Improve errors & warnings due to fancy quoted vars (Bug#32939)

Add some hints to the message for byte compiler free & unused variable
warnings, and 'void-variable' errors where the variable has confusable
quote characters in it.
* lisp/help.el (uni-confusables), uni-confusables-regexp): New
constants.
(help-command-error-confusable-suggestions): New function, added to
`command-error-function'.
(help-uni-confusable-suggestions): New function.
* lisp/emacs-lisp/bytecomp.el (byte-compile-variable-ref):
* lisp/emacs-lisp/cconv.el (cconv--analyze-use): Use it.

* lisp/emacs-lisp/lisp-mode.el
(lisp--match-confusable-symbol-character): New function.
(lisp-fdefs): Use it to fontify confusable characters with
font-lock-warning-face when they occur in symbol names.
* doc/lispref/modes.texi (Faces for Font Lock):
* doc/lispref/objects.texi (Basic Char Syntax): Recommend backslash
escaping of confusable characters, and mention new fontification.
* etc/NEWS: Announce the new fontification behavior.
* test/lisp/emacs-lisp/lisp-mode-tests.el (lisp-fontify-confusables):
New test.

1 files changed, 26 insertions, 0 deletions

diff --git a/test/lisp/emacs-lisp/lisp-mode-tests.el b/test/lisp/emacs-lisp/lisp-mode-tests.el
index e4ba929ecbd..c0dd68c0a0b 100644
--- a/test/lisp/emacs-lisp/lisp-mode-tests.el
+++ b/test/lisp/emacs-lisp/lisp-mode-tests.el
@@ -20,6 +20,10 @@
 (require 'ert)
 (require 'cl-lib)
 (require 'lisp-mode)
+(require 'faceup)
+
+
+;;; Indentation
 
 (defconst lisp-mode-tests--correctly-indented-sexp "\
 \(a
@@ -290,5 +294,27 @@ Expected initialization file: `%s'\"
     (insert "\"\n")
     (lisp-indent-region (point-min) (point-max))))
 
+
+;;; Fontification
+
+(ert-deftest lisp-fontify-confusables ()
+  "Unescaped 'smart quotes' should be fontified in `font-lock-warning-face'."
+  (with-temp-buffer
+    (dolist (ch
+             '(#x2018 ;; LEFT SINGLE QUOTATION MARK
+               #x2019 ;; RIGHT SINGLE QUOTATION MARK
+               #x201B ;; SINGLE HIGH-REVERSED-9 QUOTATION MARK
+               #x201C ;; LEFT DOUBLE QUOTATION MARK
+               #x201D ;; RIGHT DOUBLE QUOTATION MARK
+               #x201F ;; DOUBLE HIGH-REVERSED-9 QUOTATION MARK
+               #x301E ;; DOUBLE PRIME QUOTATION MARK
+               #xFF02 ;; FULLWIDTH QUOTATION MARK
+               #xFF07 ;; FULLWIDTH APOSTROPHE
+               ))
+      (insert (format "«w:%c»foo \\%cfoo\n" ch ch)))
+    (let ((faceup (buffer-string)))
+      (faceup-clean-buffer)
+      (should (faceup-test-font-lock-buffer 'emacs-lisp-mode faceup)))))
+
 (provide 'lisp-mode-tests)
 ;;; lisp-mode-tests.el ends here