Don't save bookmark context from encrypted files

* doc/emacs/regs.texi (Bookmarks): Mention this.
* lisp/bookmark.el (bookmark-make-record): Don't include context
in encrypted files (bug#57856).

* lisp/epa-hook.el (epa-file-name-p): New function.

doc/emacs/regs.texi

@@ -381,7 +381,8 @@ jump to the bookmark.
 @code{bookmark-jump} can find the proper position even if the file is
 modified slightly.  The variable @code{bookmark-search-size} says how
 many characters of context to record on each side of the bookmark's
-position.
+position.  (In buffers that are visiting encrypted files, no context
+is saved in the bookmarks file no matter the value of this variable.)
 
   Here are some additional commands for working with bookmarks:
 

etc/NEWS

@@ -180,6 +180,11 @@ of 'user-emacs-directory'.
 
 * Incompatible changes in Emacs 29.1
 
++++
+*** bookmarks no longer include context for encrypted files.
+If you're visiting an encrypted file, setting a bookmark no longer
+includes excerpts from that buffer in the bookmarks file.
+
 ---
 *** 'show-paren-mode' is now disabled in 'special-mode' buffers.
 In Emacs versions previous to Emacs 28.1, 'show-paren-mode' defaulted

lisp/bookmark.el

@@ -594,7 +594,18 @@ equivalently just return ALIST without NAME.")
 
 (defun bookmark-make-record ()
   "Return a new bookmark record (NAME . ALIST) for the current location."
-  (let ((record (funcall bookmark-make-record-function)))
+  (let* ((bookmark-search-size
+          ;; If we're in a buffer that's visiting an encrypted file,
+          ;; don't include any context in the bookmark file, because
+          ;; that would leak (possibly secret) data.
+          (if (and buffer-file-name
+                   (or (and (fboundp 'epa-file-name-p)
+                            (epa-file-name-p buffer-file-name))
+                       (and (fboundp 'tramp-crypt-file-name-p)
+                            (tramp-crypt-file-name-p buffer-file-name))))
+              0
+            bookmark-search-size))
+         (record (funcall bookmark-make-record-function)))
     ;; Set up default name if the function does not provide one.
     (unless (stringp (car record))
       (if (car record) (push nil record))

lisp/epa-hook.el

@@ -88,6 +88,10 @@ interface, update `file-name-handler-alist'."
 	   epa-file-inhibit-auto-save)
       (auto-save-mode 0)))
 
+(defun epa-file-name-p (file)
+  "Say whether FILE is handled by `epa-file'."
+  (and auto-encryption-mode (string-match-p epa-file-name-regexp file)))
+
 (define-minor-mode auto-encryption-mode
   "Toggle automatic file encryption/decryption (Auto Encryption mode)."
   :global t :init-value t :group 'epa-file :version "23.1"