Merge pull request #242 from hercules-ci/partition

Partitions

ci.nix

@@ -1,12 +0,0 @@
-# We're doing things a bit differently because Nix doesn't let us
-# split out the dev dependencies and subflakes are broken, let alone "superflakes".
-# See dev/README.md
-let
-  flake = import ./dev;
-  inherit (flake.inputs.nixpkgs) lib;
-in
-{
-  inherit (flake) herculesCI;
-} // {
-  checks = lib.recurseIntoAttrs flake.checks.${builtins.currentSystem};
-}

dev/README.md

@@ -1,6 +0,0 @@
-
-# Separate `dev` flake
-
-Wouldn't recommend this pattern normally, but I'm trying to keep
-deps low for `flake-parts` until we have split dev inputs
-that don't carry over to dependent lock files.

dev/default.nix

@@ -1,16 +0,0 @@
-let
-  flake = builtins.getFlake (toString ./.);
-  fmc-lib = (builtins.getFlake (toString ../.)).lib;
-  args = {
-    inherit self;
-  } // flake.inputs;
-  self = {
-    inherit (flake) inputs;
-    outPath = ../.; # used by pre-commit module, etc
-    outputs = self.config.flake;
-  } //
-  fmc-lib.mkFlake
-    { inputs = args; }
-    ./flake-module.nix;
-in
-self.config.flake // { inherit (flake) inputs; }

dev/flake.nix

@@ -3,7 +3,7 @@
 
   inputs = {
     # Flakes don't give us a good way to depend on .., so we don't.
-    # As a consequence, this flake is a little non-standard, and
+    # As a consequence, this flake only provides dependencies, and
     # we can't use the `nix` CLI as expected.
 
     nixpkgs.url = "github:NixOS/nixpkgs";
@@ -16,5 +16,6 @@
     {
       # The dev tooling is in ./flake-module.nix
       # See comment at `inputs` above.
+      # It is loaded into partitions.dev by the root flake.
     };
 }

dev/repl.nix

@@ -1,3 +0,0 @@
-# convenience for loading into nix repl
-let self = builtins.getFlake (toString ./.);
-in self // { inherit self; }

