[PATCH v3 2/3] ox-texinfo: Optionally use @itemx for certain description list items

[Jonas Bernoulli <jonas@bernoul.li>]

* doc/org-manual.org (Plain lists in Texinfo export): Reorder and
document new functionality.
* lisp/ox-texinfo.el: Add org-texinfo--combine-items to the list of
:filter-parse-tree functions of the texinfo backend.
* lisp/ox-texinfo.el (org-texinfo--combine-items) New function.
* lisp/ox-texinfo.el (org-texinfo-item) Transcode combined items to
one @item and one or more @itemx.
---
 doc/org-manual.org | 38 +++++++++++++++++++++++++-----------
 lisp/ox-texinfo.el | 48 ++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 71 insertions(+), 15 deletions(-)

diff --git a/doc/org-manual.org b/doc/org-manual.org
index a5aac7d61..b3c4a9bef 100644
--- a/doc/org-manual.org
+++ b/doc/org-manual.org
@@ -15236,6 +15236,23 @@ This paragraph is preceded by...
 :DESCRIPTION: List attributes.
 :END:
 
+#+cindex: lettered lists, in Texinfo export
+#+cindex: enum, Texinfo attribute
+The Texinfo export back-end converts unordered and ordered lists in
+the Org file using the default command =@itemize=.
+
+Ordered lists are numbered when exported to Texinfo format.  Such
+numbering obeys any counter (see [[*Plain Lists]]) in the first item of
+the list.  The =:enum= attribute also let you start the list at a
+specific number, or switch to a lettered list, as illustrated here:
+
+#+begin_example
+#+ATTR_TEXINFO: :enum A
+1. Alpha
+2. Bravo
+3. Charlie
+#+end_example
+
 #+cindex: @samp{ATTR_TEXINFO}, keyword
 #+cindex: two-column tables, in Texinfo export
 #+cindex: table-type, Texinfo attribute
@@ -15262,7 +15279,7 @@ entry in the first column of the table.
 The following example illustrates all the attributes above:
 
 #+begin_example
-,#+ATTR_TEXINFO: :table-type vtable :sep , :indic asis
+,#+attr_texinfo: :table-type vtable :indic asis :sep ,
 - foo, bar :: This is the common text for variables foo and bar.
 #+end_example
 
@@ -15277,18 +15294,17 @@ This is the common text for variables foo and bar.
 @end table
 #+end_example
 
-#+cindex: lettered lists, in Texinfo export
-#+cindex: enum, Texinfo attribute
-Ordered lists are numbered when exported to Texinfo format.  Such
-numbering obeys any counter (see [[*Plain Lists]]) in the first item of
-the list.  The =:enum= attribute also let you start the list at
-a specific number, or switch to a lettered list, as illustrated here
+The =:combine= attribute is an alternative to the =:sep= attribute,
+which allows writing each entry on its own line.  If this attribute is
+non-nil and an item in a description list has no body but is followed
+by another item, then the second item is transcoded to =@itemx=.  This
+example is transcoded to the same output as above.
 
 #+begin_example
-#+ATTR_TEXINFO: :enum A
-1. Alpha
-2. Bravo
-3. Charlie
+,#+attr_texinfo: :table-type vtable :indic asis :combine t
+- foo ::
+- bar ::
+  This is the common text for variables foo and bar.
 #+end_example
 
 *** Tables in Texinfo export
diff --git a/lisp/ox-texinfo.el b/lisp/ox-texinfo.el
index 57cbcf6ad..36e1436d7 100644
--- a/lisp/ox-texinfo.el
+++ b/lisp/ox-texinfo.el
@@ -83,7 +83,8 @@ (org-export-define-backend 'texinfo
     (verse-block . org-texinfo-verse-block))
   :filters-alist
   '((:filter-headline . org-texinfo--filter-section-blank-lines)
-    (:filter-parse-tree . org-texinfo--normalize-headlines)
+    (:filter-parse-tree . (org-texinfo--normalize-headlines
+			   org-texinfo--combine-items))
     (:filter-section . org-texinfo--filter-section-blank-lines)
     (:filter-final-output . org-texinfo--untabify))
   :menu-entry
@@ -421,7 +422,7 @@ (defun org-texinfo--filter-section-blank-lines (headline _backend _info)
 (defun org-texinfo--normalize-headlines (tree _backend info)
   "Normalize headlines in TREE.
 
-BACK-END is the symbol specifying back-end used for export.
+_BACKEND is the symbol `texinfo'; the back-end used for export.
 INFO is a plist used as a communication channel.
 
 Make sure every headline in TREE contains a section, since those
@@ -443,6 +444,40 @@ (defun org-texinfo--normalize-headlines (tree _backend info)
     info)
   tree)
 
+(defun org-texinfo--combine-items (tree _backend info)
+  "Combine certain description list items.
+
+_BACKEND is the symbol `texinfo'; the back-end used for export.
+INFO is a plist used as a communication channel.
+
+If the `:combine' attribute of a description list is non-nil and
+an item in that list has no body and is followed by another item,
+then remove the first item and prepend its `:tag' to that of the
+second item.
+
+Such an item that absorbed the tags of other items is later
+transcoded to one `@item', followed by one or more `@itemx'.
+
+Return new tree."
+  (org-element-map tree 'item
+    (lambda (item)
+      (let ((plain-list (org-element-property :parent item)))
+	(when (and (org-not-nil (org-export-read-attribute
+				 :attr_texinfo plain-list :compact))
+		   (eq (org-element-property :type plain-list) 'descriptive))
+	  (let ((next-item
+		 (cadr (memq item (org-element-contents plain-list)))))
+	    (when (and next-item
+		       (not (org-element-contents item))
+		       (= (org-element-property :post-blank item) 1))
+	      (org-element-put-property
+	       next-item :itemx
+	       (nconc (org-element-property :itemx item)
+		      (list (org-element-property :tag item))))
+	      (org-element-extract-element item))))))
+    info)
+  tree)
+
 (defun org-texinfo--find-verb-separator (s)
   "Return a character not used in string S.
 This is used to choose a separator for constructs like \\verb."
@@ -994,8 +1029,13 @@ (defun org-texinfo-item (item contents info)
 		 (org-export-read-attribute :attr_texinfo
 					    (org-element-property :parent item)
 					    :sep)))
-	 (items (and tag
-		     (let ((tag (org-export-data tag info)))
+	 (items (org-element-property :itemx item))
+	 (items (cond (items
+		       (mapcar (lambda (tag) (org-export-data tag info))
+			       (nconc items (list tag))))
+		      ((not tag) nil)
+		      (t
+		       (setq tag (org-export-data tag info))
 		       (if split
 			   (split-string tag (regexp-quote split) t "[ \t\n]+")
 			 (list tag))))))
-- 
2.34.1