nix: shell -> flake

Signed-off-by: Sumner Evans <me@sumnerevans.com>

.envrc

@@ -1,4 +1,8 @@
 if [[ $(uname -s) == "Linux" && $(uname --kernel-version | grep "NixOS") ]]; then
 	echo "The best OS (NixOS) has been detected. Using nice tools."
-	use nix
+	if ! has nix_direnv_version || ! nix_direnv_version 3.0.0; then
+		source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/3.0.0/direnvrc" "sha256-21TMnI2xWX7HkSTjFFri2UaohXVj854mgvWapWrxRXg="
+	fi
+
+	use flake
 fi

flake.nix

@@ -0,0 +1,33 @@
+{
+  description = "mautrix-signal development environment";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    (flake-utils.lib.eachDefaultSystem (system:
+      let pkgs = import nixpkgs { inherit system; };
+      in {
+        devShells.default = pkgs.mkShell {
+          LIBCLANG_PATH = "${pkgs.llvmPackages_11.libclang.lib}/lib";
+
+          buildInputs = with pkgs; [
+            clang
+            cmake
+            gnumake
+            protobuf
+            rust-cbindgen
+            rustup
+            olm
+
+            go_1_20
+            go-tools
+            gotools
+
+            pre-commit
+          ];
+        };
+      }));
+}