Rework tree generation mode and API

Store tree nodes in congruent, compact arena array.
Define handle types to refer to tree nodes rather than pointers to
structure instances.
Free tree with context.

assets/parser.h.erb

@@ -8,6 +8,9 @@
 
 #include <stdint.h>
 #include <stddef.h>
+<% if @cpp %>
+#include <vector>
+<% end %>
 
 /**************************************************************************
  * Public types
@@ -88,47 +91,29 @@ static inline <%= typestring %> <%= @grammar.prefix %>value_get<%= name == "defa
 <% end %>
 
 <% if @grammar.tree %>
-/** Tree node types. @{ */
-typedef struct <%= @grammar.tree_prefix %>Token<%= @grammar.tree_suffix %>
+/** Tree node ID type (index into the context node arena). ID 0 is null. */
+typedef uint32_t <%= @grammar.prefix %>node_id_t;
+
+/**
+ * Tree node record.
+ *
+ * All tree nodes are stored contiguously in the context node arena. Child
+ * links are stored in a shared children array: a node's children
+ * occupy children[child_offset .. child_offset + n_fields]. Token payload
+ * fields (token, pvalue, and any user fields) are only meaningful when
+ * is_token is nonzero.
+ */
+typedef struct
 {
-    <% # TreeNode fields must be present in the same order here. # %>
     <%= @grammar.prefix %>position_t position;
     <%= @grammar.prefix %>position_t end_position;
+    <%= @grammar.prefix %>node_id_t child_offset;
     uint16_t n_fields;
     uint8_t is_token;
-<%= @grammar.token_user_fields %>
     <%= @grammar.prefix %>token_t token;
     <%= @grammar.prefix %>value_t pvalue;
-} <%= @grammar.tree_prefix %>Token<%= @grammar.tree_suffix %>;
-
-<%   @parser.rule_sets.each do |name, rule_set| %>
-<%     next if name.start_with?("$") %>
-<%     next if rule_set.optional? %>
-struct <%= @grammar.tree_prefix %><%= name %><%= @grammar.tree_suffix %>;
-<%   end %>
-
-<%   @parser.rule_sets.each do |name, rule_set| %>
-<%     next if name.start_with?("$") %>
-<%     next if rule_set.optional? %>
-typedef struct <%= @grammar.tree_prefix %><%= name %><%= @grammar.tree_suffix %>
-{
-    <% # TreeNode 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.tree_fields.each do |fields| %>
-    union
-    {
-<%       fields.each do |field_name, type| %>
-        struct <%= type %> * <%= field_name %>;
-<%       end %>
-    };
-<%     end %>
-} <%= @grammar.tree_prefix %><%= name %><%= @grammar.tree_suffix %>;
-
-<%   end %>
-/** @} */
+<%= @grammar.token_user_fields %>
+} <%= @grammar.prefix %>node_data_t;
 <% end %>
 
 /** Lexed token information. */
@@ -179,7 +164,25 @@ typedef struct
 
     /** Parse result value. */
 <% if @grammar.tree %>
-    void * parse_result;
+    <%= @grammar.prefix %>node_id_t parse_result;
+
+<%   if @cpp %>
+    /** Tree node arena. Node ID 0 is reserved as the null node. */
+    std::vector<<%= @grammar.prefix %>node_data_t> <%= @grammar.prefix %>tree_nodes;
+
+    /** Shared tree child links. */
+    std::vector<<%= @grammar.prefix %>node_id_t> <%= @grammar.prefix %>tree_children;
+<%   else %>
+    /** Tree node arena. Node ID 0 is reserved as the null node. */
+    <%= @grammar.prefix %>node_data_t * <%= @grammar.prefix %>tree_nodes;
+    size_t <%= @grammar.prefix %>tree_nodes_length;
+    size_t <%= @grammar.prefix %>tree_nodes_capacity;
+
+    /** Shared tree child links. */
+    <%= @grammar.prefix %>node_id_t * <%= @grammar.prefix %>tree_children;
+    size_t <%= @grammar.prefix %>tree_children_length;
+    size_t <%= @grammar.prefix %>tree_children_capacity;
+<%   end %>
 <% else %>
     <%= @grammar.prefix %>value_t parse_result;
 <% end %>
@@ -193,6 +196,10 @@ typedef struct
 <%= @grammar.context_user_fields %>
 } <%= @grammar.prefix %>context_t;
 
+<% if @grammar.tree %>
+<%= c_tree_types_header %>
+<% end %>
+
 /**************************************************************************
  * Public data
  *************************************************************************/
@@ -217,9 +224,9 @@ size_t <%= @grammar.prefix %>parse_inner_<%= start_rule %>(<%= @grammar.prefix %
 <%   end %>
 
 <% if @grammar.tree %>
-<%= @grammar.tree_prefix %><%= @grammar.start_rules[0] %><%= @grammar.tree_suffix %> * <%= @grammar.prefix %>result(<%= @grammar.prefix %>context_t * context);
+<%= h_type(@grammar.start_rules[0]) %> <%= @grammar.prefix %>result(<%= @grammar.prefix %>context_t * context);
 <%   @grammar.start_rules.each_with_index do |start_rule, i| %>
-<%= @grammar.tree_prefix %><%= start_rule %><%= @grammar.tree_suffix %> * <%= @grammar.prefix %>result_<%= start_rule %>(<%= @grammar.prefix %>context_t * context);
+<%= h_type(start_rule) %> <%= @grammar.prefix %>result_<%= start_rule %>(<%= @grammar.prefix %>context_t * context);
 <%   end %>
 <% else %>
 <%= start_rule_type[1] %> <%= @grammar.prefix %>result(<%= @grammar.prefix %>context_t * context);
@@ -228,13 +235,6 @@ size_t <%= @grammar.prefix %>parse_inner_<%= start_rule %>(<%= @grammar.prefix %
 <%   end %>
 <% end %>
 
-<% if @grammar.tree %>
-void <%= @grammar.prefix %>tree_delete(<%= @grammar.tree_prefix %><%= @grammar.start_rules[0] %><%= @grammar.tree_suffix %> * tree);
-<%   @grammar.start_rules.each_with_index do |start_rule, i| %>
-void <%= @grammar.prefix %>tree_delete_<%= start_rule %>(<%= @grammar.tree_prefix %><%= start_rule %><%= @grammar.tree_suffix %> * tree);
-<%   end %>
-<% end %>
-
 <%= @grammar.prefix %>position_t <%= @grammar.prefix %>position(<%= @grammar.prefix %>context_t * context);
 
 void <%= @grammar.prefix %>set_position(<%= @grammar.prefix %>context_t * context, <%= @grammar.prefix %>position_t position);