feat(ruby): Enhance Ruby parser (#26)

* feat(ruby): Add fold range for do_block node

* feat(ruby): support if, elsif, and else

Author: jcs090218

ts-fold-parsers.el

@@ -47,7 +47,8 @@
 (declare-function ts-fold-range-html "ts-fold.el")
 (declare-function ts-fold-range-ocaml "ts-fold.el")
 (declare-function ts-fold-range-python "ts-fold.el")
-(declare-function ts-fold-range-ruby "ts-fold.el")
+(declare-function ts-fold-range-ruby-class-def "ts-fold.el")
+(declare-function ts-fold-range-ruby-if "ts-fold.el")
 (declare-function ts-fold-range-rust-macro "ts-fold.el")
 (declare-function ts-fold-range-elixir "ts-fold.el")
 
@@ -194,9 +195,13 @@
 
 (defun ts-fold-parsers-ruby ()
   "Rule set for Ruby."
-  '((class  . ts-fold-range-ruby)
-    (method . ts-fold-range-ruby)
-    (array  . ts-fold-range-seq)
+  '((class    . ts-fold-range-ruby-class-def)
+    (method   . ts-fold-range-ruby-class-def)
+    (array    . ts-fold-range-seq)
+    (do       . (ts-fold-range-seq 1 -2))  ; match with `end`
+    (do_block . (ts-fold-range-seq 1 -2))  ; match with `end`, in spec file
+    (then     . ts-fold-range-ruby-if)        ; `if` and `elsif` block
+    (else     . (ts-fold-range-ruby-if 4 0))  ; `else` block
     (comment
      . (lambda (node offset)
          (ts-fold-range-line-comment node offset "#")))))

ts-fold.el

@@ -550,7 +550,7 @@ more information."
               (end (tsc-node-end-position node)))
     (ts-fold--cons-add (cons beg end) offset)))
 
-(defun ts-fold-range-ruby (node offset)
+(defun ts-fold-range-ruby-class-def (node offset)
   "Define fold range for `method' and `class' in Ruby.
 
 For arguments NODE and OFFSET, see function `ts-fold-range-seq' for
@@ -560,6 +560,15 @@ more information."
                               (tsc-get-child-by-field node :name)))
               (beg (tsc-node-end-position named-node))
               (end (tsc-node-end-position node)))
+    (ts-fold--cons-add (cons beg (- end 3)) offset)))
+
+(defun ts-fold-range-ruby-if (node offset)
+  "Define fold range for `if' (then), `elsif', and `else' in Ruby.
+
+For arguments NODE and OFFSET, see function `ts-fold-range-seq' for
+more information."
+  (when-let ((beg (tsc-node-start-position node))
+             (end (tsc-node-end-position node)))
     (ts-fold--cons-add (cons beg end) offset)))
 
 (defun ts-fold-range-rust-macro (node offset)