bug#46912: 28.0.50; Byte compiled defvar with lexical binding throws (void-variable foo)

[Pip Cet <pipcet@gmail.com>]

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On Thu, Mar 4, 2021 at 8:48 PM Lars Ingebrigtsen <larsi@gnus.org> wrote:
> Joseph Mingrone <jrm@ftfl.ca> writes:
> > I think the problem was introduced before 9b4a2dd (2021-02-14).  That
> > was the last snapshot that I was running and I'm pretty sure I saw the
> > problem then.  If I can find time tonight, I'll try to confirm that.
>
> Great; bisecting this would be very helpful.

Absolutely.

> Pip Cet <pipcet@gmail.com> writes:
>
> > I can reproduce it, three, but I can also reproduce it with the change
> > I think you're referring to reverted.
>
> Sorry about that; it was a stab in the dark using the "the one who
> touched it last" principle.  :-/

Not a problem at all. In fact, I've taken a look and it seems
byte-optimize-form-code-walker simply ignores the value form in a
defvar now..

So I suspect it's commit 83983b6b7a115474572973b62eb5e42251713e63, I'm
cc'ing Mattias, and I suspect this patch might help (but I've only
done one quick test).

Pip

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From c39ecf1c053f551a4b384d2ad2994fe0e58d67b0 Mon Sep 17 00:00:00 2001
From: Pip Cet <pipcet@gmail.com>
Date: Thu, 4 Mar 2021 21:06:13 +0000
Subject: [PATCH] Don't ignore lexically-bound variables in a defvar
 (bug#46912)

* lisp/emacs-lisp/byte-opt.el (byte-optimize-form-code-walker): Walk
the value form of a defvar.
---
 lisp/emacs-lisp/byte-opt.el | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index b51ba801552d6..ba2165a5d59ce 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -607,7 +607,9 @@ byte-optimize-form-code-walker
            (setq args (cddr args)))
          (cons fn (nreverse var-expr-list))))
 
-      (`(defvar ,(and (pred symbolp) name) . ,_)
+      (`(defvar ,(and (pred symbolp) name) . ,rest)
+       (when rest
+         (byte-optimize-form (car rest) nil))
        (push name byte-optimize--dynamic-vars)
        form)
 
-- 
2.30.1