Add hashed-mirrors back

Some users have their own hashed-mirrors setup, that is used to mirror
things in addition to what’s available on tarballs.nixos.org. Although
this should be feasable to do with a Binary Cache, it’s not always
easy, since you have to remember what "name" each of the tarballs has.
Continuing to support hashed-mirrors is cheap, so it’s best to leave
support in Nix. Note that NIX_HASHED_MIRRORS is also supported in
Nixpkgs through fetchurl.nix.

Note that this excludes tarballs.nixos.org from the default, as in
\#3689. All of these are available on cache.nixos.org.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index 3406a9331..e3bb4cf84 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -335,6 +335,9 @@ public:
         "setuid/setgid bits or with file capabilities."};
 #endif
 
+    Setting<Strings> hashedMirrors{this, {}, "hashed-mirrors",
+        "A list of servers used by builtins.fetchurl to fetch files by hash."};
+
     Setting<uint64_t> minFree{this, 0, "min-free",
         "Automatically run the garbage collector when free disk space drops below the specified amount."};