checker: fix generics that return multi generics struct (#9852)

vlib/v/checker/checker.v

@@ -1434,9 +1434,18 @@ fn (mut c Checker) check_return_generics_struct(return_type ast.Type, mut call_e
 	rts := c.table.get_type_symbol(return_type)
 	if rts.info is ast.Struct {
 		if rts.info.generic_types.len > 0 {
-			gts := c.table.get_type_symbol(call_expr.generic_types[0])
-			nrt := '$rts.name<$gts.name>'
-			c_nrt := '${rts.name}_T_$gts.name'
+			mut nrt := '$rts.name<'
+			mut c_nrt := '${rts.name}_T_'
+			for i in 0 .. call_expr.generic_types.len {
+				gts := c.table.get_type_symbol(call_expr.generic_types[i])
+				nrt += gts.name
+				c_nrt += gts.name
+				if i != call_expr.generic_types.len - 1 {
+					nrt += ','
+					c_nrt += '_'
+				}
+			}
+			nrt += '>'
 			idx := c.table.type_idxs[nrt]
 			if idx != 0 {
 				c.ensure_type_exists(idx, call_expr.pos) or {}

vlib/v/tests/generics_return_multiple_generics_struct_test.v

@@ -0,0 +1,38 @@
+struct Foo<A, B> {
+mut:
+	a A
+	b B
+}
+
+fn new_foo<A, B>(a A, b B) Foo<A, B> {
+	return {
+		a: a
+		b: b
+	}
+}
+
+fn get_a<A, B>(opt Foo<A, B>) A {
+	return opt.a
+}
+
+fn get_b<A, B>(opt Foo<A, B>) B {
+	return opt.b
+}
+
+fn set<A, B>(mut opt Foo<A, B>, a A, b B) {
+	opt.a = a
+	opt.b = b
+}
+
+fn test_generics_return_multiple_generics_struct() {
+	mut o := new_foo<int, string>(23, 'aaa')
+	println(get_a<int, string>(o))
+	assert get_a<int, string>(o) == 23
+	println(get_b<int, string>(o))
+	assert get_b<int, string>(o) == 'aaa'
+	set<int, string>(mut o, 42, 'bbb')
+	println(get_a<int, string>(o))
+	assert get_a<int, string>(o) == 42
+	println(get_b<int, string>(o))
+	assert get_b<int, string>(o) == 'bbb'
+}