checker: fix missing check for empty array to generic param (fix #25056) (#25118)

Author: felipensp

vlib/v/checker/fn.v

@@ -1543,8 +1543,11 @@ fn (mut c Checker) fn_call(mut node ast.CallExpr, mut continue_check &bool) ast.
 			}
 		}
 		arg_typ_sym := c.table.sym(arg_typ)
-		if arg_typ_sym.kind == .none && param.typ.has_flag(.generic) && !param.typ.has_flag(.option) {
-			c.error('cannot use `none` as generic argument', call_arg.pos)
+		if param.typ.has_flag(.generic) {
+			if arg_typ_sym.kind == .none && !param.typ.has_flag(.option) {
+				c.error('cannot use `none` as generic argument', call_arg.pos)
+			}
+			c.check_unresolved_generic_param(node, call_arg)
 		}
 		param_typ_sym := c.table.sym(param.typ)
 		if func.is_variadic && arg_typ.has_flag(.variadic) && args_len - 1 > i {
@@ -2573,6 +2576,7 @@ fn (mut c Checker) method_call(mut node ast.CallExpr, mut continue_check &bool)
 			}
 		}
 		if exp_arg_typ.has_flag(.generic) {
+			c.check_unresolved_generic_param(node, arg)
 			method_concrete_types := if method_generic_names_len == rec_concrete_types.len {
 				rec_concrete_types
 			} else {
@@ -2753,6 +2757,13 @@ fn (mut c Checker) handle_generic_lambda_arg(node &ast.CallExpr, mut lambda ast.
 	}
 }
 
+fn (mut c Checker) check_unresolved_generic_param(node &ast.CallExpr, arg ast.CallArg) {
+	if node.raw_concrete_types.len == 0 && arg.expr is ast.ArrayInit
+		&& arg.expr.typ == ast.void_type {
+		c.error('cannot use empty array as generic argument', arg.pos)
+	}
+}
+
 fn (mut c Checker) spawn_expr(mut node ast.SpawnExpr) ast.Type {
 	ret_type := c.call_expr(mut node.call_expr)
 	if node.call_expr.or_block.kind != .absent {

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([])
+}