Give rules::Visitor a virtual destructor

examples/grammars/helpers.cc

@@ -2,38 +2,38 @@
 
 namespace tree_sitter_examples {
     using namespace tree_sitter::rules;
-    
+
     rule_ptr comma_sep1(rule_ptr element) {
         return seq({ element, repeat(seq({ str(","), element })) });
     }
-    
+
     rule_ptr comma_sep(rule_ptr element) {
         return choice({ comma_sep1(element), blank() });
     }
-    
+
     rule_ptr optional(rule_ptr rule) {
         return choice({ rule, blank() });
     }
-    
+
     rule_ptr in_parens(rule_ptr rule) {
         return seq({ str("("), rule, str(")") });
     }
-    
+
     rule_ptr in_braces(rule_ptr rule) {
         return seq({ str("{"), rule, str("}") });
     }
-    
+
     rule_ptr in_brackets(rule_ptr rule) {
         return seq({ str("["), rule, str("]") });
     }
-    
+
     rule_ptr infix(int precedence, std::string op) {
         return prec(precedence, seq({
             sym("expression"),
             str(op),
             sym("expression") }));
     }
-    
+
     rule_ptr prefix(int precedence, std::string op) {
         return prec(precedence, seq({
             str(op),

examples/grammars/helpers.h

@@ -5,7 +5,7 @@
 
 namespace tree_sitter_examples {
     using namespace tree_sitter::rules;
-    
+
     rule_ptr comma_sep1(rule_ptr element);
     rule_ptr comma_sep(rule_ptr element);
     rule_ptr optional(rule_ptr rule);

src/compiler/rules/visitor.cc

@@ -12,8 +12,10 @@
 
 namespace tree_sitter {
     using std::vector;
-    
+
     namespace rules {
+        Visitor::~Visitor() {}
+
         rule_ptr IdentityRuleFn::default_apply(const Rule *rule) {
             return rule->copy();
         }

src/compiler/rules/visitor.h

@@ -28,6 +28,7 @@ namespace tree_sitter {
             virtual void visit(const String *rule) = 0;
             virtual void visit(const Symbol *rule) = 0;
             virtual void visit(const ISymbol *rule) = 0;
+            virtual ~Visitor();
         };
 
         template<typename T>