first draft

nix/module.nix

@@ -0,0 +1,109 @@
+# NixOS module: automatic nushell completion generation from manpages
+#
+# Modeled on nixpkgs' programs/fish.nix completion generator.
+# For each package in environment.systemPackages, a small derivation runs
+# `inshellah manpage-dir` against its share/man directory. Results are merged
+# into a single directory and placed in nushell's vendor autoload path.
+#
+# Usage in your NixOS configuration:
+#
+#   { pkgs, ... }: {
+#     imports = [ ./path/to/inshellah/nix/module.nix ];
+#     programs.inshellah.enable = true;
+#     # Optionally add packages not in systemPackages:
+#     # programs.inshellah.extraPackages = [ pkgs.kubectl ];
+#   }
+
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.programs.inshellah;
+
+  # The inshellah binary — override this if you build from the local flake
+  inshellahPkg = cfg.package;
+
+  # Per-package derivation: run inshellah manpage-dir against a package's manpages
+  generateCompletions = package:
+    pkgs.runCommandLocal
+      (let
+        inherit (lib.strings) stringLength substring storeDir;
+        storeLength = stringLength storeDir + 34;
+        pathName = substring storeLength (stringLength package - storeLength) package;
+      in
+        (package.name or pathName) + "_nu-completions"
+      )
+      ({
+        inherit package;
+        nativeBuildInputs = [ inshellahPkg ];
+      } // lib.optionalAttrs (package ? meta.priority) {
+        meta.priority = package.meta.priority;
+      })
+      ''
+        mkdir -p $out
+        if [ -d "$package/share/man" ]; then
+          inshellah manpage-dir "$package/share/man" > "$out/completions.nu" 2>/dev/null || true
+          # Remove empty files
+          find $out -empty -delete
+        fi
+      '';
+
+in {
+  options.programs.inshellah = {
+    enable = lib.mkEnableOption "nushell completion generation from manpages via inshellah";
+
+    package = lib.mkOption {
+      type = lib.types.package;
+      description = "The inshellah package to use for generating completions.";
+    };
+
+    extraPackages = lib.mkOption {
+      type = lib.types.listOf lib.types.package;
+      default = [];
+      description = ''
+        Additional packages to generate nushell completions from, beyond
+        those in {option}`environment.systemPackages`.
+      '';
+    };
+
+    generatedCompletionsPath = lib.mkOption {
+      type = lib.types.str;
+      default = "/share/nushell/vendor/autoload";
+      description = ''
+        Subdirectory within the merged environment where completion files
+        are placed. The default matches nushell's vendor autoload convention
+        (discovered via XDG_DATA_DIRS).
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    # Merge all per-package completions into a single directory.
+    # This path ends up in the system profile, and nushell discovers it
+    # via XDG_DATA_DIRS -> $prefix/share/nushell/vendor/autoload/
+    environment.pathsToLink = [ cfg.generatedCompletionsPath ];
+
+    environment.systemPackages = [
+      (pkgs.buildEnv {
+        name = "nushell-generated-completions";
+        ignoreCollisions = true;
+        paths = map generateCompletions (
+          config.environment.systemPackages ++ cfg.extraPackages
+        );
+        pathsToLink = [ "/" ];
+        # Nest everything under the vendor autoload path
+        postBuild = ''
+          if [ -d "$out" ]; then
+            tmp=$(mktemp -d)
+            cp -r "$out/"* "$tmp/" 2>/dev/null || true
+            rm -rf "$out/"*
+            mkdir -p "$out${cfg.generatedCompletionsPath}"
+            for f in "$tmp"/*.nu; do
+              [ -f "$f" ] && cp "$f" "$out${cfg.generatedCompletionsPath}/"
+            done
+            rm -rf "$tmp"
+          fi
+        '';
+      })
+    ];
+  };
+}