bug#21695: 25.0.50; Change most occurrences of `setq' in Emacs manual to `customize-set-variable'? Really?

[Gregory Heytings <gregory@heytings.org>]

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I updated the patch with some documentation.

Is there any chance that it gets applied?

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From ea9eeb65d6514c11ae9d0ac5c4fad36213e303f9 Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Sun, 12 Sep 2021 08:19:25 +0000
Subject: [PATCH] Warn when custom variable is wrongly set.

* src/eval.c (Fsetq): Display warning when a custom variable with a :set
property is set with setq.  Warnings are displayed only for custom variables
whose files have been loaded and that have a :set property.  No warnings are
displayed for custom variables whose files have merely been preloaded,
for custom variables that do not have a :set property, and for non-custom
variables.  See bug#21695.

* etc/NEWS: Document the warning.

* doc/emacs/custom.texi: Mention the warning.
---
 doc/emacs/custom.texi | 3 ++-
 etc/NEWS              | 6 ++++++
 src/eval.c            | 9 ++++++++-
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/doc/emacs/custom.texi b/doc/emacs/custom.texi
index 9220a2078f..1b7e7d9361 100644
--- a/doc/emacs/custom.texi
+++ b/doc/emacs/custom.texi
@@ -2378,7 +2378,8 @@ do that; to enable the mode in your init file, call the minor mode
 command.  Finally, a few customizable user options are initialized in
 complex ways, and these have to be set either via the customize
 interface (@pxref{Customization}) or by using
-@code{customize-set-variable} (@pxref{Examining}).
+@code{customize-set-variable} (@pxref{Examining}).  If such options
+are inadvertently set with @code{setq}, a warning is displayed.
 
   The second argument to @code{setq} is an expression for the new
 value of the variable.  This can be a constant, a variable, or a
diff --git a/etc/NEWS b/etc/NEWS
index ca269aabaa..dfdd925ec5 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -3401,6 +3401,12 @@ truncating precision field, such as "%.2a".
 Such mixes are always signs that the outer lexical binding was an
 error and should have used dynamic binding instead.
 
+--
+** 'setq' displays a warning when 'customize-set-variable' should have been used.
+Some custom variables need to be set with 'customize-set-variable', because
+they were designed to be set through the Customization interface and have a
+:set lambda form which does other things after they have been set.
+
 ---
 ** New variable 'inhibit-mouse-event-check'.
 If bound to non-nil, a command with '(interactive "e")' doesn't signal
diff --git a/src/eval.c b/src/eval.c
index 48104bd0f4..168a7749a0 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -525,8 +525,15 @@ usage: (setq [SYM VAL]...)  */)
 	   : Qnil);
       if (!NILP (lex_binding))
 	XSETCDR (lex_binding, val); /* SYM is lexically bound.  */
-      else
+      else {
+	if (!NILP (Fget (sym, intern ("custom-set"))))
+	  call2 (intern ("display-warning"), intern ("setq"),
+		 CALLN (Fformat,
+			build_string
+			("`%s' should be set with `customize-set-variable'"),
+			sym));
 	Fset (sym, val);	/* SYM is dynamically bound.  */
+      }
     }
 
   return val;
-- 
2.33.0