Backport Emacs-29.1 functionality to Emacs-28.2

README.org

@@ -196,8 +196,9 @@ that *Emacs is a self-documenting editor.*
 :CUSTOM_ID: sec:init-file-header
 :END:
 
-The =user-init-file= header requires =cl-lib= and customizes Emacs variables.
+The =user-init-file= header requires =cl-lib=, backports new functions in
-It consists of four parts in listing [[lst:1st-custom-set-variables-call]],
+Emacs-29.1 to Emacs-28.2, and customizes Emacs variables.  It consists of five
+parts in listing [[lst:backport-header]], [[lst:1st-custom-set-variables-call]],
 [[lst:2nd-custom-set-variables-call]], [[lst:3rd-custom-set-variables-call]], and
 [[lst:4th-custom-set-variables-call]] in order to limit the length of the listings
 for exporting to LaTeX.
@@ -213,15 +214,49 @@ example]].
 The [[info:emacs#Init File][init file (info)]] does not load the ~custom-file~ as [[info:emacs#Saving Customizations][saving customizations
 (info)]] recommends because of the ~custom-set-variables~ function calls.
 
-#+caption[Customize the first set of Emacs variables]:
+#+caption[Header with backport of Emacs-29.1 functionality]:
-#+caption: Customize the first set of Emacs variables.
+#+caption: Header with backport of Emacs-29.1 functionality.
-#+name: lst:1st-custom-set-variables-call
+#+name: lst:backport-header
 #+begin_src emacs-lisp
 ;;; init.el --- user init file                    -*- lexical-binding: t -*-
 ;;; Commentary:
 ;;; Code:
 (require 'cl-lib)
 
+(when (version< emacs-version "29.0.0")
+  (defmacro setopt (&rest pairs)
+    "Set VARIABLE/VALUE pairs, and return the final VALUE.
+This is like `setq', but is meant for user options instead of
+plain variables.  This means that `setopt' will execute any
+`custom-set' form associated with VARIABLE.
+
+\(fn [VARIABLE VALUE]...)"
+    (declare (debug setq))
+    (unless (zerop (mod (length pairs) 2))
+      (error "PAIRS must have an even number of variable/value members"))
+    (let ((expr nil))
+      (while pairs
+        (unless (symbolp (car pairs))
+          (error "Attempting to set a non-symbol: %s" (car pairs)))
+        (push `(setopt--set ',(car pairs) ,(cadr pairs))
+              expr)
+        (setq pairs (cddr pairs)))
+      (macroexp-progn (nreverse expr))))
+
+  (defun setopt--set (variable value)
+    (custom-load-symbol variable)
+    ;; Check that the type is correct.
+    (when-let ((type (get variable 'custom-type)))
+      (unless (widget-apply (widget-convert type) :match value)
+        (warn "Value `%S' does not match type %s" value type)))
+    (put variable 'custom-check-value (list value))
+    (funcall (or (get variable 'custom-set) #'set-default) variable value)))
+#+end_src
+
+#+caption[Customize the first set of Emacs variables]:
+#+caption: Customize the first set of Emacs variables.
+#+name: lst:1st-custom-set-variables-call
+#+begin_src emacs-lisp
 (custom-set-variables
  '(after-save-hook #'executable-make-buffer-file-executable-if-script-p)
  '(column-number-mode t)
@@ -4293,10 +4328,7 @@ src_emacs-lisp{(describe-function 'inferior-emacs-lisp-mode)}.
 #+name: lst:setup-ielm
 #+begin_src emacs-lisp
 (with-eval-after-load 'ielm
-  (if (version< "29.0.0" emacs-version)
+  (setopt ielm-dynamic-return nil))
-      (setopt ielm-dynamic-return nil)
-    (custom-set-variables
-     '(ielm-dynamic-return nil))))
 #+end_src
 
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