parse markdown headings (#13)

* parse markdown headings

* document next heading function

* replace treesit-node-get call with treesit-node-next-sibling

treesit-fold-parsers.el

@@ -72,6 +72,8 @@
 (declare-function treesit-fold-range-lua-do-loop "treesit-fold.el")
 (declare-function treesit-fold-range-lua-repeat "treesit-fold.el")
 (declare-function treesit-fold-range-make-recipe "treesit-fold.el")
+(declare-function treesit-fold-markdown-heading "treesit-fold.el")
+(declare-function treesit-fold-markdown-code-block "treesit-fold.el")
 (declare-function treesit-fold-range-matlab-function "treesit-fold.el")
 (declare-function treesit-fold-range-matlab-statements "treesit-fold.el")
 (declare-function treesit-fold-range-matlab-blocks "treesit-fold.el")
@@ -450,7 +452,8 @@
 
 (defun treesit-fold-parsers-markdown ()
   "Rule set for Markdown."
-  '((fenced_code_block . (treesit-fold-range-seq 2 -2))
+  '((fenced_code_block . treesit-fold-markdown-code-block)
+    (section . treesit-fold-markdown-heading)
     (html_block        . treesit-fold-range-html)))
 
 (defun treesit-fold-parsers-matlab ()

treesit-fold.el

@@ -1153,6 +1153,47 @@ more information."
               (end (treesit-node-end last-child)))
     (treesit-fold--cons-add (cons beg end) offset)))
 
+(defun treesit-fold-markdown-next-heading (node siblings)
+  "Return first heading from SIBLINGS with start point after NODE.
+If there is no sibling, then return nil."
+  (or
+   (seq-find
+    (lambda (n)
+      (when-let ((child (treesit-node-child n 0 t)))
+        (and (> (treesit-node-start child) (treesit-node-start node))
+             (treesit-fold--compare-type child "atx_heading"))))
+    (remove node siblings))
+   (treesit-node-next-sibling (treesit-node-parent node) t)))
+
+(defun treesit-fold-markdown-heading (node offset)
+  "Define fold range for Markdown headings.
+
+For arguments NODE and OFFSET, see function `treesit-fold-range-seq' for
+more information."
+  (when-let*
+      ((parent (treesit-node-parent node))
+       (head (treesit-node-child node 0 t))
+       (beg  (treesit-node-start node))
+       (siblings (treesit-fold-find-children parent "section"))
+       (end (1-
+             (or (treesit-node-start
+                  (treesit-fold-markdown-next-heading node siblings))
+                 (point-max))))
+       (name (length (string-trim (or (treesit-node-text head) "")))))
+    (treesit-fold--cons-add (cons beg end) (cons name 0))))
+
+(defun treesit-fold-markdown-code-block (node offset)
+  "Define fold range for Markdown code blocks.
+
+For arguments NODE and OFFSET, see function `treesit-fold-range-seq' for
+more information."
+  (let* ((beg (1+ (treesit-node-start node)))
+         (end (1- (treesit-node-end node)))
+         (name (+ 2 (length
+                     (or (treesit-node-text (treesit-node-child node 1))
+                         "")))))
+    (treesit-fold--cons-add (cons beg end) (cons name -2))))
+
 (defun treesit-fold-range-matlab-blocks (node offset)
   "Define fold range for MATLAB blocks.