ox-texinfo: Fix edge case with - Variable: nil:: definition

* lisp/ox-texinfo.el (org-texinfo--split-definition): Do not store
definition options as :attr_texinfo read by
`org-export-read-attribute'.  `org-export-read-attribute' is incapable
of reading literal nil.  Instead, store the options literally, as is,
in a special non-standard syntax node property.
(org-texinfo-special-block): Make use of syntax node property used by
`org-texinfo--split-definition', when present.
* testing/lisp/test-ox-texinfo.el (test-ox-texinfo/definition): New
test.

Reported-by: 8dcc <8dcc.git@gmail.com>
Link: https://orgmode.org/list/87plo98a8g.fsf@gmail.com

lisp/ox-texinfo.el

@@ -680,7 +680,11 @@ specified by CMD and ARGS."
     (org-element-insert-before
      (apply #'org-element-create 'special-block
 	    (list :type cmd
-		  :attr_texinfo (list (format ":options %s" args))
+                  :ox-texinfo--options args
+                  ;; Option can be nil that cannot be recorgnized
+                  ;; literally by `org-export-read-attribute', so we
+                  ;; use dedicated property instead
+		  ;; :attr_texinfo (list (format ":options %s" args))
 		  :post-blank (if contents 1 0))
 	    (mapc #'org-element-extract contents))
      plain-list))
@@ -1689,7 +1693,10 @@ holding contextual information."
   "Transcode a SPECIAL-BLOCK element from Org to Texinfo.
 CONTENTS holds the contents of the block.  INFO is a plist used
 as a communication channel."
-  (let ((opt (org-export-read-attribute :attr_texinfo special-block :options))
+  (let ((opt (or
+              ;; See `org-texinfo--split-definition'
+              (org-element-property :ox-texinfo--options special-block)
+              (org-export-read-attribute :attr_texinfo special-block :options)))
 	(type (org-element-property :type special-block)))
     (format "@%s%s\n%s@end %s"
 	    type

testing/lisp/test-ox-texinfo.el

@@ -403,5 +403,47 @@ body
           (re-search-forward
            "^@chapter Heading 2 (@ref{Heading 1, , Heading 1})$")))))))
 
+
+
+;;; Definitions
+
+(ert-deftest test-ox-texinfo/definition ()
+  "Test definitions."
+  (should
+   (org-test-with-temp-text
+       (string-join
+        (list "- Variable: name ::"
+              "  Description")
+        "\n")
+     (let ((export-buffer "*Test Texinfo Export*")
+           (org-export-show-temporary-export-buffer nil))
+       (org-export-to-buffer 'texinfo export-buffer
+         nil nil nil nil nil
+         #'texinfo-mode)
+       (with-current-buffer export-buffer
+         (goto-char (point-min))
+         (and
+          (re-search-forward "@defvar name")
+          (re-search-forward "Description")
+          (re-search-forward "@end defvar"))))))
+  ;; Edge case: Variable name = nil
+  (should
+   (org-test-with-temp-text
+       (string-join
+        (list "- Variable: nil ::"
+              "  Description")
+        "\n")
+     (let ((export-buffer "*Test Texinfo Export*")
+           (org-export-show-temporary-export-buffer nil))
+       (org-export-to-buffer 'texinfo export-buffer
+         nil nil nil nil nil
+         #'texinfo-mode)
+       (with-current-buffer export-buffer
+         (goto-char (point-min))
+         (and
+          (re-search-forward "@defvar nil")
+          (re-search-forward "Description")
+          (re-search-forward "@end defvar")))))))
+
 (provide 'test-ox-texinfo)
 ;;; test-ox-texinfo.el end here