ast, cgen: fix generic method str() overload (#12330)

vlib/v/ast/types.v

@@ -1186,6 +1186,11 @@ pub fn (t &TypeSymbol) has_method(name string) bool {
 	return true
 }
 
+pub fn (t &TypeSymbol) has_method_with_generic_parent(name string) bool {
+	t.find_method_with_generic_parent(name) or { return false }
+	return true
+}
+
 pub fn (t &TypeSymbol) find_method(name string) ?Fn {
 	for method in t.methods {
 		if method.name == name {
@@ -1240,7 +1245,7 @@ pub fn (t &TypeSymbol) str_method_info() (bool, bool, int) {
 	mut has_str_method := false
 	mut expects_ptr := false
 	mut nr_args := 0
-	if sym_str_method := t.find_method('str') {
+	if sym_str_method := t.find_method_with_generic_parent('str') {
 		has_str_method = true
 		nr_args = sym_str_method.params.len
 		if nr_args > 0 {

vlib/v/gen/c/auto_str_methods.v

@@ -144,6 +144,9 @@ fn (mut g Gen) get_str_fn(typ ast.Type) string {
 			str_fn_name = styp_to_str_fn_name(sym.name)
 		}
 	}
+	if sym.has_method_with_generic_parent('str') && mut sym.info is ast.Struct {
+		str_fn_name = g.generic_fn_name(sym.info.concrete_types, str_fn_name, false)
+	}
 	g.str_types << StrType{
 		typ: unwrapped
 		styp: styp
@@ -157,7 +160,7 @@ fn (mut g Gen) final_gen_str(typ StrType) {
 	}
 	g.generated_str_fns << typ
 	sym := g.table.get_type_symbol(typ.typ)
-	if sym.has_method('str') && !typ.typ.has_flag(.optional) {
+	if sym.has_method_with_generic_parent('str') && !typ.typ.has_flag(.optional) {
 		return
 	}
 	styp := typ.styp

vlib/v/tests/generics_method_str_overload_test.v

@@ -0,0 +1,15 @@
+struct Gen<G> {
+	data G
+	id   int
+	size int
+}
+
+fn (g Gen<G>) str() string {
+	return 'Gen<G> $g.id, $g.data, ${g.size}.'
+}
+
+fn test_generics_method_str_overload() {
+	mut g := Gen<string>{'Gen', 0, 10}
+	println(g)
+	assert '$g' == 'Gen<G> 0, Gen, 10.'
+}