xml: Properly handle symbol-qnames for attribute parsing

* lisp/xml.el (xml-parse-attlist): Do not strip 'symbol-qnames from
  xml-ns argument (reverts aea67018) (Bug#26533).
  (xml-maybe-do-ns): Properly handle default namespace by not
  interning new symbol when 'special' flag is set.

* tests/lisp/xml-tests.el (xml-parse-test--namespace-attribute-qnames)
  (xml-parse-namespace-attribute-qnames): Add test for Bug#26533.

lisp/xml.el

@@ -437,6 +437,7 @@ in the XML-NS argument."
                                  (if symbol-qnames (cdr xml-ns) xml-ns)))
                      "")))
 	(if (and symbol-qnames
+                 (not special)
 		 (not (string= prefix "xmlns")))
 	    (intern (concat ns lname))
 	  (cons ns (if special "" lname))))
@@ -646,10 +647,8 @@ surpassed `xml-entity-expansion-limit'"))))
 (defun xml-parse-attlist (&optional xml-ns)
   "Return the attribute-list after point.
 Leave point at the first non-blank character after the tag."
-  (let* ((attlist ())
-	 (symbol-qnames (eq (car-safe xml-ns) 'symbol-qnames))
-	 (xml-ns (if symbol-qnames (cdr xml-ns) xml-ns))
-	 end-pos name)
+  (let ((attlist ())
+        end-pos name)
     (skip-syntax-forward " ")
     (while (looking-at (eval-when-compile
 			 (concat "\\(" xml-name-re "\\)\\s-*=\\s-*")))

test/lisp/xml-tests.el

@@ -149,6 +149,21 @@ Parser is called with and without 'symbol-qnames argument.")
     (should (equal (cdr xml-parse-test--default-namespace-qnames)
                    (xml-parse-region nil nil nil nil 'symbol-qnames)))))
 
+;; Test bug #26533 (proper expansion in prefixed attributes with 'symbol-qnames)
+(defvar xml-parse-test--namespace-attribute-qnames
+  (cons "<something xmlns:a=\"myns:\"><whatever a:b='c'></whatever></something>"
+        '((something
+           ((("http://www.w3.org/2000/xmlns/" . "a")
+             . "myns:"))
+           (whatever
+            ((myns:b . "c")))))))
+
+(ert-deftest xml-parse-namespace-attribute-qnames ()
+  (with-temp-buffer
+    (insert (car xml-parse-test--namespace-attribute-qnames))
+    (should (equal (cdr xml-parse-test--namespace-attribute-qnames)
+                   (xml-parse-region nil nil nil nil 'symbol-qnames)))))
+
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