bug#35186: 26.1; confusing error message and location on eager dotted pair evaluation

bug#35186: 26.1; confusing error message and location on eager dotted pair evaluation

[Ernesto Alfonso]

Originally reported on the flycheck bug tracker:

https://github.com/flycheck/flycheck/issues/1557#event-2240962448

Using a dotted pair that accidently is eagerly evaluated results in a
confusing error message and location.
    
From the flycheck tracker, fmdkdd's steps to reproduce:

    $ cat foo.el
    (defun foo ()
      (some irrelevant form)
      (a . b))
    $ emacs -Q --batch -f batch-byte-compile foo.el
    In toplevel form:
    /tmp/foo.el:1:8:Error: Wrong type argument: sequencep, b


In GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2019-04-01 built on debian-x1g4
Windowing system distributor 'The X.Org Foundation', version 11.0.11902000
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bug#35186: 26.1; confusing error message and location on eager dotted pair evaluation

[Lars Ingebrigtsen]

Ernesto Alfonso <erjoalgo@gmail.com> writes:

>     $ cat foo.el
>     (defun foo ()
>       (some irrelevant form)
>       (a . b))
>     $ emacs -Q --batch -f batch-byte-compile foo.el
>     In toplevel form:
>     /tmp/foo.el:1:8:Error: Wrong type argument: sequencep, b

That's not an optimal error message; no.

I've been trying to find out what part of the byte compiler/reader
machinery is outputting it, but I haven't found it -- does anybody else
know where this is coming from?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#35186: 26.1; confusing error message and location on eager dotted pair evaluation

[Michael Heerdegen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> I've been trying to find out what part of the byte compiler/reader
> machinery is outputting it, but I haven't found it -- does anybody else
> know where this is coming from?

AFAICT it comes from these lines (line 776 and following) in
`cconv-analyze-form' in cconv.el:

#+begin_src emacs-lisp
    (`(,_ . ,body-forms)    ; First element is a function or whatever.
     (dolist (form body-forms) (cconv-analyze-form form env)))
#+end_src

It's not an explicit error but just dolist barfing.

Michael.

bug#35186: 26.1; confusing error message and location on eager dotted pair evaluation

[Lars Ingebrigtsen]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> AFAICT it comes from these lines (line 776 and following) in
> `cconv-analyze-form' in cconv.el:
>
> #+begin_src emacs-lisp
>     (`(,_ . ,body-forms)    ; First element is a function or whatever.
>      (dolist (form body-forms) (cconv-analyze-form form env)))
> #+end_src
>
> It's not an explicit error but just dolist barfing.

I've tried sprinkling some messaging liberally over cconv-analyze-form,
and I'm unable to make it trigger in the test case.  It does seem likely
that the error is from a dolist somewhere, but it seems to happen before
we get to that function...

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#35186: 26.1; confusing error message and location on eager dotted pair evaluation

[Michael Heerdegen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> I've tried sprinkling some messaging liberally over cconv-analyze-form,
> and I'm unable to make it trigger in the test case.  It does seem likely
> that the error is from a dolist somewhere, but it seems to happen before
> we get to that function...

Did you enable lexical-binding mode?  I guess it will make a difference.
A had done it AFAIR.

Michael.

bug#35186: 26.1; confusing error message and location on eager dotted pair evaluation

[Lars Ingebrigtsen]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> Lars Ingebrigtsen <larsi@gnus.org> writes:
>
>> I've tried sprinkling some messaging liberally over cconv-analyze-form,
>> and I'm unable to make it trigger in the test case.  It does seem likely
>> that the error is from a dolist somewhere, but it seems to happen before
>> we get to that function...
>
> Did you enable lexical-binding mode?  I guess it will make a difference.
> A had done it AFAIR.

Ah, yes, that made a difference.  With the following patch I get:

larsi@xo:~/src/emacs/trunk$ emake ; ./src/emacs -Q --batch -f batch-byte-compile /tmp/r.el
  ELC      emacs-lisp/cconv.elc

In toplevel form:
/tmp/r.el:3:1: Error: Wrong type argument: proper-list-p, (a . b)

Does this makes sense to everybody?

diff --git a/lisp/emacs-lisp/cconv.el b/lisp/emacs-lisp/cconv.el
index 351a097ad1..c024cda876 100644
--- a/lisp/emacs-lisp/cconv.el
+++ b/lisp/emacs-lisp/cconv.el
@@ -750,6 +750,8 @@ cconv-analyze-form
     ;; (`(declare . ,_) nil)               ;The args don't contain code.
 
     (`(,_ . ,body-forms)    ; First element is a function or whatever.
+     (unless (listp body-forms)
+       (signal 'wrong-type-argument (list 'proper-list-p form)))
      (dolist (form body-forms) (cconv-analyze-form form env)))
 
     ((pred symbolp)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#35186: 26.1; confusing error message and location on eager dotted pair evaluation

[Lars Ingebrigtsen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> Does this makes sense to everybody?

There wasn't any response in a year, but the change doesn't seem to lead
to any regressions, and it fixes the reported issue, so I've now pushed
it to Emacs 28.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no