Recognize single quote attribute values in nxml and sgml (Bug#35381)

* lisp/textmodes/sgml-mode.el (sgml-specials): Add single quote.
(sgml-syntax-propertize-rules): Handle single quote.
* test/lisp/nxml/nxml-mode-tests.el (nxml-mode-font-lock-quotes): New
test.
* test/lisp/textmodes/sgml-mode-tests.el
(sgml-delete-tag-bug-8203-should-not-delete-apostrophe): Now passes.

1 files changed, 15 insertions, 19 deletions

diff --git a/lisp/textmodes/sgml-mode.el b/lisp/textmodes/sgml-mode.el
index 50b2077ef4f..128e58810e5 100644
--- a/lisp/textmodes/sgml-mode.el
+++ b/lisp/textmodes/sgml-mode.el
@@ -100,24 +100,20 @@ a DOCTYPE or an XML declaration."
   :group 'sgml
   :type 'hook)
 
-;; As long as Emacs's syntax can't be complemented with predicates to context
-;; sensitively confirm the syntax of characters, we have to live with this
-;; kludgy kind of tradeoff.
-(defvar sgml-specials '(?\")
+;; The official handling of "--" is complicated in SGML, and
+;; historically not well supported by browser HTML parsers.
+;; Recommendations for writing HTML comments is to use <!--...-->
+;; (where ... doesn't contain "--") to avoid the complications
+;; altogether (XML goes even further by requiring this in the spec).
+;; So there is probably no need to handle it "correctly".
+(defvar sgml-specials '(?\" ?\')
   "List of characters that have a special meaning for SGML mode.
 This list is used when first loading the `sgml-mode' library.
-The supported characters and potential disadvantages are:
+The supported characters are ?\\\", ?\\=', and ?-.
 
-  ?\\\" Makes \" in text start a string.
-  ?\\=' Makes \\=' in text start a string.
-  ?-    Makes -- in text start a comment.
-
-When only one of ?\\\" or ?\\=' are included, \"\\='\" or \\='\"\\=', as can be found in
-DTDs, start a string.  To partially avoid this problem this also makes these
-self insert as named entities depending on `sgml-quick-keys'.
-
-Including ?- has the problem of affecting dashes that have nothing to do
-with comments, so we normally turn it off.")
+Including ?- makes double dashes into comment delimiters, but
+they are really only supposed to delimit comments within DTD
+definitions.  So we normally turn it off.")
 
 (defvar sgml-quick-keys nil
   "Use <, >, &, /, SPC and `sgml-specials' keys \"electrically\" when non-nil.
@@ -351,12 +347,12 @@ Any terminating `>' or `/' is not matched.")
      ("--[ \t\n]*\\(>\\)" (1 "> b"))
      ("\\(<\\)[?!]" (1 (prog1 "|>"
                          (sgml-syntax-propertize-inside end))))
-     ;; Double quotes outside of tags should not introduce strings.
+     ;; Quotes outside of tags should not introduce strings.
      ;; Be careful to call `syntax-ppss' on a position before the one we're
      ;; going to change, so as not to need to flush the data we just computed.
-     ("\"" (0 (if (prog1 (zerop (car (syntax-ppss (match-beginning 0))))
-                    (goto-char (match-end 0)))
-                  (string-to-syntax ".")))))))
+     ("[\"']" (0 (if (prog1 (zerop (car (syntax-ppss (match-beginning 0))))
+                       (goto-char (match-end 0)))
+                     (string-to-syntax ".")))))))
 
 (defun sgml-syntax-propertize (start end)
   "Syntactic keywords for `sgml-mode'."