XML sexp parsing doesn't correctly handle empty elements

[Bob131]

Expected behavior

Given a buffer with the following contents (where | indicates the point)

<tag>
  <tag/>
  |
</tag>

Executing M-: (sp-get-enclosing-sexp) RET should return (:beg 1 :end 25 :op "<tag>" :cl "</tag>" :prefix "" :suffix "").

Actual behavior

It returns (:beg 9 :end 25 :op "<tag/>" :cl "</tag>" :prefix "" :suffix "").

Environment & version information

• smartparens version: 37f77bf2e2199be9fe27e981317b02cfd0e8c70e
• Active major-mode: nxml-mode
• Emacs version (M-x emacs-version): 27.2
• Spacemacs/Evil/Other starterkit (specify which)/Vanilla: Evil
• OS: Fedora

[Bob131]

I dug into this a bit, and it seems like the issue is partly the search loop in sp-get-sgml-tag and partly that sp--sgml-opening-p is not quite correct. This rough diff fixes the issue:

diff --git a/smartparens.el b/smartparens.el
index fd58064..2000ef6 100644
--- a/smartparens.el
+++ b/smartparens.el
@@ -5409,6 +5409,19 @@ and newline."
 (defun sp--sgml-opening-p (tag)
   (not (equal "/" (substring tag 1 2))))

+(defun sp--looking-at-sgml-opening-p ()
+  (let ((sexp (sp-get-paired-expression)))
+    (and sexp
+         (equal (plist-get sexp :op) "<")
+         (equal (plist-get sexp :cl) ">")
+         (not (= (char-after (1+ (plist-get sexp :beg)))
+                 ?/))
+         (not (= (char-before (1- (plist-get sexp :end)))
+                 ?/)))))
+
+(defun sp--looking-at-sgml-closing-p ()
+  (looking-at-p "</"))
+
 (defun sp--sgml-ignore-tag (tag)
   "Return non-nil if tag should be ignored in search, nil otherwise."
   (member tag '("!--" "!DOCTYPE")))
@@ -5446,9 +5459,11 @@ and newline."
               (goto-char (match-end 0))))
             (while (> depth 0)
               (if (funcall search-fn needle nil t)
-                  (if (sp--sgml-opening-p (match-string 0))
-                      (if forward (setq depth (1+ depth)) (setq depth (1- depth)))
-                    (if forward (setq depth (1- depth)) (setq depth (1+ depth))))
+                  (cond
+                   ((sp--looking-at-sgml-opening-p)
+                    (if forward (setq depth (1+ depth)) (setq depth (1- depth))))
+                   ((sp--looking-at-sgml-closing-p)
+                    (if forward (setq depth (1- depth)) (setq depth (1+ depth)))))
                 (setq depth -1)))
             (if (eq depth -1)
                 (progn (sp-message :no-matching-tag) nil)

[Bob131]

Hmm, that doesn't work in the case that the initial match at https://github.com/Fuco1/smartparens/blob/37f77bf2e2199be9fe27e981317b02cfd0e8c70e/smartparens.el#L5424 is an empty element. I guess sp-get-sgml-tag needs to be changed to test when the point is inside an empty element first, and if not search forward for a tag that isn't an empty element.