Add nix flake support

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -1 +1,5 @@
 /target
+result
+result-*
+*.tmp
+.direnv/

flake.nix

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+{
+  description = "trivia on the command line";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    utils.url = "github:numtide/flake-utils";
+    rust-overlay.url = "github:oxalica/rust-overlay";
+    crate2nix = {
+      url = "github:kolloch/crate2nix";
+      flake = false;
+    };
+    flake-compat = {
+      url = "github:edolstra/flake-compat";
+      flake = false;
+    };
+  };
+
+  outputs = { self, nixpkgs, utils, rust-overlay, crate2nix, ... }:
+    let
+      name = "oi";
+    in
+    utils.lib.eachDefaultSystem
+      (system:
+        let
+          # Imports
+          pkgs = import nixpkgs {
+            inherit system;
+            overlays = [
+              rust-overlay.overlays.default
+              (self: super: {
+                # Because rust-overlay bundles multiple rust packages into one
+                # derivation, specify that mega-bundle here, so that crate2nix
+                # will use them automatically.
+                rustc = self.rust-bin.stable.latest.default;
+                cargo = self.rust-bin.stable.latest.default;
+              })
+            ];
+          };
+          inherit (import "${crate2nix}/tools.nix" { inherit pkgs; })
+            generatedCargoNix;
+
+          # Create the cargo2nix project
+          project = pkgs.callPackage
+            (generatedCargoNix {
+              inherit name;
+              src = ./.;
+            })
+            {
+              # Individual crate overrides go here
+              # Example: https://github.com/balsoft/simple-osd-daemons/blob/6f85144934c0c1382c7a4d3a2bbb80106776e270/flake.nix#L28-L50
+              defaultCrateOverrides = pkgs.defaultCrateOverrides // {
+                # The app crate itself is overriden here. Typically we
+                # configure non-Rust dependencies (see below) here.
+                ${name} = oldAttrs: {
+                  inherit buildInputs nativeBuildInputs;
+                } // buildEnvVars;
+              };
+            };
+
+          # Configuration for the non-Rust dependencies
+          buildInputs = with pkgs; [ openssl.dev ];
+          nativeBuildInputs = with pkgs; [ rustc cargo pkgconfig nixpkgs-fmt ];
+          buildEnvVars = {
+            PKG_CONFIG_PATH = "${pkgs.openssl.dev}/lib/pkgconfig";
+          };
+        in
+        rec {
+          packages.${name} = project.rootCrate.build;
+
+          # `nix build`
+          defaultPackage = packages.${name};
+
+          # `nix run`
+          apps.${name} = utils.lib.mkApp {
+            inherit name;
+            drv = packages.${name};
+          };
+          defaultApp = apps.${name};
+
+          # `nix develop`
+          devShell = pkgs.mkShell
+            {
+              inherit buildInputs nativeBuildInputs;
+              RUST_SRC_PATH = "${pkgs.rust.packages.stable.rustPlatform.rustLibSrc}";
+            } // buildEnvVars;
+        }
+      );
+}