feat: add demo templates for flake-parts, bare-flake, and no-flake usage

flake-parts: full feature showcase with import-tree, treefmt, formatters,
onChange hooks, per-file overrides, and both APIs.

bare-flake: vanilla flake with evalModules, no flake-parts dependency.

no-flake: pure default.nix with import, no flake infrastructure.

Author: sini

templates/bare-flake/flake.nix

@@ -0,0 +1,66 @@
+# Vanilla flake using files via evalModules — no flake-parts dependency.
+{
+  inputs = {
+    files.url = "github:sini/files";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  };
+
+  outputs =
+    {
+      self,
+      files,
+      nixpkgs,
+      ...
+    }:
+    let
+      system = "x86_64-linux";
+      pkgs = nixpkgs.legacyPackages.${system};
+      eval = pkgs.lib.evalModules {
+        modules = [
+          files.module
+          {
+            config._module.args = {
+              inherit pkgs;
+            };
+            config.files.root = self;
+            config.files.generateApp = true;
+
+            # --- files.file attrset API ---
+            config.files.file.".gitignore".text = ''
+              result
+              .direnv
+            '';
+
+            config.files.file."README.md".text = ''
+              # bare-flake demo
+              Uses `evalModules` with `files.module` directly.
+            '';
+
+            config.files.file."scripts/hello.sh" = {
+              text = ''
+                #!/bin/sh
+                echo "hello from bare flake!"
+              '';
+              executable = true;
+            };
+
+            # --- files.files list API ---
+            config.files.files = [
+              {
+                path = "data/version.txt";
+                drv = pkgs.writeText "version.txt" "0.1.0";
+              }
+            ];
+          }
+        ];
+      };
+    in
+    {
+      checks.${system} = eval.config.files.checks;
+      packages.${system}.write-files = eval.config.files.writer.drv;
+      apps.${system}.write-files = {
+        type = "app";
+        program = pkgs.lib.getExe eval.config.files.writer.drv;
+      };
+    };
+}

templates/flake-parts/flake.nix

@@ -0,0 +1,25 @@
+{
+  inputs = {
+    files.url = "github:sini/files";
+
+    flake-parts = {
+      url = "github:hercules-ci/flake-parts";
+      inputs.nixpkgs-lib.follows = "nixpkgs";
+    };
+
+    import-tree = {
+      url = "github:vic/import-tree";
+      flake = false;
+    };
+
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+
+    treefmt-nix = {
+      url = "github:numtide/treefmt-nix";
+      flake = false;
+    };
+  };
+
+  outputs =
+    inputs: inputs.flake-parts.lib.mkFlake { inherit inputs; } ((import inputs.import-tree) ./modules);
+}

templates/flake-parts/modules/default.nix

@@ -0,0 +1,14 @@
+{ inputs, ... }:
+{
+  imports = [
+    inputs.files.flakeModule
+    (inputs.treefmt-nix + "/flake-module.nix")
+  ];
+
+  systems = [
+    "x86_64-linux"
+    "aarch64-linux"
+    "aarch64-darwin"
+    "x86_64-darwin"
+  ];
+}

templates/flake-parts/modules/files.nix

@@ -0,0 +1,75 @@
+# Demonstrates files.file attrset API, treefmt integration,
+# global formatters, per-file format overrides, and onChange hooks.
+{
+  perSystem =
+    { pkgs, ... }:
+    {
+      files.generateApp = true;
+
+      # --- treefmt integration ---
+      # all files.file entries are auto-formatted through treefmt
+      treefmt.programs.nixfmt.enable = true;
+      files.treefmt.enable = true;
+
+      # --- global formatter by extension ---
+      # applied to all .json files unless overridden per-file
+      files.formatters.json =
+        name: drv:
+        pkgs.runCommand "jqfmt-${name}" { nativeBuildInputs = [ pkgs.jq ]; } ''
+          jq --sort-keys . < ${drv} > $out
+        '';
+
+      # --- files.file attrset API ---
+
+      # text content — auto-formatted by nixfmt via treefmt
+      files.file."config.nix".text = "{foo=1;bar=2;}";
+
+      # source from structured data — formatted by global .json formatter
+      files.file."data/config.json".source = pkgs.writers.writeJSON "config.json" {
+        version = 1;
+        features = {
+          treefmt = true;
+          formatters = true;
+        };
+      };
+
+      # executable script
+      files.file."scripts/greet.sh" = {
+        text = ''
+          #!/bin/sh
+          echo "hello from files!"
+        '';
+        executable = true;
+      };
+
+      # onChange hook with runtimeInputs
+      files.file.".envrc" = {
+        text = "use flake";
+        onChange = {
+          runtimeInputs = [ pkgs.direnv ];
+          script = "direnv allow || true";
+        };
+      };
+
+      # per-file format override — takes priority over treefmt and global formatters
+      files.file."NOTICE".text = "generated by files";
+      files.file."NOTICE".format =
+        name: drv:
+        pkgs.runCommand "upper-${name}" { } ''
+          tr '[:lower:]' '[:upper:]' < ${drv} > $out
+        '';
+
+      # disable a file (useful for overriding shared module defaults)
+      files.file."disabled-example.txt".text = "this won't be written";
+      files.file."disabled-example.txt".enable = false;
+
+      # --- files.files list API ---
+      # both APIs can be used together; list entries merge with attrset entries
+      files.files = [
+        {
+          path = "data/version.txt";
+          drv = pkgs.writeText "version.txt" "0.1.0";
+        }
+      ];
+    };
+}

templates/no-flake/default.nix

@@ -0,0 +1,46 @@
+# No-flake usage: import files/module.nix directly with evalModules.
+# Run: nix-build -A writer && ./result/bin/write-files
+# Check: nix-build -A checks
+{
+  pkgs ? import <nixpkgs> { },
+  files ? builtins.fetchGit {
+    url = "https://github.com/sini/files";
+    ref = "main";
+  },
+  root ? ./.,
+}:
+let
+  eval = pkgs.lib.evalModules {
+    modules = [
+      (files + "/module.nix")
+      {
+        config._module.args = {
+          inherit pkgs;
+        };
+        config.files.root = root;
+
+        # --- files.file attrset API ---
+        config.files.file.".gitignore".text = ''
+          result
+        '';
+
+        config.files.file."README.md".text = ''
+          # no-flake demo
+          Uses `import` and `evalModules` — no flake required.
+        '';
+
+        # --- files.files list API ---
+        config.files.files = [
+          {
+            path = "data/version.txt";
+            drv = pkgs.writeText "version.txt" "0.1.0";
+          }
+        ];
+      }
+    ];
+  };
+in
+{
+  inherit (eval.config.files) checks;
+  writer = eval.config.files.writer.drv;
+}