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From: Stefan Monnier <monnier <at> iro.umontreal.ca> To: Alan Mackenzie <acm <at> muc.de> Cc: 68938 <at> debbugs.gnu.org Subject: bug#68938: Emacs "master". Incorrect code generated by pcase. Date: Mon, 05 Feb 2024 13:27:21 -0500
> In a development version of Emacs, last synched with master in December,
> I have added the following pcase clause to macroexp--expand-all in
> lisp/emacs-lisp/macroexp.el:
>
> (`(,(and 'defalias d
> (guard (and (null defining-symbol)
> (symbol-with-pos-p d))))
> ',sym . ,_)
> ;; Here, don't change the form; just set `defining-symbol'
> ;; for a (defalias 'foo ...) in the source code.
> ;; (when (symbol-with-pos-p d)
> (setq defining-symbol sym)
> form)
Where did do you add it?
> .. pcase expands that clause to this cond clause:
>
> ((eq x0 'defalias)
> (cond
> ((let* ((d x0))
> (and (null defining-symbol) (symbol-with-pos-p d)))
> (let* ((x14 (cdr-safe form)))
> (cond
> ((consp x14)
> (let* ((x15 (car-safe x14)))
> (cond
> ((consp x15)
> (let* ((x16 (car-safe x15)))
> (cond
> ((eq x16 'quote)
> (let* ((x17 (cdr-safe x15)))
> (cond
> ((consp x17)
> (let* ((x18 (car-safe x17)) (x19 (cdr-safe x17)))
> (cond
> ((null x19)
> (let ((d x0) (sym x18))
> (ignore d) (setq defining-symbol sym) form))
> ((consp x0)
> (let* ((x21 (car-safe x0)))
> (if (eq x21 'lambda) (funcall pcase-3 x0 x14)
> (funcall pcase-2 x0))))
> (t (funcall pcase-2 x0)))))
> ((consp x0)
> (let* ((x23 (car-safe x0)))
> (if (eq x23 'lambda) (funcall pcase-3 x0 x14)
> (funcall pcase-2 x0))))
> (t (funcall pcase-2 x0)))))
> ((consp x0)
> (let* ((x25 (car-safe x0)))
> (if (eq x25 'lambda) (funcall pcase-3 x0 x14)
> (funcall pcase-2 x0))))
> (t (funcall pcase-2 x0)))))
> ((consp x0)
> (let* ((x27 (car-safe x0)))
> (if (eq x27 'lambda) (funcall pcase-3 x0 x14)
> (funcall pcase-2 x0))))
> (t (funcall pcase-2 x0)))))
> ((consp x0)
> (let* ((x29 (car-safe x0)))
> (if (eq x29 'lambda) (funcall pcase-3 x0 x14) (funcall pcase-2 x0))))
> (t (funcall pcase-2 x0)))))
> ((consp x0)
> (let* ((x31 (car-safe x0)))
> (if (eq x31 'lambda)
> (let* ((x33 (cdr-safe form))) (funcall pcase-3 x0 x33))
> (funcall pcase-2 x0))))
> (t (funcall pcase-2 x0))))
>
> .. This contains errors:
>
> (i) Although it has been established that x0 is 'defalias, there are many
> tests (consp x0).
Yup, clearly some missed optimization.
I added your code just before the
(`(function ,(and f `(lambda . ,_)))
branch, and I didn't see such poor code, so it seems that it depends on
further details.
On further inspection I see a similar problem in another branch,
where it generated:
((pcase--flip memq '(defconst defvar) x71)
(let* ((x78 (cdr-safe form)))
(cond
((consp x78)
(let* ((x79 (car-safe x78)))
(cond
((symbolp x79)
(let ((name x79))
(push name macroexp--dynvars)
(macroexp--all-forms form 2)))
((consp x71)
(let* ((x81 (car-safe x71)))
(if (eq x81 'lambda) (funcall pcase-2 x71 x78)
(funcall pcase-1 x71))))
(t (funcall pcase-1 x71)))))
((consp x71)
(let* ((x83 (car-safe x71)))
(if (eq x83 'lambda) (funcall pcase-2 x71 x78)
(funcall pcase-1 x71))))
(t (funcall pcase-1 x71)))))
where we do that same useless (consp x71) test. I think this case is
"normal" (the branch's test is basically (memq x71 '(defconst defvar),
i.e. more complex than (eq x71 'defalias)) and I seem to remember
consciously punting on handling such things in
`pcase--mutually-exclusive-p`.
Your case doesn't sound like one I'm aware of, OTOH.
> (ii) There are calls of the form (funcall pcase-2 x0), i.e. (funcall
> pcase-2 'defalias). This causes a wrong-number-of-arguments error.
I don't see this problem here. In my case it's
(funcall pcase-1 x71)
but the number of arguments is right since pcase-1 is defined a bit
earlier as:
(lambda (func)
(let ((handler (function-get func 'compiler-macro)))
(if (null handler) (macroexp--all-forms form 1)
(unless (functionp handler)
(with-demoted-errors "macroexp--expand-all: %S"
(autoload-do-load (indirect-function func) func)))
(let ((newform (macroexp--compiler-macro handler form)))
(if (eq form newform)
(if
(equal form
(setq newform
(macroexp--all-forms form 1)))
form
(setq form
(macroexp--compiler-macro handler newform))
(if (eq newform form) newform
(macroexp--expand-all form)))
(macroexp--expand-all newform))))))
> (iii) There is no sign of the final `form' being returned, though this
> may be being done elsewhere.
I see the following in your code sample:
(cond
((null x19)
(let ((d x0) (sym x18))
(ignore d) (setq defining-symbol sym) form))
which seems to be correctly returning `form`.
Stefan
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