union #no_nil

core/fmt/fmt.odin

@@ -1326,8 +1326,14 @@ fmt_value :: proc(fi: ^Info, v: any, verb: rune) {
 		case i64:  tag = i64(i);
 		case: panic("Invalid union tag type");
 		}
+		assert(tag >= 0);
 
-		if v.data == nil || tag == 0 {
+		if v.data == nil {
+			strings.write_string(fi.buf, "nil");
+		} else if info.no_nil {
+			id := info.variants[tag].id;
+			fmt_arg(fi, any{v.data, id}, verb);
+		} else if tag == 0 {
 			strings.write_string(fi.buf, "nil");
 		} else {
 			id := info.variants[tag-1].id;

core/runtime/core.odin

@@ -86,10 +86,11 @@ Type_Info_Struct :: struct {
 	custom_align: bool,
 };
 Type_Info_Union :: struct {
-	variants:   []^Type_Info,
-	tag_offset: uintptr,
-	tag_type:   ^Type_Info,
+	variants:     []^Type_Info,
+	tag_offset:   uintptr,
+	tag_type:     ^Type_Info,
 	custom_align: bool,
+	no_nil:       bool,
 };
 Type_Info_Enum :: struct {
 	base:      ^Type_Info,