The cause was an unexpanded pcase-defmacro in cl-loaddefs.
* lisp/emacs-lisp/autoload.el (make-autoload):
Treat pcase-defmacro like defmacro.
((and (memq car '(easy-mmode-define-global-mode define-global-minor-mode
define-globalized-minor-mode defun defmacro
easy-mmode-define-minor-mode define-minor-mode
- define-inline cl-defun cl-defmacro cl-defgeneric))
+ define-inline cl-defun cl-defmacro cl-defgeneric
+ pcase-defmacro))
(macrop car)
(setq expand (let ((load-file-name file)) (macroexpand form)))
(memq (car expand) '(progn prog1 defalias)))