Fix regexp character class syntax property ghost matching bug

The syntax-table-dependent regexp character classes [:space:],
[:word:] and [:punct:] always use the buffer-local syntax table for
performance reasons.  Fix a bug that could cause ghost (mis)matches
from use of lingering state by constructs that do use syntax
properties, such as `\sX`.

* src/regex-emacs.c (BUFFER_SYNTAX): New macro.
(ISPUNCT, ISSPACE, ISWORD): Use BUFFER_SYNTAX instead of SYNTAX.
(regex_compile): Delete syntax table setup code that is no longer
needed.
* test/src/regex-emacs-tests.el (regex-emacs-syntax-properties):
New regression test.

1 files changed, 16 insertions, 0 deletions

diff --git a/test/src/regex-emacs-tests.el b/test/src/regex-emacs-tests.el
index 08a93dbf30e..4e2c0f67a44 100644
--- a/test/src/regex-emacs-tests.el
+++ b/test/src/regex-emacs-tests.el
@@ -949,4 +949,20 @@ This evaluates the TESTS test cases from glibc."
     (should (equal (smatch "a\\=*b" "ab") 0))
     ))
 
+(ert-deftest regex-emacs-syntax-properties ()
+  ;; Verify absence of character class syntax property ghost matching bug.
+  (let ((re "\\s-[[:space:]]")
+        (s (concat "a"
+                (propertize "b" 'syntax-table '(0))  ; whitespace
+                "éz"))
+        (parse-sexp-lookup-properties t))
+    ;; Test matching in a string...
+    (should (equal (string-match re s) nil))
+    ;; ... and in a buffer.
+    (should (equal (with-temp-buffer
+                     (insert s)
+                     (goto-char (point-min))
+                     (re-search-forward re nil t))
+                   nil))))
+
 ;;; regex-emacs-tests.el ends here