feat(treesitter): upstream get_named_children() as a node method

Util from the nvim-treesitter project.

src/nvim/lua/treesitter.c

@@ -88,6 +88,7 @@ static struct luaL_Reg node_meta[] = {
   { "prev_sibling", node_prev_sibling },
   { "next_named_sibling", node_next_named_sibling },
   { "prev_named_sibling", node_prev_named_sibling },
+  { "named_children", node_named_children },
   { NULL, NULL }
 };
 
@@ -1062,6 +1063,31 @@ static int node_prev_named_sibling(lua_State *L)
   return 1;
 }
 
+static int node_named_children(lua_State *L)
+{
+  TSNode source;
+  if (!node_check(L, 1, &source)) {
+    return 0;
+  }
+  TSTreeCursor cursor = ts_tree_cursor_new(source);
+
+  lua_newtable(L);
+  int curr_index = 0;
+
+  if (ts_tree_cursor_goto_first_child(&cursor)) {
+    do {
+      TSNode node = ts_tree_cursor_current_node(&cursor);
+      if (ts_node_is_named(node)) {
+        push_node(L, node, 1);
+        lua_rawseti(L, -2, ++curr_index);
+      }
+    } while (ts_tree_cursor_goto_next_sibling(&cursor));
+  }
+
+  ts_tree_cursor_delete(&cursor);
+  return 1;
+}
+
 /// assumes the match table being on top of the stack
 static void set_match(lua_State *L, TSQueryMatch *match, int nodeidx)
 {

test/functional/treesitter/node_spec.lua

@@ -59,4 +59,22 @@ describe('treesitter node API', function()
     exec_lua 'node = node:prev_named_sibling()'
     eq('int x', lua_eval('node_text(node)'))
   end)
+
+  it('can retrieve the children of a node', function()
+    insert([[
+      int main() {
+        int x = 3;
+      }]])
+
+    local len = exec_lua([[
+      tree = vim.treesitter.get_parser(0, "c"):parse()[1]
+      node = tree:root():child(0)
+      children = node:named_children()
+
+      return #children
+    ]])
+
+    eq(3, len)
+    eq('<node compound_statement>', lua_eval('tostring(children[3])'))
+  end)
 end)