Fix sgml-mode handling of quotes within parens (Bug#36347)

* lisp/textmodes/sgml-mode.el (sgml-syntax-propertize): Use
syntax-ppss-table if set.  This is only needed on the release branch,
on master the caller (syntax-propertize) already does this.
(sgml-mode): Set syntax-ppss-table to sgml-tag-syntax-table.  This
correctly classifies parens as punctuation, so they won't confuse the
parser.
* test/lisp/textmodes/sgml-mode-tests.el (sgml-tests--quotes-syntax):
New test copied from master, with two cases added for this bug.

lisp/textmodes/sgml-mode.el

@@ -357,10 +357,11 @@ Any terminating `>' or `/' is not matched.")
 (defun sgml-syntax-propertize (start end)
   "Syntactic keywords for `sgml-mode'."
   (goto-char start)
-  (sgml-syntax-propertize-inside end)
-  (funcall
-   (syntax-propertize-rules sgml-syntax-propertize-rules)
-   start end))
+  (with-syntax-table (or syntax-ppss-table (syntax-table))
+    (sgml-syntax-propertize-inside end)
+    (funcall
+     (syntax-propertize-rules sgml-syntax-propertize-rules)
+     start end)))
 
 (defun sgml-syntax-propertize-inside (end)
   (let ((ppss (syntax-ppss)))
@@ -568,6 +569,7 @@ Do \\[describe-key] on the following bindings to discover what they do.
 			      sgml-font-lock-keywords-2)
 			     nil t))
   (setq-local syntax-propertize-function #'sgml-syntax-propertize)
+  (setq-local syntax-ppss-table sgml-tag-syntax-table)
   (setq-local facemenu-add-face-function 'sgml-mode-facemenu-add-face-function)
   (setq-local sgml-xml-mode (sgml-xml-guess))
   (unless sgml-xml-mode

test/lisp/textmodes/sgml-mode-tests.el

@@ -130,5 +130,27 @@ The point is set to the beginning of the buffer."
    (sgml-delete-tag 1)
    (should (string= "Winter is comin'" (buffer-string)))))
 
+(ert-deftest sgml-tests--quotes-syntax ()
+  (dolist (str '("a\"b <t>c'd</t>"
+                 "a'b <t>c\"d</t>"
+                 "<t>\"a'</t>"
+                 "<t>'a\"</t>"
+                 "<t>\"a'\"</t>"
+                 "<t>'a\"'</t>"
+                 "a\"b <tag>c'd</tag>"
+                 ;;"<tag>c>'d</tag>" Fixed in master.
+                 "<t><!-- \" --></t>"
+                 "<t><!-- ' --></t>"
+                 "<t>(')</t>"
+                 "<t>(\")</t>"
+                 ))
+   (with-temp-buffer
+     (sgml-mode)
+     (insert str)
+     (ert-info ((format "%S" str) :prefix "Test case: ")
+       ;; Check that last tag is parsed as a tag.
+       (should (= 1 (car (syntax-ppss (1- (point-max))))))
+       (should (= 0 (car (syntax-ppss (point-max)))))))))
+
 (provide 'sgml-mode-tests)
 ;;; sgml-mode-tests.el ends here