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

Util from the nvim-treesitter project.

src/nvim/lua/treesitter.c

@@ -90,6 +90,7 @@ static struct luaL_Reg node_meta[] = {
   { "prev_named_sibling", node_prev_named_sibling },
   { "named_children", node_named_children },
   { "root", node_root },
+  { "byte_length", node_byte_length },
 
   { NULL, NULL }
 };
@@ -1111,6 +1112,20 @@ static int node_root(lua_State *L)
   return 1;
 }
 
+static int node_byte_length(lua_State *L)
+{
+  TSNode node;
+  if (!node_check(L, 1, &node)) {
+    return 0;
+  }
+
+  uint32_t start_byte = ts_node_start_byte(node);
+  uint32_t end_byte = ts_node_end_byte(node);
+
+  lua_pushnumber(L, end_byte - start_byte);
+  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

@@ -92,4 +92,20 @@ describe('treesitter node API', function()
 
     eq(lua_eval('tostring(root)'), lua_eval('tostring(node:root())'))
   end)
+
+  it('can compute the byte length of a node', function()
+    insert([[
+      int main() {
+        int x = 3;
+      }]])
+
+    exec_lua([[
+      tree = vim.treesitter.get_parser(0, "c"):parse()[1]
+      root = tree:root()
+      child = root:child(0):child(0)
+    ]])
+
+    eq(28, lua_eval('root:byte_length()'))
+    eq(3, lua_eval('child:byte_length()'))
+  end)
 end)