Pass reference to parser in stack's tree selection callback

spec/runtime/stack_spec.cc

@@ -43,7 +43,9 @@ describe("Stack", [&]() {
   TSSymbolMetadata metadata = {true, true, true};
 
   before_each([&]() {
-    stack = ts_stack_new({
+    stack = ts_stack_new();
+
+    ts_stack_set_tree_selection_callback(stack, {
       &tree_selection_spy,
       tree_selection_spy_callback
     });

src/runtime/parser.c

@@ -433,6 +433,9 @@ static void ts_parser__start(TSParser *self, TSInput input,
 
   ts_lexer_set_input(&self->lexer, input);
   ts_stack_clear(self->stack);
+  ts_stack_set_tree_selection_callback(self->stack, (TreeSelectionCallback){
+    self, ts_parser__select_tree,
+  });
 
   LookaheadState lookahead_state = {
     .reusable_subtree = previous_tree,
@@ -582,9 +585,7 @@ static ConsumeResult ts_parser__consume_lookahead(TSParser *self, int head,
 TSParser ts_parser_make() {
   return (TSParser){
     .lexer = ts_lexer_make(),
-    .stack = ts_stack_new((TreeSelectionCallback){
-      NULL, ts_parser__select_tree,
-    }),
+    .stack = ts_stack_new(),
     .lookahead_states = vector_new(sizeof(LookaheadState), 4),
     .reduce_parents = vector_new(sizeof(TSTree *), 4),
   };

src/runtime/stack.c

@@ -36,13 +36,17 @@ typedef struct {
  *  Section: Stack lifecycle
  */
 
-Stack *ts_stack_new(TreeSelectionCallback tree_selection_callback) {
+static TSTree *ts_stack__default_tree_selection(void *p, TSTree *t1, TSTree *t2) {
+  return t1;
+}
+
+Stack *ts_stack_new() {
   Stack *self = malloc(sizeof(Stack));
   *self = (Stack){
     .heads = calloc(INITIAL_HEAD_CAPACITY, sizeof(StackNode *)),
     .head_count = 1,
     .head_capacity = INITIAL_HEAD_CAPACITY,
-    .tree_selection_callback = tree_selection_callback,
+    .tree_selection_callback = {NULL, ts_stack__default_tree_selection},
     .pop_results = vector_new(sizeof(StackPopResult), 4),
     .pop_paths = vector_new(sizeof(PopPath), 4),
   };
@@ -351,3 +355,7 @@ void ts_stack_clear(Stack *self) {
   self->head_count = 1;
   self->heads[0] = NULL;
 }
+
+void ts_stack_set_tree_selection_callback(Stack *self, TreeSelectionCallback callback) {
+  self->tree_selection_callback = callback;
+}

src/runtime/stack.h

@@ -24,13 +24,13 @@ typedef struct {
 
 typedef struct {
   void *data;
-  TSTree *(*callback)(void *data, TSTree *, TSTree *);
+  TSTree *(*callback)(void *, TSTree *, TSTree *);
 } TreeSelectionCallback;
 
 /*
  *  Create a parse stack.
  */
-Stack *ts_stack_new(TreeSelectionCallback);
+Stack *ts_stack_new();
 
 /*
  *  Release any resources reserved by a parse stack.
@@ -117,6 +117,8 @@ void ts_stack_remove_head(Stack *, int head);
  */
 void ts_stack_clear(Stack *);
 
+void ts_stack_set_tree_selection_callback(Stack *, TreeSelectionCallback);
+
 #ifdef __cplusplus
 }
 #endif