Add customizable to display raw bytes as hex

* src/xdisp.c (get_next_display_element): Dispatch used format string
for unprintables based on new display-raw-bytes-as-hex variable.
(display-raw-bytes-as-hex): New variable.  (Bug#27122)

* lisp/cus-start.el: Add defcustom form for display-raw-bytes-as-hex.

* doc/emacs/display.texi: Document the new variable.
* etc/NEWS: Mention display-raw-bytes-as-hex.

* test/manual/redisplay-testsuite.el (test-redisplay-5-toggle)
(test-redisplay-5): New tests.
(test-redisplay): Call test-redisplay-5.

1 files changed, 26 insertions, 1 deletions

diff --git a/test/manual/redisplay-testsuite.el b/test/manual/redisplay-testsuite.el
index 694d55ab1db..2175cbab1b7 100644
--- a/test/manual/redisplay-testsuite.el
+++ b/test/manual/redisplay-testsuite.el
@@ -34,7 +34,8 @@
     (setq overlay (make-overlay opoint (point)))
     (while props
       (overlay-put overlay (car props) (cadr props))
-      (setq props (cddr props)))))
+      (setq props (cddr props)))
+    overlay))
 
 (defun test-redisplay-1 ()
   (insert "Test 1: Displaying adjacent and overlapping overlays:\n\n")
@@ -293,6 +294,29 @@ static unsigned char x_bits[] = {0xff, 0x81, 0xbd, 0xa5, 0xa5, 0xbd, 0x81, 0xff
 
   (insert "\n"))
 
+(defvar test-redisplay-5-expected-overlay nil)
+(defvar test-redisplay-5-result-overlay nil)
+
+(defun test-redisplay-5-toggle (_event)
+  (interactive "e")
+  (setq display-raw-bytes-as-hex (not display-raw-bytes-as-hex))
+  (let ((label (if display-raw-bytes-as-hex "\\x80" "\\200")))
+    (overlay-put test-redisplay-5-expected-overlay 'display
+                 (propertize label 'face 'escape-glyph))))
+
+(defun test-redisplay-5 ()
+  (insert "Test 5: Display of raw bytes:\n\n")
+  (insert "  Expected: ")
+  (setq test-redisplay-5-expected-overlay
+        (test-insert-overlay " " 'display
+                             (propertize "\\200" 'face 'escape-glyph)))
+  (insert "\n    Result: ")
+  (setq test-redisplay-5-result-overlay
+        (test-insert-overlay " " 'display "\200"))
+  (insert "\n\n")
+  (insert-button "Toggle between octal and hex display"
+                 'action 'test-redisplay-5-toggle))
+
 
 (defun test-redisplay ()
   (interactive)
@@ -309,5 +333,6 @@ static unsigned char x_bits[] = {0xff, 0x81, 0xbd, 0xa5, 0xa5, 0xbd, 0x81, 0xff
     (test-redisplay-2)
     (test-redisplay-3)
     (test-redisplay-4)
+    (test-redisplay-5)
     (goto-char (point-min))))