Merge pull request #2 from hercules-ci/template-and-readme

Freeform type for flake, template, readme update

README.md

@@ -5,52 +5,51 @@ _Foundational flake attributes represented using the module system._
 
 `flake-modules-core` provides common options for an ecosystem of modules to extend.
 
-This allows anyone to bundle up tooling into reusable modules.
+# Why Modules?
 
-For users, this makes Flakes easier to wire up.
+Flakes are configuration. The module system lets you refactor configuration
+into modules that can be shared.
 
-_Non-goals_:
- - Replace general Nix expressions, which are needed for advanced and/or ad-hoc use cases.
- - Accumulate everything into a single repository. As the name might suggest, it focuses only on options that have to do with well-known Nix Flakes attributes.
+It reduces the proliferation of custom Nix glue code, similar to what the
+module system has done for NixOS configurations.
 
+Unlike NixOS, but following Flakes' spirit, `flake-modules-core` is not a
+monorepo with the implied goal of absorbing all of open source, but rather
+a single module that other repositories can build upon, while ensuring a
+baseline level of compatibility: which core attribute make up a flake and
+how these are represented as module options.
 
-# Example Flake
+# Getting Started
 
-```nix
-{
-  description = "A very basic flake";
+If your project does not have a flake yet:
 
-  inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+```console
+nix flake init -t github:hercules-ci/flake-modules-core
+```
+
+Otherwise, add the input,
+
+```
     flake-modules-core.url = "github:hercules-ci/flake-modules-core";
     flake-modules-core.inputs.nixpkgs.follows = "nixpkgs";
-    devshell.url = "github:hercules-ci/devshell/flake-modules"; # credit to numtide
-  };
+```
 
