bug#64391: buffer narrowing slowdown regression in emacs 29

[Gregory Heytings <gregory@heytings.org>]

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Thanks for your feedback!

>
> I have one question about the new `with-restriction` macro: if it is 
> intended as a convenience macro for unlabelled narrowing as well, 
> shouldn't it then expand to the obvious
>
>  (save-restriction
>    (narrow-to-region BEG END)
>    BODY)
>
> instead the much more expensive call to a helper function?
>

Yes.  In fact now that we have a separate function for the labeled case, 
we can remove the funcall in both cases.  Patch attached.

>
> The documentation should also make it clear that `nil` is not a valid 
> label.
>

Is that not already clear in the docstring, which says "in which LABEL is 
a symbol"?

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From 4897d6ade80e9928b7f25d0fb6f970c4975c43bd Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Fri, 7 Jul 2023 09:54:32 +0000
Subject: [PATCH] Simplify 'with-restriction' and 'without-restriction'

* lisp/subr.el (with-restriction, without-restriction): Merge the
bodies of the 'internal--with-restriction' and
'internal--without-restriction' function into the macros.  The
result is more efficient than a funcall.
(internal--with-restriction, internal--without-restriction):
Remove.
---
 lisp/subr.el | 26 ++++++--------------------
 1 file changed, 6 insertions(+), 20 deletions(-)

diff --git a/lisp/subr.el b/lisp/subr.el
index 85adef5b689..42a6cfec514 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -3973,16 +3973,10 @@ with-restriction
 \(fn START END [:label LABEL] BODY)"
   (declare (indent 2) (debug t))
   (if (eq (car rest) :label)
-      `(internal--with-restriction ,start ,end (lambda () ,@(cddr rest))
-                                 ,(cadr rest))
-    `(internal--with-restriction ,start ,end (lambda () ,@rest))))
-
-(defun internal--with-restriction (start end body &optional label)
-  "Helper function for `with-restriction', which see."
-  (save-restriction
-    (narrow-to-region start end)
-    (if label (internal--label-restriction label))
-    (funcall body)))
+      `(save-restriction
+         (internal--labeled-narrow-to-region ,start ,end ,(cadr rest))
+         ,@(cddr rest))
+    `(save-restriction (narrow-to-region ,start ,end) ,@rest)))
 
 (defmacro without-restriction (&rest rest)
   "Execute BODY without restrictions.
@@ -3996,16 +3990,8 @@ without-restriction
 \(fn [:label LABEL] BODY)"
   (declare (indent 0) (debug t))
   (if (eq (car rest) :label)
-      `(internal--without-restriction (lambda () ,@(cddr rest))
-                                    ,(cadr rest))
-    `(internal--without-restriction (lambda () ,@rest))))
-
-(defun internal--without-restriction (body &optional label)
-  "Helper function for `without-restriction', which see."
-  (save-restriction
-    (if label (internal--unlabel-restriction label))
-    (widen)
-    (funcall body)))
+      `(save-restriction (internal--labeled-widen ,(cadr rest)) ,@(cddr rest))
+    `(save-restriction (widen) ,@rest)))
 
 (defun find-tag-default-bounds ()
   "Determine the boundaries of the default tag, based on text at point.
-- 
2.39.2