lib.uuidFrom: generate a deterministic UUID

flake.nix

@@ -124,6 +124,19 @@
                 "abort generators.toDhall: unhandled value (${x})";
           };
 
+          uuidFrom = seed:
+            let digest = builtins.hashString "sha256" seed;
+            in (lib.lists.foldl ({ str, off }:
+              n:
+              let chunk = builtins.substring off n digest;
+              in {
+                str = if off == 0 then chunk else "${str}-${chunk}";
+                off = off + n;
+              }) {
+                str = "";
+                off = 0;
+              } [ 8 4 4 4 12 ]).str;
+
           nixosSystem =
             # A derivative of the function for generating Linux NixOS systems.
             # This one is not so well tested…