place scaffolding that enables cargo and nix builds

Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "billbot"
+version = "0.1.0"

Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "billbot"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

README.md

@@ -2,7 +2,7 @@
 
 _To :b:reserve and prötec_
 
-This will be a [Matrix](https://matrix.org) bot used to track
+This will be a [Matrix][matrix] bot used to track
 informal debts between some (small) group of individuals.
 
 its goals are (in order of importance):
@@ -42,3 +42,35 @@ below is an example of how this bot might work:
         > @user:host paid @other:host $NNN.MM
 - maybe state the remaining position?
         > @user:host now owes $other:host $X.YY
+
+
+## Development/Hacking
+
+this project is built with [cargo][cargo], the [Rust][rust] package manager. simply run:
+
+```sh
+$ cargo build
+$ ./target/debug/billbot
+```
+
+it can also be built with [nix][nix]:
+```sh
+$ nix build
+$ ./result/bin/billbot
+```
+
+a nix development environment (i.e. access to the correct toolchain) can be entered like so:
+```sh
+$ nix develop
+```
+
+after which ordinary cargo commands can be used:
+```sh
+nix-shell> cargo build
+nix-shell> ./target/debug/billbot
+```
+
+[matrix]: https://matrix.org
+[cargo]: https://doc.rust-lang.org/cargo
+[rust]: https://rust-lang.org
+[nix]: https://nixos.org

flake.lock

@@ -0,0 +1,42 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1678901627,
+        "narHash": "sha256-U02riOqrKKzwjsxc/400XnElV+UtPUQWpANPlyazjH0=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "93a2b84fc4b70d9e089d029deacc3583435c2ed6",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1680122840,
+        "narHash": "sha256-zCQ/9iFHzCW5JMYkkHMwgK1/1/kTMgCMHq4THPINpAU=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "a575c243c23e2851b78c00e9fa245232926ec32f",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "ref": "nixos-22.11",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,37 @@
+{
+  description = "Billbot matrix billshare bot";
+  inputs = {
+    nixpkgs.url = "nixpkgs/nixos-22.11";
+    flake-utils.url = github:numtide/flake-utils;
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    with flake-utils.lib; eachSystem allSystems (system:
+    let
+      pkgs = import nixpkgs {
+        inherit system;
+      };
+    in rec {
+      packages = {
+        # docs: <nixpkgs>/doc/languages-frameworks/rust.section.md
+        mx-billbot = pkgs.rustPlatform.buildRustPackage {
+          name = "mx-billbot";
+          src = self;
+          cargoLock.lockFile = ./Cargo.lock;
+          # enables debug builds, if we want: https://github.com/NixOS/nixpkgs/issues/60919.
+          hardeningDisable = [ "fortify" ];
+        };
+      };
+      defaultPackage = packages.mx-billbot;
+
+      devShells.default = with pkgs; mkShell {
+        # enables debug builds, if we want: https://github.com/NixOS/nixpkgs/issues/60919.
+        hardeningDisable = [ "fortify" ];
+
+        # Allow cargo to download crates.
+        SSL_CERT_FILE = "${cacert}/etc/ssl/certs/ca-bundle.crt";
+
+        nativeBuildInputs = [ cargo ];
+      };
+    });
+}

src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}