Subject: Re: bug#78608: 31.0.50; Todo mode bug revealed by setq-default change

From: Stefan Monnier <[email-masked]>
Date: Wed, 28 May 2025 11:05:08 -0400

> Stefan, I think this means we need to call out this change in NEWS as
> an incompatible change (unless you think there's a bug in that change
> which needs to be fixed, and will make this change compatible).

Would the patch below be OK?
Or should I add a link to https://xkcd.com/1172/ ?  🙂

        Stefan

diff --git a/etc/NEWS b/etc/NEWS
index 33b042720b5..1bbad5a2e5e 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2139,6 +2139,14 @@ enabled for files named "go.work".
 
 * Incompatible Lisp Changes in Emacs 31.1
 
+** 'setq-local' computes the value before making the variable local.
+The previous code made the variable buffer local before
+computing the value to assign to it.
+This bug fix is a subtle change to the semantics which should make
+no difference to the vast majority of uses but can occasionally affect
+code in surprising ways if the computation of the value refers to the
+variable.
+
 ** Nested backquotes are not supported any more in Pcase patterns.
 
 ---