From 1631735f2738ee7bdf751c92b462d976a7119f99 Mon Sep 17 00:00:00 2001
From: Juri Linkov <juri@linkov.net>
Date: Wed, 28 May 2025 20:15:21 +0300
Subject: [PATCH] * lisp/isearch.el (search-within-boundaries): Optimize
 (bug#78520).

For non-subregexp case, search for the first match and continue
from its position.  This avoids unnecessary scan for all text properties
until the first match.  When nothing is found, skip the entire body.

(cherry picked from commit 295f73d23d337593959ec7d73ecbcfa61a732f0f)
---
 lisp/isearch.el | 41 +++++++++++++++++++++++++++--------------
 1 file changed, 27 insertions(+), 14 deletions(-)

diff --git a/lisp/isearch.el b/lisp/isearch.el
index cfb6f4c50a3..fb32731709a 100644
--- a/lisp/isearch.el
+++ b/lisp/isearch.el
@@ -4570,9 +4570,7 @@ defaults to the value of `isearch-search-fun-default' when nil."
 (defun search-within-boundaries ( search-fun get-fun next-fun
                                   string &optional bound noerror count)
   (let* ((old (point))
-         ;; Check if point is already on the property.
-         (beg (when (funcall get-fun old) old))
-         end found (i 0)
+         beg end found skip (i 0)
          (subregexp
           (and isearch-regexp
                (save-match-data
@@ -4582,18 +4580,33 @@ defaults to the value of `isearch-search-fun-default' when nil."
                      (when (subregexp-context-p string (match-beginning 0))
                        ;; The ^/$ is not inside a char-range or escaped.
                        (throw 'subregexp t))))))))
-    ;; Otherwise, try to search for the next property.
-    (unless beg
-      (setq beg (funcall next-fun old))
-      (when beg
-        (if (or (null bound)
-                (if isearch-forward
-                    (< beg bound)
-                  (> beg bound)))
-            (goto-char beg)
-          (setq beg nil))))
+
+    ;; Optimization for non-subregexp case to set the initial position
+    ;; on the first match assuming there is no need to check boundaries
+    ;; for a search string/regexp without anchors (bug#78520).
+    (unless subregexp
+      (save-match-data
+        (if (funcall (or search-fun (isearch-search-fun-default))
+                     string bound noerror count)
+            (goto-char (if isearch-forward (match-beginning 0) (match-end 0)))
+          (setq skip t))))
+
+    (unless skip
+      ;; Check if point is already on the property.
+      (setq beg (when (funcall get-fun (point)) (point)))
+      ;; Otherwise, try to search for the next property.
+      (unless beg
+        (setq beg (funcall next-fun (point)))
+        (when beg
+          (if (or (null bound)
+                  (if isearch-forward
+                      (< beg bound)
+                    (> beg bound)))
+              (goto-char beg)
+            (setq beg nil)))))
+
     ;; Non-nil `beg' means there are more properties.
-    (while (and beg (not found))
+    (while (and beg (not found) (not skip))
       ;; Search for the end of the current property.
       (setq end (funcall next-fun beg))
       ;; Handle ^/$ specially by matching in a temporary buffer.
-- 
2.39.5