Signal an error for the regexp "[:alnum:]"

Omitting the extra brackets is a common mistake; see discussion at
https://lists.gnu.org/archive/html/emacs-devel/2020-02/msg00215.html

* src/regex-emacs.c (reg_errcode_t, re_error_msgid): Add REG_ECLASSBR.
(regex_compile): Check for the mistake.
* test/src/regex-emacs-tests.el (regexp-invalid): Test.
* etc/NEWS: Announce.

1 files changed, 5 insertions, 0 deletions

diff --git a/test/src/regex-emacs-tests.el b/test/src/regex-emacs-tests.el
index f9372e37b11..661d416e6a7 100644
--- a/test/src/regex-emacs-tests.el
+++ b/test/src/regex-emacs-tests.el
@@ -803,4 +803,9 @@ This evaluates the TESTS test cases from glibc."
   (should-not (string-match "å" "\xe5"))
   (should-not (string-match "[å]" "\xe5")))
 
+(ert-deftest regexp-invalid ()
+  ;; relint suppression: Duplicated
+  (should-error (string-match "[:space:]" "")
+                :type 'invalid-regexp))
+
 ;;; regex-emacs-tests.el ends here