Move reusable node functions to their own file

src/runtime/reusable_node.h

@@ -0,0 +1,50 @@
+#include "runtime/tree.h"
+
+typedef struct {
+  Tree *tree;
+  uint32_t byte_index;
+  bool has_preceding_external_token;
+  const TSExternalTokenState *preceding_external_token_state;
+} ReusableNode;
+
+static inline ReusableNode reusable_node_new(Tree *tree) {
+  return (ReusableNode){
+    .tree = tree,
+    .byte_index = 0,
+    .has_preceding_external_token = false,
+    .preceding_external_token_state = NULL,
+  };
+}
+
+static inline void reusable_node_pop(ReusableNode *self) {
+  self->byte_index += ts_tree_total_bytes(self->tree);
+  if (self->tree->has_external_tokens) {
+    self->has_preceding_external_token = true;
+    self->preceding_external_token_state = ts_tree_last_external_token_state(self->tree);
+  }
+
+  while (self->tree) {
+    Tree *parent = self->tree->context.parent;
+    uint32_t next_index = self->tree->context.index + 1;
+    if (parent && parent->child_count > next_index) {
+      self->tree = parent->children[next_index];
+      return;
+    }
+    self->tree = parent;
+  }
+}
+
+static inline void reusable_node_pop_leaf(ReusableNode *self) {
+  while (self->tree->child_count > 0)
+    self->tree = self->tree->children[0];
+  reusable_node_pop(self);
+}
+
+static inline bool reusable_node_breakdown(ReusableNode *self) {
+  if (self->tree->child_count == 0) {
+    return false;
+  } else {
+    self->tree = self->tree->children[0];
+    return true;
+  }
+}