Use a nix flake with oxalica/rust-overlay instead of a shell.nix

flake.nix

@@ -0,0 +1,37 @@
+{
+  description = "tlater.net web server";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-20.09";
+    flake-utils.url = "github:numtide/flake-utils";
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs = {
+        flake-utils.follows = "flake-utils";
+        nixpkgs.follows = "nixpkgs";
+      };
+    };
+  };
+
+  outputs = { self, nixpkgs, flake-utils, rust-overlay }@inputs:
+    flake-utils.lib.simpleFlake {
+      inherit self nixpkgs;
+      name = "tlaternet";
+      preOverlays = [ rust-overlay.overlay ];
+
+      shell = { pkgs }:
+        let
+          rust_channel =
+            pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
+        in pkgs.mkShell {
+          nativeBuildInputs = with pkgs; [
+            (rust_channel.override {
+              extensions =
+                [ "rust-src" "rust-analysis" "rust-analyzer-preview" ];
+            })
+            pkgconfig
+          ];
+          buildInputs = with pkgs; [ openssl ];
+        };
+    };
+}