markused: fix markused auto str detection (fix #23501) (#23503)

Author: felipensp

vlib/v/checker/used_features.v

@@ -125,7 +125,9 @@ fn (mut c Checker) markused_call_expr(mut node ast.CallExpr) {
 
 fn (mut c Checker) markused_fn_call(mut node ast.CallExpr) {
 	if !c.is_builtin_mod && c.mod != 'math.bits' && node.args[0].expr !is ast.StringLiteral {
-		if !c.table.sym(c.unwrap_generic(node.args[0].typ)).has_method('str') {
+		if (node.args[0].expr is ast.CallExpr && node.args[0].expr.is_method
+			&& node.args[0].expr.name == 'str')
+			|| !c.table.sym(c.unwrap_generic(node.args[0].typ)).has_method('str') {
 			c.table.used_features.auto_str = true
 		} else {
 			if node.args[0].typ.has_option_or_result() {

vlib/v/tests/skip_unused/auto_str.run.out

@@ -0,0 +1,3 @@
+&TreeTwo{
+    Tree: 
+}

vlib/v/tests/skip_unused/auto_str.skip_unused.run.out

@@ -0,0 +1,3 @@
+&TreeTwo{
+    Tree: 
+}

vlib/v/tests/skip_unused/auto_str.vv

@@ -0,0 +1,20 @@
+module main
+
+pub struct Tree {}
+
+pub fn (tree &Tree) str() string {
+	return ''
+}
+
+pub struct TreeTwo {
+	Tree
+}
+
+pub fn TreeTwo.from_string(tree_string string) !&TreeTwo {
+	return &TreeTwo{}
+}
+
+fn main() {
+	tree := TreeTwo.from_string('') or { panic(err) }
+	println(tree.str())
+}