build: package for nix flake

.gitignore

@@ -45,3 +45,4 @@ build/
 # uv virtualenv, at the repository root because pyproject.toml is there
 .venv/
 __pycache__/
+result

Dockerfile

@@ -1,5 +1,12 @@
 FROM golang:1.26-alpine3.24 AS build
 
+# VERSION and COMMIT are baked into the binary at build time via the -ldflags
+# below. Defaults mirror flake.nix and CI. The .git directory is excluded from
+# the build context, so the real commit has to be supplied by the host, e.g.:
+#   docker build --build-arg COMMIT=$(git rev-parse HEAD) .
+ARG VERSION=0.0.1-alpha
+ARG COMMIT=dev
+
 WORKDIR /app
 
 ENV CGO_ENABLED=0
@@ -11,7 +18,9 @@ COPY . .
 
 RUN --mount=type=cache,target=/root/.cache/go-build \
     --mount=type=cache,target=/go/pkg/mod \
-    go build -trimpath -ldflags="-s -w" -o /output/pen-bot ./cmd/pen-fun
+    go build -trimpath \
+    -ldflags="-s -w -X github.com/Neon-Genesis-Linux/pen-bot/internal/core.Version=${VERSION} -X github.com/Neon-Genesis-Linux/pen-bot/internal/core.Commit=${COMMIT}" \
+    -o /output/pen-bot ./cmd/pen-fun
 
 # The database lives on a volume mounted here. The directory is created in
 # this stage so that it can be given to the unprivileged user the runtime

compose.yaml

@@ -1,6 +1,13 @@
 services:
   app:
-    build: .
+    build:
+      context: .
+      # VERSION and COMMIT are baked into the binary via -ldflags in the
+      # Dockerfile. Defaults match flake.nix/CI; override from the host, e.g.:
+      #   COMMIT=$(git rev-parse HEAD) docker compose build
+      args:
+        VERSION: ${VERSION:-0.0.1-alpha}
+        COMMIT: ${COMMIT:-dev}
     pull_policy: build
     env_file:
       - .env

flake.nix

@@ -3,13 +3,58 @@
     nixpkgs.url = "https://channels.nixos.org/nixpkgs-unstable/nixexprs.tar.xz";
   };
 
-  outputs = {nixpkgs, ...}: let
+  outputs = inputs: let
+    nixpkgs = inputs.nixpkgs;
+    lib = nixpkgs.lib;
     systems = ["x86_64-linux" "aarch64-linux" "aarch64-darwin"];
-    forAllSystems = f: nixpkgs.lib.genAttrs systems (system: f nixpkgs.legacyPackages.${system});
+    version = "0.0.1-alpha";
+    commit =
+      if (builtins.hasAttr "self" inputs) && inputs.self != null
+      && (builtins.hasAttr "rev" inputs.self)
+      then inputs.self.rev
+      else "dev";
+    # Vendored dependency-tree hash. Obtained via vendorHash = lib.fakeHash;
+    # then reading the reported value and confirming a full `nix build`.
+    vendorHash = "sha256-QMHsT94FBrbhFOmfHdu8+EmqG+eMLlYZHGKLxuW9Fmk=";
+
+    # Only ship first-party Go code and its module files to the build. The
+    # gitignored dev artifacts `custom-gcl` (~55 MB) and `.venv` are excluded so
+    # the hermetic derivation stays small. `lib.fileset` is used instead of
+    # `filterSource`: the `builtins.filterSource` primop is unreliable here.
+    src =
+      let
+        repo = ./.;
+      in
+        lib.fileset.toSource {
+          root = repo;
+          fileset =
+            lib.fileset.unions [
+              (lib.fileset.fromSource (repo + "/go.mod"))
+              (lib.fileset.fromSource (repo + "/go.sum"))
+              (lib.fileset.fromSource (repo + "/cmd"))
+              (lib.fileset.fromSource (repo + "/internal"))
+            ];
+        };
+
+    buildPen = pkgs: pkgs.buildGoModule {
+      pname = "pen-fun";
+      version = version;
+      src = src;
+      subPackages = [ "cmd/pen-fun" ];
+      vendorHash = vendorHash;
+      ldflags = [
+        "-s"
+        "-w"
+        "-X"
+        "github.com/Neon-Genesis-Linux/pen-bot/internal/core.Version=${version}"
+        "-X"
+        "github.com/Neon-Genesis-Linux/pen-bot/internal/core.Commit=${commit}"
+      ];
+    };
   in {
-    devShells = forAllSystems (pkgs: {
-      default = pkgs.mkShell {
-        packages = with pkgs; [
+    devShells = lib.genAttrs systems (system: {
+      default = nixpkgs.legacyPackages.${system}.mkShell {
+        packages = with nixpkgs.legacyPackages.${system}; [
           go_1_26
           golangci-lint
           gofumpt
@@ -19,7 +64,19 @@
           yamlfmt
           dockerfmt
         ];
+        # custom-gcl (golangci-lint + NilAway) is built from .custom-gcl.yml at
+        # activation, mirroring .github/workflows/ci.yml. Network is available in
+        # a dev shell, and the guard skips rebuilding when it already exists.
+        shellHook = ''
+          if [ ! -x ./custom-gcl ]; then
+            golangci-lint custom
+          fi
+        '';
       };
     });
+
+    packages = lib.genAttrs systems (system: {
+      default = buildPen nixpkgs.legacyPackages.${system};
+    });
   };
 }

internal/core/start.go

@@ -17,12 +17,13 @@ import (
 	"github.com/Neon-Genesis-Linux/pen-bot/internal/db"
 )
 
-// Start connects the bot to Discord, syncs the registered commands, and blocks
-// until ctx is cancelled or the process is interrupted. It reads the intents
-// and command definitions once, at startup, so anything registered afterwards
-// has no effect.
+var (
+	Version = "dev"
+	Commit  = "dev"
+)
+
 func Start(ctx context.Context, token string, guildIDs []snowflake.ID) error {
-	slog.Info("starting pen bot...")
+	slog.Info("starting pen bot...", "version", Version, "commit", Commit)
 	slog.Info("disgo version", slog.String("version", disgo.Version))
 
 	if len(guildIDs) > 0 {