bug#68113: Wrong error message triggered in cl--generic-standard-method-combination

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

>> I don't know why you're not getting that expansion, and I don't know
>> either why you're getting that
>
>>     (signal 'wrong-type-argument (list 'symbolp 'mets-by-qual))
>
> I don't know, either.  :-(  As I say, I've tried instrumenting the `setq'
> handling code in macroexp--expand-all, but haven't managed to get
> anything pertinent output.

Ah, indeed instead of `gv-delay-error` it could also come from
`macroexp--expand-all`.
The `macroexp.el` hunk below would rule that out, tho.

>> AFAICT this weird code is likely generated by `gv-delay-error` but
>> according to `grep` it's only used in `map-elt` so I can't see why it's
>> showing up here.
>
>> I'd start debugging this with something like `M-x trace-function RET
>> gv-get RET` and `M-x debug-on-entry RET gv-delay-error RET`.
>> [ Tho, presumably you're seeing this during the bootstrap, so you'll
>>   probably want to add `message/debug` calls in the code instead.  ]
>
> I am indeed seeing this in bootstrap, so it's message and a bit of prin1.

Did you get to see the offending code in one of the outputs of `gv-get`?
Hpw 'bout a test that tries to see when that code is generated, as in
the `gv.el` patch below?


        Stefan


diff --git a/lisp/emacs-lisp/macroexp.el b/lisp/emacs-lisp/macroexp.el
index 78601c0648e..5c461206820 100644
--- a/lisp/emacs-lisp/macroexp.el
+++ b/lisp/emacs-lisp/macroexp.el
@@ -467,10 +467,10 @@ macroexp--expand-all
                                        ,var
                                      (signal 'setting-constant (list ',var))))
                                  ((symbolp var)
-                                  `(signal 'setting-constant (list ',var)))
+                                  (signal 'setting-constant (list var)))
                                  (t
-                                  `(signal 'wrong-type-argument
-                                           (list 'symbolp ',var))))
+                                  (signal 'wrong-type-argument
+                                          (list 'symbolp var))))
                                 nil 'compile-only var))))
                        (push assignment assignments))
                      (setq args (cddr args)))


diff --git a/lisp/emacs-lisp/gv.el b/lisp/emacs-lisp/gv.el
index 9f40c1f3c93..9cfd6d4b423 100644
--- a/lisp/emacs-lisp/gv.el
+++ b/lisp/emacs-lisp/gv.el
@@ -86,6 +86,8 @@ gv-get
 with a (not necessarily copyable) Elisp expression that returns the value to
 set it to.
 DO must return an Elisp expression."
+  (message "Entering gv-get for %S" place)
+  (let ((res
   (cond
    ((symbolp place)
     (let ((me (macroexpand-1 place macroexpand-all-environment)))
@@ -118,7 +120,13 @@ gv-get
                 (let* ((setter (gv-setter head)))
                   (gv--defsetter head (lambda (&rest args) `(,setter ,@args))
                                  do (cdr place))))
-            (gv-get me do))))))))
+            (gv-get me do)))))))
+  ))
+   (if (string-match-p "(list 'symbolp 'mets-by-qual)"
+        (prin1-to-string res))
+    (error "Gotcha!?"))
+   (message "Exiting gv-get for %S: %S" place res)
+   res))
 
 (defun gv-setter (name)
   ;; The name taken from Scheme's SRFI-17.  Actually, for SRFI-17, the argument