refactor(nix): isolate closure* to its own file

nix/modules/flake-parts/extra/default.nix

@@ -0,0 +1,5 @@
+{
+  imports = [
+    ./small-closure.nix
+  ];
+}

nix/modules/flake-parts/extra/small-closure.nix

@@ -0,0 +1,55 @@
+# To make sure that Emanote's closure size is small.
+{ root, inputs, ... }:
+let
+  allowedSystems = [ "x86_64-linux" "aarch64-darwin" ];
+in
+{
+  perSystem = { pkgs, lib, config, system, ... }: lib.mkIf (lib.elem system allowedSystems) {
+    haskellProjects.default = {
+      settings = {
+        emanote = { name, pkgs, self, super, ... }: {
+          separateBinOutput = false; # removeReferencesTo.nix doesn't work otherwise
+          justStaticExecutables = true;
+          removeReferencesTo = [
+            self.ghc
+            self.pandoc
+            self.pandoc-types
+            self.warp
+          ];
+        };
+      };
+    };
+
+    apps.check-closure-size = rec {
+      inherit (program) meta;
+      program = pkgs.writeShellApplication {
+        name = "emanote-check-closure-size";
+        runtimeInputs = [ pkgs.jq pkgs.bc pkgs.nix ];
+        meta.description = "Check that emanote's nix closure size remains reasonably small";
+        text = ''
+          MAX_CLOSURE_SIZE=$(echo "600 * 1000000" | bc)
+          CLOSURE_SIZE=$(nix path-info --json -S .#default | jq 'first(.[])'.closureSize)
+          echo "Emanote closure size: $CLOSURE_SIZE"
+          echo "    Max closure size: $MAX_CLOSURE_SIZE"
+          if [ "$CLOSURE_SIZE" -gt "$MAX_CLOSURE_SIZE" ]; then
+              echo "ERROR: Emanote's nix closure size has increased"
+              exit 3
+          else
+              echo "OK: Emanote's nix closure size is within limits"
+          fi
+        '';
+      };
+    };
+  };
+
+  flake.om.ci.default.emanote = {
+    dir = ".";
+    steps.custom = {
+      closure-size = {
+        type = "app";
+        name = "check-closure-size";
+        systems = allowedSystems;
+      };
+    };
+  };
+}

nix/modules/flake-parts/haskell.nix

@@ -44,13 +44,6 @@
         emanote = { name, pkgs, self, super, ... }: {
           check = false;
           extraBuildDepends = [ pkgs.stork ];
-          separateBinOutput = false; # removeReferencesTo.nix doesn't work otherwise
-          justStaticExecutables = true;
-          removeReferencesTo = [
-            self.pandoc
-            self.pandoc-types
-            self.warp
-          ];
           custom = pkg: pkg.overrideAttrs (lib.addMetaAttrs {
             # https://github.com/NixOS/cabal2nix/issues/608
             longDescription = ''
@@ -68,25 +61,5 @@
 
     packages.default = config.packages.emanote;
     apps.default = config.apps.emanote;
-    apps.check-closure-size = rec {
-      inherit (program) meta;
-      program = pkgs.writeShellApplication {
-        name = "emanote-check-closure-size";
-        runtimeInputs = [ pkgs.jq pkgs.bc pkgs.nix ];
-        meta.description = "Check that emanote's nix closure size remains reasonably small";
-        text = ''
-          MAX_CLOSURE_SIZE=$(echo "600 * 1000000" | bc)
-          CLOSURE_SIZE=$(nix path-info --json -S .#default | jq 'first(.[])'.closureSize)
-          echo "Emanote closure size: $CLOSURE_SIZE"
-          echo "    Max closure size: $MAX_CLOSURE_SIZE"
-          if [ "$CLOSURE_SIZE" -gt "$MAX_CLOSURE_SIZE" ]; then
-              echo "ERROR: Emanote's nix closure size has increased"
-              exit 3
-          else
-              echo "OK: Emanote's nix closure size is within limits"
-          fi
-        '';
-      };
-    };
   };
 }

nix/modules/flake-parts/toplevel.nix

@@ -7,18 +7,5 @@
       description = "A simple flake.nix template for emanote notebooks";
       path = builtins.path { path = inputs.emanote-template; filter = path: _: baseNameOf path == "flake.nix"; };
     };
-    om = {
-      ci.default = {
-        emanote = {
-          dir = ".";
-          steps.custom = {
-            closure-size = {
-              type = "app";
-              name = "check-closure-size";
-            };
-          };
-        };
-      };
-    };
   };
 }