format

        pub fn format(self: DIFlags, w: *Writer) Writer.Error!void {
            var need_pipe = false;
            const info = @typeInfo(DIFlags).@"struct";
            inline for (info.field_names, info.field_types) |field_name, field_type| {
                switch (@typeInfo(field_type)) {
                    .bool => if (@field(self, field_name)) {
                        if (need_pipe) try w.writeAll(" | ") else need_pipe = true;
                        try w.print("DIFlag{s}", .{field_name});
                    },
                    .@"enum" => if (@field(self, field_name) != .Zero) {
                        if (need_pipe) try w.writeAll(" | ") else need_pipe = true;
                        try w.print("DIFlag{s}", .{@tagName(@field(self, field_name))});
                    },
                    .int => assert(@field(self, field_name) == 0),
                    else => @compileError("bad field type: " ++ field_name ++ ": " ++
                        @typeName(field_type)),
                }
            }
            if (!need_pipe) try w.writeByte('0');
        }