lib/systems/flake-systems: drop x86_64-darwin

flake.nix

@@ -220,17 +220,25 @@
         evaluation. Evaluating the attribute value tends to require a significant
         amount of computation, even considering lazy evaluation.
       */
-      legacyPackages = forAllSystems (
-        system:
-        (import ./. {
-          inherit system;
-          overlays = import ./pkgs/top-level/impure-overlays.nix ++ [
-            (final: prev: {
-              lib = prev.lib.extend libVersionInfoOverlay;
-            })
-          ];
-        })
-      );
+      legacyPackages =
+        let
+          # We include `x86_64-darwin` here to ensure that users get a
+          # good error message for the 26.11 deprecation of the platform,
+          # while excluding it from `lib.systems.flakeExposed` so that we
+          # don’t break `nix flake check` for downstream users.
+          forAllSystems' = lib.genAttrs (lib.systems.flakeExposed ++ [ "x86_64-darwin" ]);
+        in
+        forAllSystems' (
+          system:
+          (import ./. {
+            inherit system;
+            overlays = import ./pkgs/top-level/impure-overlays.nix ++ [
+              (final: prev: {
+                lib = prev.lib.extend libVersionInfoOverlay;
+              })
+            ];
+          })
+        );
 
       /**
         Optional modules that can be imported into a NixOS configuration.

lib/systems/flake-systems.nix

@@ -11,7 +11,6 @@
   "x86_64-linux"
   # Tier 2
   "aarch64-linux"
-  "x86_64-darwin"
   # Tier 3
   "armv6l-linux"
   "armv7l-linux"