c error while compiling using with the v ui libr... (fixes #18952)

Author: medvednikov

vlib/v/gen/c/fn.v

@@ -2392,20 +2392,14 @@ fn (mut g Gen) autofree_call_pregen(node ast.CallExpr) {
 			s = 'string ${t} = '
 		}
 		g.is_autofree_tmp = true
-		pos_before := g.out.len
-
 		old_is_autofree := g.is_autofree
 		if arg.expr is ast.CallExpr && arg.expr.is_method && arg.expr.left is ast.CallExpr {
 			g.is_autofree = false
 		}
 
-		g.expr(arg.expr)
-		expr_code := g.out.cut_to(pos_before).trim_space()
-
+		s = g.expr_string_surround(s, arg.expr, ';').trim_space()
 		g.is_autofree = old_is_autofree
 		g.is_autofree_tmp = false
-		s += expr_code
-		s += ';'
 		g.strs_to_free0 << s
 		// This tmp arg var will be freed with the rest of the vars at the end of the scope.
 	}

vlib/v/tests/autofree_if_expr_call_arg_with_struct_init_test.v

@@ -0,0 +1,28 @@
+// vtest vflags: -autofree
+module main
+
+const no_style = 'no_style'
+const no_string = ''
+
+struct TextStyleParams {
+	id             string = no_style
+	font_name      string = no_string
+	color          string
+	size           int = -1
+	align          int
+	vertical_align int
+}
+
+fn draw_text(text string, ts TextStyleParams) string {
+	return text + ts.color
+}
+
+fn test_autofree_if_expr_call_arg_with_struct_init() {
+	files_dropped := true
+	got := draw_text(if files_dropped {
+		'Empty listbox. Drop files here ...'
+	} else {
+		''
+	}, color: 'gray')
+	assert got == 'Empty listbox. Drop files here ...gray'
+}