flake: partition dev dependencies

This removes the need for end-users to manually set
`nixvim.inputs.devshell.follows = ""` (etc)

We offload evaluation of some of our flake modules into a `dev`
partition submodule.
- When its not needed, this submodule is not evaluated.
- When it is needed, it fetches extra inputs from `flake/dev/flake.nix`
  as part of evaluating the submodule.

See https://flake.parts/options/flake-parts-partitions.html

.github/workflows/update.yml

@@ -6,10 +6,14 @@ on:
   # Allow manual triggering
   workflow_dispatch:
     inputs:
-      lock:
+      root_lock:
         type: boolean
         default: true
-        description: Update flake.lock
+        description: Update root flake.lock
+      dev_lock:
+        type: boolean
+        default: true
+        description: Update dev flake.lock
       generate:
         type: boolean
         default: true
@@ -100,9 +104,9 @@ jobs:
           git fetch origin "$pr_branch"
           git branch --set-upstream-to "origin/$pr_branch"
 
-      - name: Update flake.lock
-        id: flake_lock
-        if: inputs.lock || github.event_name == 'schedule'
+      - name: Update root flake.lock
+        id: root_flake_lock
+        if: inputs.root_lock || github.event_name == 'schedule'
         run: |
           old=$(git show --no-patch --format=%h)
           nix flake update --commit-lock-file
@@ -113,6 +117,22 @@ jobs:
             echo "EOF" >> "$GITHUB_OUTPUT"
           fi
 
+      - name: Update dev flake.lock
+        id: dev_flake_lock
+        if: inputs.dev_lock || github.event_name == 'schedule'
+        run: |
+          root_nixpkgs=$(nix eval -f . 'inputs.nixpkgs.rev')
+          old=$(git show --no-patch --format=%h)
+          nix flake update --commit-lock-file \
+              --override-input nixpkgs "github:NixOS/nixpkgs/$root_nixpkgs" \
+              --flake './flake/dev'
+          new=$(git show --no-patch --format=%h)
+          if [ "$old" != "$new" ]; then
+            echo "body<<EOF" >> "$GITHUB_OUTPUT"
+            git show --no-patch --format=%b >> "$GITHUB_OUTPUT"
+            echo "EOF" >> "$GITHUB_OUTPUT"
+          fi
+
       - name: Update generated files
         id: generate
         if: inputs.generate || github.event_name == 'schedule'
@@ -185,9 +205,14 @@ jobs:
           title: |
             [${{ github.ref_name }}] Update flake.lock & generated files
           body: |
-            ## Flake lockfile
+            ## Root lockfile
+            ```
+            ${{ steps.root_flake_lock.outputs.body || 'No changes' }}
+            ```
+
+            ## Dev lockfile
             ```
-            ${{ steps.flake_lock.outputs.body || 'No changes' }}
+            ${{ steps.dev_flake_lock.outputs.body || 'No changes' }}
             ```
 
             ## Generate

default.nix

@@ -1,6 +1,6 @@
 (import (
   let
-    lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+    lock = builtins.fromJSON (builtins.readFile ./flake/dev/flake.lock);
   in
   fetchTarball {
     url =

flake.nix

@@ -9,60 +9,10 @@
       inputs.nixpkgs-lib.follows = "nixpkgs";
     };
 
-    /*
-      # NOTE: The inputs below this comment are optional
-      # You can remove them with `inputs.<input>.follows = ""`
-
-      For example:
-
-      ```
-      nixvim = {
-        url = "github:nix-community/nixvim";
-        inputs = {
-          nixpkgs.follows = "nixpkgs";
-          flake-parts.follows = "flake-parts";
-
-          devshell.follows = "";
-          flake-compat.follows = "";
-          git-hooks.follows = "";
-          home-manager.follows = "";
-          nix-darwin.follows = "";
-          treefmt-nix.follows = "";
-        };
-      };
-      ```
-    */
-
     nuschtosSearch = {
       url = "github:NuschtOS/search";
       inputs.nixpkgs.follows = "nixpkgs";
     };
-
-    home-manager = {
-      url = "github:nix-community/home-manager";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-    nix-darwin = {
-      url = "github:lnl7/nix-darwin";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-
-    devshell = {
-      url = "github:numtide/devshell";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-    treefmt-nix = {
-      url = "github:numtide/treefmt-nix";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-
-    flake-compat.url = "https://flakehub.com/f/edolstra/flake-compat/1.tar.gz";
-
-    git-hooks = {
-      url = "github:cachix/git-hooks.nix";
-      inputs.nixpkgs.follows = "nixpkgs";
-      inputs.flake-compat.follows = "flake-compat";
-    };
   };
 
   nixConfig = {

flake/default.nix

@@ -1,14 +1,56 @@
+{
+  lib,
+  inputs,
+  config,
+  partitionStack,
+  ...
+}:
 {
   imports = [
-    ./dev
     ./flake-modules
     ./lib.nix
     ./legacy-packages.nix
     ./nixvim-configurations.nix
     ./overlays.nix
     ./packages.nix
     ./templates.nix
-    ./tests.nix
     ./wrappers.nix
+    inputs.flake-parts.flakeModules.partitions
   ];
+
+  # Define flake partitions
+  # Each has a `module`, assigned to the partition's submodule,
+  # and an `extraInputsFlake`, used for its inputs.
+  # See https://flake.parts/options/flake-parts-partitions.html
+  partitions = {
+    dev = {
+      module = ./dev;
+      extraInputsFlake = ./dev;
+    };
+  };
+
+  # Specify which outputs are defined by which partitions
+  partitionedAttrs = {
+    checks = "dev";
+    devShells = "dev";
+    formatter = "dev";
+  };
+
+  # For any output attrs normally defined by the root flake configuration,
+  # any exceptions must be manually propagated from the `dev` partition.
+  #
+  # NOTE: Attrs should be explicitly propagated at the deepest level.
+  # Otherwise the partition won't be lazy, making it pointless.
+  # E.g. propagate `packages.${system}.foo` instead of `packages.${system}`
+  # See: https://github.com/hercules-ci/flake-parts/issues/258
+  perSystem =
+    { system, ... }:
+    {
+      packages = lib.optionalAttrs (partitionStack == [ ]) {
+        # Propagate `packages` from the `dev` partition:
+        inherit (config.partitions.dev.module.flake.packages.${system})
+          list-plugins
+          ;
+      };
+    };
 }