Make warning about unescaped character literals more helpful.

See Bug#31676.

* lisp/emacs-lisp/byte-run.el
(byte-run--unescaped-character-literals-warning): New defun.

* src/lread.c (load_warn_unescaped_character_literals): Use new defun.
(syms_of_lread): Define symbol for new defun.

* lisp/emacs-lisp/bytecomp.el (byte-compile-from-buffer): Use new
defun.

* test/src/lread-tests.el (lread-tests--unescaped-char-literals):
test/lisp/emacs-lisp/bytecomp-tests.el
(bytecomp-tests--unescaped-char-literals): Adapt unit tests.

2 files changed, 18 insertions, 8 deletions

diff --git a/lisp/emacs-lisp/byte-run.el b/lisp/emacs-lisp/byte-run.el
index b638b56be1f..7e256f83272 100644
--- a/lisp/emacs-lisp/byte-run.el
+++ b/lisp/emacs-lisp/byte-run.el
@@ -495,6 +495,21 @@ is enabled."
   (car (last body)))
 
 
+(defun byte-run--unescaped-character-literals-warning ()
+  "Return a warning about unescaped character literals.
+If there were any unescaped character literals in the last form
+read, return an appropriate warning message as a string.
+Otherwise, return nil.  For internal use only."
+  ;; This is called from lread.c and therefore needs to be preloaded.
+  (if lread--unescaped-character-literals
+      (let ((sorted (sort lread--unescaped-character-literals #'<)))
+        (format-message "unescaped character literals %s detected, %s expected!"
+                        (mapconcat (lambda (char) (format "`?%c'" char))
+                                   sorted ", ")
+                        (mapconcat (lambda (char) (format "`?\\%c'" char))
+                                   sorted ", ")))))
+
+
 ;; I nuked this because it's not a good idea for users to think of using it.
 ;; These options are a matter of installation preference, and have nothing to
 ;; with particular source files; it's a mistake to suggest to users
diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 8bbe6292d9d..4c61e1a4471 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -2082,14 +2082,9 @@ With argument ARG, insert value in current buffer after the form."
 		 (not (eobp)))
 	  (setq byte-compile-read-position (point)
 		byte-compile-last-position byte-compile-read-position)
-	  (let* ((lread--unescaped-character-literals nil)
-                 (form (read inbuffer)))
-            (when lread--unescaped-character-literals
-              (byte-compile-warn
-               "unescaped character literals %s detected!"
-               (mapconcat (lambda (char) (format "`?%c'" char))
-                          (sort lread--unescaped-character-literals #'<)
-                          ", ")))
+	  (let ((form (read inbuffer))
+                (warning (byte-run--unescaped-character-literals-warning)))
+            (when warning (byte-compile-warn "%s" warning))
 	    (byte-compile-toplevel-file-form form)))
 	;; Compile pending forms at end of file.
 	(byte-compile-flush-pending)