Add p_free_ast() to free AST node memory for C targets

assets/parser.h.erb

@@ -75,9 +75,11 @@ typedef union
 /** AST node types. @{ */
 typedef struct <%= @grammar.ast_prefix %>Token<%= @grammar.ast_suffix %>
 {
-    /* ASTNode fields must be present in the same order here. */
+    <% # ASTNode fields must be present in the same order here. # %>
     <%= @grammar.prefix %>position_t position;
     <%= @grammar.prefix %>position_t end_position;
+    uint16_t n_fields;
+    uint8_t is_token;
     <%= @grammar.prefix %>token_t token;
     <%= @grammar.prefix %>value_t pvalue;
 } <%= @grammar.ast_prefix %>Token<%= @grammar.ast_suffix %>;
@@ -93,8 +95,11 @@ struct <%= name %>;
 <%     next if rule_set.optional? %>
 typedef struct <%= @grammar.ast_prefix %><%= name %><%= @grammar.ast_suffix %>
 {
+    <% # ASTNode fields must be present in the same order here. # %>
     <%= @grammar.prefix %>position_t position;
     <%= @grammar.prefix %>position_t end_position;
+    uint16_t n_fields;
+    uint8_t is_token;
 <%     rule_set.ast_fields.each do |fields| %>
     union
     {
@@ -187,6 +192,8 @@ size_t <%= @grammar.prefix %>parse(<%= @grammar.prefix %>context_t * context);
 
 <% if @grammar.ast %>
 <%= @grammar.ast_prefix %><%= @grammar.start_rule %><%= @grammar.ast_suffix %> * <%= @grammar.prefix %>result(<%= @grammar.prefix %>context_t * context);
+
+void <%= @grammar.prefix %>free_ast(<%= @grammar.ast_prefix %><%= @grammar.start_rule %><%= @grammar.ast_suffix %> * ast);
 <% else %>
 <%= start_rule_type[1] %> <%= @grammar.prefix %>result(<%= @grammar.prefix %>context_t * context);
 <% end %>