > (Sent from GMail web interface.)