fix(3p/tvix): properly zero the largest member of Value r/1793

The static_assert is present to force us to change the constructor when a member grows.

Change-Id: Ifa4f4a03eb7ce13cff109cf26ecf0032045905e9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1972
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

1 files changed, 4 insertions, 1 deletions

diff --git a/third_party/nix/src/libexpr/value.hh b/third_party/nix/src/libexpr/value.hh
index b5a1a33cba45..980d9affbb51 100644
--- a/third_party/nix/src/libexpr/value.hh
+++ b/third_party/nix/src/libexpr/value.hh
@@ -105,7 +105,10 @@ struct Value {
     NixFloat fpoint;
   };
 
-  Value() : type(tInt), integer(0) {}
+  Value() : type(tInt), attrs(nullptr) {
+    static_assert(offsetof(Value, attrs) + sizeof(attrs) == sizeof(Value));
+  }
+
   Value(const Value& copy);
   Value(Value&& move);
   ~Value() {}