From 50dc88a56cc13030801bfefc7116828d4115ae70 Mon Sep 17 00:00:00 2001
From: keke <librek@protonmail.com>
Date: Wed, 2 Jun 2021 18:09:03 +0800
Subject: fix error: 'optional' in namespace 'std' does not name a template
 type

---
 src/libfetchers/attrs.hh | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/libfetchers/attrs.hh b/src/libfetchers/attrs.hh
index a2d53a7bf..e41037633 100644
--- a/src/libfetchers/attrs.hh
+++ b/src/libfetchers/attrs.hh
@@ -6,6 +6,8 @@
 
 #include <nlohmann/json_fwd.hpp>
 
+#include <optional>
+
 namespace nix::fetchers {
 
 typedef std::variant<std::string, uint64_t, Explicit<bool>> Attr;
-- 
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