Merge pull request #119 from trueNAHO/lib-each-default-system-pass-th…

…rough-each-system-pass-through-init

README.md

@@ -22,7 +22,7 @@ system = {
 ```
 It's mainly useful to
 detect typos and auto-complete if you use [rnix-lsp](https://github.com/nix-community/rnix-lsp).
-   
+
 Eg: instead of typing `"x86_64-linux"`, use `system.x86_64-linux`.
 
 
@@ -83,6 +83,11 @@ eachSystem allSystems (system: { hello = 42; })
 }
 ```
 
+### `eachSystemPassThrough :: [<system>] -> (<system> -> attrs)`
+
+Unlike `eachSystem`, this function does not inject the `${system}` key by merely
+providing the system argument to the function.
+
 ### `eachDefaultSystem :: (<system> -> attrs)`
 
 `eachSystem` pre-populated with `defaultSystems`.
@@ -113,6 +118,24 @@ eachSystem allSystems (system: { hello = 42; })
 }
 ```
 
+### `eachDefaultSystemPassThrough :: (<system> -> attrs)`
+
+`eachSystemPassThrough` pre-populated with `defaultSystems`.
+
+#### Example
+
+```nix
+inputs.flake-utils.lib.eachDefaultSystem (system: {
+  checks./*<SYSTEM>.*/"<CHECK>" = /* ... */;
+  devShells./*<SYSTEM>.*/"<DEV_SHELL>" = /* ... */;
+  packages./*<SYSTEM>.*/"<PACKAGE>" = /* ... */;
+})
+// inputs.flake-utils.lib.eachDefaultSystemPassThrough (system: {
+  homeConfigurations."<HOME_CONFIGURATION>" = /* ... */;
+  nixosConfigurations."<NIXOS_CONFIGURATION>" = /* ... */;
+})
+```
+
 ### `meld :: attrs -> [ path ] -> attrs`
 
 Meld merges subflakes using common inputs.  Useful when you want to

lib.nix

@@ -26,33 +26,47 @@ let
   # eachSystem using defaultSystems
   eachDefaultSystem = eachSystem defaultSystems;
 
-  # Builds a map from <attr>=value to <attr>.<system>=value for each system
-  #
-  eachSystem = systems: f:
+  # eachSystemPassThrough using defaultSystems
+  eachDefaultSystemPassThrough = eachSystemPassThrough defaultSystems;
+
+  # Builds a map from <attr>=value to <attr>.<system>=value for each system.
+  eachSystem = eachSystemOp (
+    # Merge outputs for each system.
+    f: attrs: system:
     let
-      # Merge together the outputs for all systems.
-      op = attrs: system:
-        let
-          ret = f system;
-          op = attrs: key: attrs //
-              {
-                ${key} = (attrs.${key} or { })
-                  // { ${system} = ret.${key}; };
-              }
-          ;
-        in
-        builtins.foldl' op attrs (builtins.attrNames ret);
+      ret = f system;
     in
-    builtins.foldl' op { }
-      (systems
-       ++ # add the current system if --impure is used
-          (if builtins?currentSystem then
-             if builtins.elem builtins.currentSystem systems
-             then []
-             else [ builtins.currentSystem ]
-           else
-             []))
-  ;
+    builtins.foldl' (
+      attrs: key:
+      attrs
+      // {
+        ${key} = (attrs.${key} or { }) // {
+          ${system} = ret.${key};
+        };
+      }
+    ) attrs (builtins.attrNames ret)
+  );
+
+  # Applies a merge operation accross systems.
+  eachSystemOp =
+    op: systems: f:
+    builtins.foldl' (op f) { } (
+      if
+        !builtins ? currentSystem || builtins.elem builtins.currentSystem systems
+      then
+        systems
+      else
+        # Add the current system if the --impure flag is used.
+        systems ++ [ builtins.currentSystem ]
+    );
+
+  # Merely provides the system argument to the function.
+  #
+  # Unlike eachSystem, this function does not inject the `${system}` key.
+  eachSystemPassThrough = eachSystemOp (
+    f: attrs: system:
+    attrs // (f system)
+  );
 
   # eachSystemMap using defaultSystems
   eachDefaultSystemMap = eachSystemMap defaultSystems;
@@ -198,9 +212,11 @@ let
       check-utils
       defaultSystems
       eachDefaultSystem
-      eachSystem
       eachDefaultSystemMap
+      eachDefaultSystemPassThrough
+      eachSystem
       eachSystemMap
+      eachSystemPassThrough
       filterPackages
       flattenTree
       meld