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.

1 files changed, 15 insertions, 0 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