Subject: Re: bug#58082: recent whitespace-mode regression for read-only buffers

From: Richard Hansen <[email-masked]>
Date: Mon, 26 Sep 2022 19:21:50 -0400

Good catch Kyle, and thank you for the fix Lars.

Attached are a couple of patches that add a test case.
From eb8e5828d3fb6917943b4f81a20a1584d3c784d9 Mon Sep 17 00:00:00 2001
From: Richard Hansen <[email-masked]>
Date: Mon, 26 Sep 2022 17:07:52 -0400
Subject: [PATCH 1/2] ert-x: Improve realism of `ert-with-test-buffer-selected'

* lisp/emacs-lisp/ert-x.el (ert-with-test-buffer-selected): Set
`inhibit-read-only' and `buffer-read-only' to nil when executing the
body to provide a more realistic test environment.
---
 lisp/emacs-lisp/ert-x.el | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/ert-x.el b/lisp/emacs-lisp/ert-x.el
index f00f1b33d7..bfd796586d 100644
--- a/lisp/emacs-lisp/ert-x.el
+++ b/lisp/emacs-lisp/ert-x.el
@@ -126,7 +126,15 @@ ert-with-test-buffer-selected
                  (body-function
                   . ,(lambda (window)
                        (select-window window t)
-                       (let ((inhibit-modification-hooks nil))
+                       ;; body-function is intended to initialize the
+                       ;; contents of a temporary read-only buffer, so
+                       ;; it is executed with some convenience
+                       ;; changes.  Undo those changes so that the
+                       ;; test buffer behaves more like an ordinary
+                       ;; buffer while the body executes.
+                       (let ((inhibit-modification-hooks nil)
+                             (inhibit-read-only nil)
+                             (buffer-read-only nil))
                          (setq ,ret (progn ,@body))))))
              nil))
          ,ret))))
-- 
2.37.3

From 69b39ff80b227ab2f4d37ec292a30b11bd367243 Mon Sep 17 00:00:00 2001
From: Richard Hansen <[email-masked]>
Date: Mon, 26 Sep 2022 02:12:41 -0400
Subject: [PATCH 2/2] ; whitespace: Add test case for read-only buffers
 (bug#58082)

---
 test/lisp/whitespace-tests.el | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/test/lisp/whitespace-tests.el b/test/lisp/whitespace-tests.el
index 97c30c4d62..fb53543c9e 100644
--- a/test/lisp/whitespace-tests.el
+++ b/test/lisp/whitespace-tests.el
@@ -27,7 +27,8 @@
 (defmacro whitespace-tests--with-test-buffer (style &rest body)
   "Run BODY in a buffer with `whitespace-mode' style STYLE.
 The buffer is displayed in `selected-window', and
-`noninteractive' is set to nil even in batch mode."
+`noninteractive' is set to nil even in batch mode.  If STYLE is
+nil, `whitespace-mode' is left disabled."
   (declare (debug ((style form) def-body))
            (indent 1))
   `(ert-with-test-buffer-selected ()
@@ -37,7 +38,8 @@ whitespace-tests--with-test-buffer
      (let ((noninteractive nil)
            (whitespace-style ,style))
        (font-lock-mode 1)
-       (whitespace-mode 1)
+       ,(when style
+          '(whitespace-mode 1))
        ,@body)))
 
 (defun whitespace-tests--faceup (&rest lines)
@@ -310,6 +312,21 @@ whitespace-tests--empty-eob
                                       "\t\n"
                                       " »"))))
 
+(ert-deftest whitespace-tests--empty-bob-eob-read-only-buffer ()
+  (whitespace-tests--with-test-buffer '()
+    (insert "\nx\n\n")
+    (should (equal (buffer-string) "\nx\n\n"))
+    (setq-local buffer-read-only t)
+    (goto-char 2)
+    (should (equal (line-number-at-pos) 2))
+    (should (equal (- (point) (line-beginning-position)) 0))
+    (let ((whitespace-style '(face empty)))
+      (whitespace-mode 1)
+      (should (whitespace-tests--faceup "«:whitespace-empty:\n"
+                                        "»x\n"
+                                        "«:whitespace-empty:\n"
+                                        "»")))))
+
 (provide 'whitespace-tests)
 
 ;;; whitespace-tests.el ends here
-- 
2.37.3