-  outputs = { self, nixpkgs, flake-modules-core, devshell, ... }:
+then slide `evalFlakeModule` between your outputs function head and body,
+
+```
+  outputs = { self, flake-modules-core, ... }:
     (flake-modules-core.lib.evalFlakeModule
       { inherit self; }
       {
-        systems = [ "x86_64-linux" ];
-        imports = [
-          devshell.flakeModule
-        ];
         flake = {
-          nixosConfigurations.foo = lib.nixosSystem { /* ... */ };
-        };
-        perSystem = system: { config, pkgs, self', inputs', ... }: {
-          _module.args.pkgs = inputs'.nixpkgs.legacyPackages;
-          devshell.settings.commands = [
-            {
-              help = "format nix code";
-              package = pkgs.nixpkgs-fmt;
+          # Put your original flake attributes here.
         }
-          ];
-          packages.hello = pkgs.hello;
-          packages.hello2 = self'.packages.hello;
-          checks.hello = self'.packages.hello;
-        };
-      }).config.flake;
-
       }
+    ).config.flake;
 ```
+
+Now you can add the remaining module attributes like in the [the template](./template/flake.nix).
+
+# Example
+
+See [the template](./template/flake.nix).

all-modules.nix

@@ -3,6 +3,7 @@
   imports = [
     ./modules/checks.nix
     ./modules/devShell.nix
+    ./modules/flake.nix
     ./modules/legacyPackages.nix
     ./modules/packages.nix
     ./modules/perSystem.nix

flake.nix

@@ -7,8 +7,11 @@
 
   outputs = { self, nixpkgs, ... }: {
     lib = import ./lib.nix { inherit (nixpkgs) lib; };
-    flakeModules = {
-      core = ./all-modules.nix;
+    defaultTemplate = {
+      path = ./template;
+      description = ''
+        A minimal flake using flake-modules-core.
+      '';
     };
   };
 

lib.nix

@@ -16,6 +16,17 @@ let
         specialArgs = { inherit self flake-modules-core-lib; } // specialArgs;
         modules = [ ./all-modules.nix module ];
       };
+
+    # For extending options in an already declared submodule.
+    # Workaround for https://github.com/NixOS/nixpkgs/issues/146882
+    mkSubmoduleOptions =
+      options:
+      mkOption {
+        type = types.submoduleWith {
+          modules = [ { inherit options; } ];
         };
+      };
+  };
+
 in
 flake-modules-core-lib

modules/checks.nix

@@ -8,13 +8,19 @@ let
     optionalAttrs
     types
     ;
+  inherit (flake-modules-core-lib)
+    mkSubmoduleOptions
+    ;
 in
 {
   options = {
-    flake = {
+    flake = mkSubmoduleOptions {
       checks = mkOption {
         type = types.lazyAttrsOf (types.lazyAttrsOf types.package);
         default = { };
+        description = ''
+          Derivations to be built by nix flake check.
+        '';
       };
     };
   };
@@ -38,6 +44,9 @@ in
         checks = mkOption {
           type = types.lazyAttrsOf types.package;
           default = { };
+          description = ''
+            Derivations to be built by nix flake check.
+          '';
         };
       };
     };

modules/devShell.nix

@@ -8,13 +8,19 @@ let
     optionalAttrs
     types
     ;
+  inherit (flake-modules-core-lib)
+    mkSubmoduleOptions
+    ;
 in
 {
   options = {
-    flake = {
+    flake = mkSubmoduleOptions {
       devShell = mkOption {
         type = types.lazyAttrsOf types.package;
         default = { };
+        description = ''
+          For each system a derivation that nix develop bases its environment on.
+        '';
       };
     };
   };
@@ -37,6 +43,9 @@ in
       options = {
         devShell = mkOption {
           type = types.nullOr types.package;
+          description = ''
+            A derivation that nix develop bases its environment on.
+          '';
         };
       };
     };

modules/flake.nix

@@ -0,0 +1,27 @@
+{ config, lib, ... }:
+let
+  inherit (lib)
+    filterAttrs
+    genAttrs
+    mapAttrs
+    mkOption
+    optionalAttrs
+    types
+    ;
+in
+{
+  options = {
+    flake = mkOption {
+      type = types.submoduleWith {
+        modules = [
+          { freeformType = types.lazyAttrsOf types.anything; }
+        ];
+      };
+      description = ''
+        Raw flake attributes. Any attribute can be set here, but some
+        attributes are represented by options, to provide appropriate
+        configuration merging.
+      '';
+    };
+  };
+}

modules/legacyPackages.nix

@@ -8,13 +8,19 @@ let
     optionalAttrs
     types
     ;
+  inherit (flake-modules-core-lib)
+    mkSubmoduleOptions
+    ;
 in
 {
   options = {
-    flake = {
+    flake = mkSubmoduleOptions {
       legacyPackages = mkOption {
         type = types.lazyAttrsOf (types.lazyAttrsOf types.anything);
         default = { };
+        description = ''
+          Per system, an attribute set of anything. This is also used by nix build .#<attrpath>.
+        '';
       };
     };
   };
@@ -38,6 +44,9 @@ in
         legacyPackages = mkOption {
           type = types.lazyAttrsOf types.anything;
           default = { };
+          description = ''
+            An attribute set of anything. This is also used by nix build .#<attrpath>.
+          '';
         };
       };
     };

modules/packages.nix

@@ -8,13 +8,20 @@ let
     optionalAttrs
     types
     ;
+  inherit (flake-modules-core-lib)
+    mkSubmoduleOptions
+    ;
 in
 {
   options = {
-    flake = {
+    flake = mkSubmoduleOptions {
       packages = mkOption {
         type = types.lazyAttrsOf (types.lazyAttrsOf types.package);
         default = { };
+        description = ''
+          Per system an attribute set of packages.
+          nix build .#<name> will build packages.<system>.<name>.
+        '';
       };
     };
   };
@@ -38,6 +45,10 @@ in
         packages = mkOption {
           type = types.lazyAttrsOf types.package;
           default = { };
+          description = ''
+            An attribute set of packages to be built by nix build .#<name>.
+            nix build .#<name> will build packages.<name>.
+          '';
         };
       };
     };

modules/perSystem.nix

@@ -14,7 +14,6 @@ in
     systems = mkOption {
       description = "All the system types to enumerate in the flake.";
       type = types.listOf types.str;
-      default = [ ];
     };
 
     perInput = mkOption {

modules/self.nix

@@ -1,6 +0,0 @@
-{ lib, ... }: {
-  options.self = lib.mkOption {
-    description = "The current flake.";
-    type = type.lazyAttrsOf type.unspecified;
-  };
-}

template/flake.nix

@@ -0,0 +1,37 @@
+{
+  description = /* ... */;
+
+  inputs = {
+    flake-modules-core.url = "github:hercules-ci/flake-modules-core";
+    flake-modules-core.inputs.nixpkgs.follows = "nixpkgs";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
+
+  outputs = { self, flake-modules-core, ... }:
+    (flake-modules-core.lib.evalFlakeModule
+      { inherit self; }
+      {
+        imports = [
+          # To import a flake module
+          # 1. Add foo to inputs
+          # 2. Add foo as a parameter to the outputs function
+          # 3. Add here: foo.flakeModule
+
+        ];
+        systems = [ "x86_64-linux" "aarch64-darwin" ];
+        perSystem = system: { config, self', inputs', ... }: {
+          # Per-system attributes can be defined here. The self' and inputs'
+          # module parameters provide easy access to attributes of the same
+          # system.
+
+          packages.hello = inputs'.nixpkgs.legacyPackages.hello;
+        };
+        flake = {
+          # The usual flake attributes can be defined here, including system-
+          # agnostic ones like nixosModule and system-enumerating ones, although
+          # those are more easily expressed in perSystem.
+
+        };
+      }
+    ).config.flake;
+}