fix

vlib/v/checker/fn.v

@@ -2576,6 +2576,9 @@ fn (mut c Checker) method_call(mut node ast.CallExpr, mut continue_check &bool)
 			}
 		}
 		if exp_arg_typ.has_flag(.generic) {
+			if arg.expr is ast.ArrayInit && arg.expr.exprs.len == 0 {
+				c.error('cannot use empty array as generic argument', arg.pos)
+			}
 			method_concrete_types := if method_generic_names_len == rec_concrete_types.len {
 				rec_concrete_types
 			} else {

vlib/v/checker/tests/empty_arr_to_generic_param_err.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/empty_arr_to_generic_param_err.vv:8:4: error: cannot use empty array as generic argument
+    6 | 
+    7 | fn main() {
+    8 |     t([])
+      |       ~~
+    9 |     Foo{}.t([])
+   10 | }
+vlib/v/checker/tests/empty_arr_to_generic_param_err.vv:9:10: error: cannot use empty array as generic argument
+    7 | fn main() {
+    8 |     t([])
+    9 |     Foo{}.t([])
+      |             ~~
+   10 | }

vlib/v/checker/tests/empty_arr_to_generic_param_err.vv

@@ -0,0 +1,10 @@
+fn t[T](a []T) {}
+
+struct Foo {}
+
+fn (t &Foo) t[T](a []T) {}
+
+fn main() {
+	t([])
+	Foo{}.t([])
+}