extras/partitions.nix

@@ -0,0 +1,130 @@
+{ lib, config, inputs, extendModules, partitionStack, self, ... }:
+let
+  inherit (lib)
+    literalMD
+    mapAttrs
+    mkOption
+    optionalAttrs
+    types
+    ;
+
+  partitionModule = { config, options, name, ... }: {
+    options = {
+      extraInputsFlake = mkOption {
+        type = types.raw;
+        default = { };
+        description = ''
+          Location of a flake whose inputs to add to the inputs module argument in the partition.
+        '';
+      };
+      extraInputs = mkOption {
+        type = types.lazyAttrsOf types.raw;
+        description = ''
+          Extra inputs to add to the inputs module argument in the partition.
+
+          This can be used as a workaround for the fact that transitive inputs are locked in the "end user" flake.
+          That's not desirable for inputs they don't need, such as development inputs.
+        '';
+        default = { };
+        defaultText = literalMD ''
+          if `extraInputsFlake` is set, then `builtins.getFlake extraInputsFlake`, else `{ }`
+        '';
+      };
+      module = mkOption {
+        type = (extendModules {
+          specialArgs =
+            let
+              inputs2 = inputs // config.extraInputs // {
+                self = self2;
+              };
+              self2 = self // {
+                inputs = inputs2;
+              };
+            in
+            {
+              inputs = inputs2;
+              self = self2;
+              partitionStack = partitionStack ++ [ name ];
+            };
+        }).type;
+        default = { };
+        description = ''
+          A re-evaluation of the flake-parts top level modules.
+
+          You may define config definitions, imports, etc here, and it can be read like any other submodule.
+        '';
+      };
+    };
+    config = {
+      extraInputs = lib.mkIf options.extraInputsFlake.isDefined (
+        let
+          p = options.extraInputsFlake.value;
+          flake =
+            if builtins.typeOf p == "path"
+            then get-flake p
+            else builtins.getFlake p;
+        in
+        flake.inputs
+      );
+    };
+  };
+
+  # Nix does not recognize that a flake like "${./dev}", which is a content
+  # addressed store path is a pure input, so we have to fetch and wire it
+  # manually with get-flake.
+  # TODO: update this
+  get-flake = import (builtins.fetchTree {
+    type = "github";
+    owner = "ursi";
+    repo = "get-flake";
+    rev = "a6c57417d1b857b8be53aba4095869a0f438c502";
+  });
+
+in
+{
+  options = {
+    partitionedAttrs = mkOption {
+      type = types.attrsOf types.str;
+      default = { };
+      description = ''
+        A set of flake output attributes that are taken from a partition instead of the default top level flake-parts evaluation.
+
+        The attribute name refers to the flake output attribute name, and the value is the name of the partition to use.
+
+        The flake attributes are overridden with `lib.mkForce` priority.
+
+        See the `partitions` options to understand the purpose.
+      '';
+    };
+    partitions = mkOption {
+      type = types.attrsOf (types.submodule partitionModule);
+      default = { };
+      description = ''
+        By partitioning the flake, you can avoid fetching inputs that are not
+        needed for the evaluation of a particular attribute.
+
+        Each partition is a distinct module system evaluation. This allows
+        attributes of the final flake to be defined by multiple sets of modules,
+        so that for example the `packages` attribute can be evaluated without
+        loading development related inputs.
+
+        While the module system does a good job at preserving laziness, the fact
+        that a development related import can define `packages` means that
+        in order to evaluate `packages`, you need to evaluate at least to the
+        point where you can conclude that the development related import does
+        not actually define a `packages` attribute. While the actual evaluation
+        is cheap, it can only happen after fetching the input, which is not
+        as cheap.
+      '';
+    };
+  };
+  config = {
+    # Default, overriden with specialArgs inside partitions.
+    _module.args.partitionStack = [ ];
+    flake = optionalAttrs (partitionStack == [ ]) (
+      mapAttrs
+        (attrName: partition: lib.mkForce (config.partitions.${partition}.module.flake.${attrName}))
+        config.partitionedAttrs
+    );
+  };
+}

flake.nix

@@ -5,7 +5,8 @@
     nixpkgs-lib.url = "https://github.com/NixOS/nixpkgs/archive/a5d394176e64ab29c852d03346c1fc9b0b7d33eb.tar.gz"; # 9f918d616c5321ad374ae6cb5ea89c9e04bf3e58 /lib from nixos-unstable
   };
 
-  outputs = { nixpkgs-lib, ... }: {
+  outputs = inputs@{ nixpkgs-lib, ... }:
+    let
       lib = import ./lib.nix {
         inherit (nixpkgs-lib) lib;
         # Extra info for version check message
@@ -47,6 +48,22 @@
       flakeModules = {
         easyOverlay = ./extras/easyOverlay.nix;
         flakeModules = ./extras/flakeModules.nix;
+        partitions = ./extras/partitions.nix;
+      };
+    in
+    lib.mkFlake { inherit inputs; } {
+      systems = [ ];
+      imports = [ flakeModules.partitions ];
+      partitionedAttrs.checks = "dev";
+      partitionedAttrs.devShells = "dev";
+      partitionedAttrs.herculesCI = "dev";
+      partitions.dev.extraInputsFlake = ./dev;
+      partitions.dev.extraInputs.flake-parts = inputs.self;
+      partitions.dev.module = {
+        imports = [ ./dev/flake-module.nix ];
+      };
+      flake = {
+        inherit lib templates flakeModules;
       };
     };
 

shell.nix

@@ -1,2 +1 @@
-# non-idiomatic, see tools/README.md
-(import ./dev).devShells.${builtins.currentSystem}.default
+(builtins.getFlake ("git+file://" + toString ./.)).devShells.${builtins.currentSystem}.default