checker: fix generic array clone (#17153)

Author: felipensp

vlib/v/checker/fn.v

@@ -2232,7 +2232,11 @@ fn (mut c Checker) array_builtin_method_call(mut node ast.CallExpr, left_type as
 	if method_name == 'slice' && !c.is_builtin_mod {
 		c.error('.slice() is a private method, use `x[start..end]` instead', node.pos)
 	}
-	array_info := left_sym.info as ast.Array
+	array_info := if left_sym.info is ast.Array {
+		left_sym.info as ast.Array
+	} else {
+		c.table.sym(c.unwrap_generic(left_type)).info as ast.Array
+	}
 	elem_typ = array_info.elem_type
 	if method_name in ['filter', 'map', 'any', 'all'] {
 		// position of `it` doesn't matter

vlib/v/tests/generic_array_clone_test.v

@@ -0,0 +1,8 @@
+fn test_main() {
+	encode([]int{len: 5, init: 5})
+}
+
+fn encode[U](val U) {
+	new_val := val.clone()
+	assert new_val == [5, 5, 5, 5, 5]
+}