Subject: bug#64919: 28.2; jsonrpc.el: jsonrpc-lambda failed to deal with single value

From: Yue Yi <[email-masked]>
Date: Sat, 29 Jul 2023 01:59:09 +0900

Currently I'm trying to write an toturial about using JSON-RPC in
Emacs, so I spent some time to read the source code and document and
found #bug64888.

Here is another bug I find: When I do a async request through
`jsonrpc-async-request' without specifing :success-fn, emacs will
signal an error. Here is the code I use:

---

(defclass yy-rpc (jsonrpc-connection)

  ((place

    :initarg :place

    :accessor yy-place)))

(cl-defmethod jsonrpc-connection-send ((conn yy-rpc)

                                 &key id method params result error)

  (setcar (yy-place conn)

          (append (if id `(:id ,id))

                 (if method `(:method ,method))

                 (if params `(:params ,params))

                 (if result `(:result ,result))

                 (if error  `(:error  ,error)))))

(setq a (cons nil nil))

(setq b (yy-rpc :name "1" :place a))

(jsonrpc-async-request b "add" [1 2])

(jsonrpc-connection-receive b '(:result 3 :id 1))

---

I just make a very simple subclass `yy-rpc' and response to it "by
hand", after evaluating the above code, I get:

---

Debugger entered--Lisp error: (wrong-type-argument listp 3)

---

By reading the code of `jsonrpc--async-request-1', I find the default
:success-fn callback uses the macro jsonrpc-lambda and I know why it
happened:

---

(funcall (jsonrpc-lambda (&rest _ignored) nil) 3)

=> Debugger entered--Lisp error: (wrong-type-argument listp 3)

---

It seems that `jsonrpc-lambda' cannot handle single value. Maybe We
can change its last line from

`(lambda (,e) (apply (cl-function (lambda ,cl-lambda-list ,@body)) ,e))))

to

`(lambda (,e) (apply (cl-function (lambda ,cl-lambda-list ,@body)) ,e ())))

After change it and M-x eval-buffer, I can get the right behavior
using the code above.

Is it the right way?

Regards

YI YUE