bug#60066: 30.0.50; whitespace-mode modifies buffer

[Richard Hansen <rhansen@rhansen.org>]

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Control: tags -1 patch

The attached patch should fix this bug.

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From e23e8e7c7c6458dcaebed8d34bcaee9f818521ce Mon Sep 17 00:00:00 2001
From: Richard Hansen <rhansen@rhansen.org>
Date: Sun, 18 Dec 2022 23:04:00 -0500
Subject: [PATCH] whitespace: Fix unintended change in buffer modification
 status

* lisp/whitespace.el (whitespace--empty-at-bob-matcher,
whitespace--empty-at-eob-matcher, whitespace--update-bob-eob):
Silently add the `font-lock-multiline' text property when highlighting
beginning-of-buffer and end-of-buffer empty lines to prevent Emacs
from running modification hooks or considering the buffer to be
modified (Bug#60066).
* test/lisp/whitespace-tests.el (whitespace-tests--empty-bob-eob-modified):
Add a regression test.
---
 lisp/whitespace.el            | 28 ++++++++++++++++------------
 test/lisp/whitespace-tests.el | 11 +++++++++++
 2 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/lisp/whitespace.el b/lisp/whitespace.el
index 2c1520ec6a..558be1841a 100644
--- a/lisp/whitespace.el
+++ b/lisp/whitespace.el
@@ -2283,10 +2283,11 @@ whitespace--empty-at-bob-matcher
                 (save-excursion (goto-char whitespace-point)
                                 (line-beginning-position)))))
     (when (= p 1)
-      ;; See the comment in `whitespace--update-bob-eob' for why this
-      ;; text property is added here.
-      (put-text-property 1 whitespace-bob-marker
-                         'font-lock-multiline t))
+      (with-silent-modifications
+        ;; See the comment in `whitespace--update-bob-eob' for why
+        ;; this text property is added here.
+        (put-text-property 1 whitespace-bob-marker
+                           'font-lock-multiline t)))
     (when (< p e)
       (set-match-data (list p e))
       (goto-char e))))
@@ -2307,10 +2308,11 @@ whitespace--empty-at-eob-matcher
 empty lines will no longer be EoB empty lines.  Highlighting
 those lines can be distracting.)"
   (when (= limit (1+ (buffer-size)))
-    ;; See the comment in `whitespace--update-bob-eob' for why this
-    ;; text property is added here.
-    (put-text-property whitespace-eob-marker limit
-                       'font-lock-multiline t))
+    (with-silent-modifications
+      ;; See the comment in `whitespace--update-bob-eob' for why this
+      ;; text property is added here.
+      (put-text-property whitespace-eob-marker limit
+                         'font-lock-multiline t)))
   (let ((b (max (point) whitespace-eob-marker
                 whitespace-bob-marker ; See comment in the bob func.
                 (save-excursion (goto-char whitespace-point)
@@ -2452,8 +2454,9 @@ whitespace--update-bob-eob
             (save-match-data
               (when (looking-at whitespace-empty-at-bob-regexp)
                 (set-marker whitespace-bob-marker (match-end 1))
-                (put-text-property (match-beginning 1) (match-end 1)
-                                   'font-lock-multiline t))))
+                (with-silent-modifications
+                  (put-text-property (match-beginning 1) (match-end 1)
+                                     'font-lock-multiline t)))))
           (when (or (null end)
                     (>= end (save-excursion
                               (goto-char whitespace-eob-marker)
@@ -2466,8 +2469,9 @@ whitespace--update-bob-eob
               (when (whitespace--looking-back
                      whitespace-empty-at-eob-regexp)
                 (set-marker whitespace-eob-marker (match-beginning 1))
-                (put-text-property (match-beginning 1) (match-end 1)
-                                   'font-lock-multiline t)))))))))
+                (with-silent-modifications
+                  (put-text-property (match-beginning 1) (match-end 1)
+                                     'font-lock-multiline t))))))))))
 
 \f
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
diff --git a/test/lisp/whitespace-tests.el b/test/lisp/whitespace-tests.el
index 330fc335ea..7079c1ea5e 100644
--- a/test/lisp/whitespace-tests.el
+++ b/test/lisp/whitespace-tests.el
@@ -334,6 +334,17 @@ whitespace-tests--empty-bob-eob-read-only-buffer
                                         "«:whitespace-empty:\n"
                                         "»")))))
 
+(ert-deftest whitespace-tests--empty-bob-eob-modified ()
+  "Regression test for Bug#60066."
+  (whitespace-tests--with-test-buffer '()
+    (insert "\nx\n\n")
+    (goto-char 2)
+    (set-buffer-modified-p nil)
+    (let ((whitespace-style '(face empty)))
+      (whitespace-mode 1)
+      (should (not (buffer-modified-p))))))
+
+
 (ert-deftest whitespace-tests--indirect-clone-breaks-base-markers ()
   "Specific regression test for Bug#59618."
   (whitespace-tests--with-test-buffer '(face empty)
-- 
2.39.0


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