Add extra folding definitions for golang

Author: samrjack

README.md

@@ -185,6 +185,30 @@ For the folding functions, ts-fold provides some default
   int main() {...} // Folded node
   ```
 
+- `ts-fold-range-markers` - Folds the node starting from a giving delimiter
+  character. Useful if tree-sitter's node definition doesn't align with the
+  start of the desired folding section.
+
+  **NOTE:** This folding function requires a lambda (or an externally
+  defined function wrapper) so that the delimiter can be specified. You
+  usually don't need to worry about the `node` and `offset` variables, so just
+  pass them through.
+
+```go
+type Dog interface {
+    Bark() (string, error)
+    Beg() (bool, error)
+}
+
+/* | Note: The tree-sitter node starts at the word interface, not at the '{'.
+ * | '(interface_type . (lambda (node offset)
+ * |                      (ts-fold-range-markers node offset "{" "}")))
+ * V
+ */
+
+type Dog interface {...}
+```
+
 - `ts-fold-range-block-comment` - Folds multi-line comments that are of the form
   `/*...*/`. Should show a summary if the commentary plugin is turned on.
 
@@ -210,8 +234,10 @@ For the folding functions, ts-fold provides some default
 
 - `ts-fold-range-line-comment` - For languages that have one line comment blocks
   with the comment delimiter starting each line. Condenses all the comment nodes
-  into a single fold. This folding function requires a lambda (or an externally
-  defined function wrapper) so that the comment delimiter can be specified. You
+  into a single fold.
+
+  **Note:** This folding function requires a lambda (or an externally
+  defined function wrapper) so that the delimiter can be specified. You
   usually don't need to worry about the `node` and `offset` variables, so just
   pass them through.
 

ts-fold-parsers.el

@@ -122,8 +122,14 @@
 
 (defun ts-fold-parsers-go ()
   "Rule set for Go."
-  '((block   . ts-fold-range-seq)
-    (comment . ts-fold-range-seq)))
+  '((block                  . ts-fold-range-seq)
+    (comment                . ts-fold-range-seq)
+    (const_declaration      . (lambda (node offset)
+                                (ts-fold-range-markers node offset "(" ")")))
+    (field_declaration_list . ts-fold-range-seq)
+    (import_spec_list       . ts-fold-range-seq)
+    (interface_type         . (lambda (node offset)
+                                (ts-fold-range-markers node offset "{" "}")))))
 
 (defun ts-fold-parsers-html ()
   "Rule set for HTML."

ts-fold.el

@@ -392,6 +392,27 @@ Argument OFFSET can be used to tweak the final beginning and end position."
         (end (1- (tsc-node-end-position node))))
     (ts-fold--cons-add (cons beg end) offset)))
 
+(defun ts-fold-range-markers (node offset start-seq &optional end-seq)
+  "Returns the fold range for NODE with an OFFSET where the range starts at
+the end of the first occurence of START-SEQ and ends at the end of the node
+or the last occurence of the optional parameter LAST-SEQ.
+
+
+If no occurence is found for START-SEQ or END-SEQ or the
+occurences overlap, then the range returned is nil."
+  (when start-seq
+    (let ((beg (tsc-node-start-position node))
+          (end (tsc-node-end-position node)))
+      (save-excursion
+        (when-let* ((start-position (progn (goto-char beg)
+                                           (search-forward start-seq end t)))
+                    (end-position (if end-seq
+                                      (progn (goto-char end)
+                                             (search-backward end-seq beg t))
+                                    (1- end))))
+          (unless (> start-position end-position)
+            (ts-fold--cons-add (cons start-position end-position) offset)))))))
+
 (defun ts-fold-range-line-comment (node offset prefix)
   "Define fold range for line comment.