Chrono interoperability and Ops for Timestamp, update Nix and README

README.md

@@ -459,9 +459,21 @@ pub enum Gender {
 
 ## Nix
 
-The prost project maintains flakes support for local development. Once you have
-nix and nix flakes setup you can just run `nix develop` to get a shell
-configured with the required dependencies to compile the whole project.
+The prost project supports development using Nix flakes. Once you have Nix and flakes enabled, you can simply run:
+
+```
+nix develop
+```
+
+This will drop you into a shell with all dependencies configured to build the entire project.
+
+If you want to use the minimum supported Rust version as required by Tokio [see MSRV](#msrv), run:
+
+```
+nix develop .#rust_minimum_version
+```
+
+This ensures compatibility testing and development with the oldest supported toolchain version.
 
 ## Feature Flags
 - `std`: Enable integration with standard library. Disable this feature for `no_std` support. This feature is enabled by default.

flake.nix

@@ -4,17 +4,53 @@
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
     flake-utils.url = "github:numtide/flake-utils";
+    fenix.url = "github:nix-community/fenix";
+    rust_manifest = {
+      url = "https://static.rust-lang.org/dist/2023-08-03/channel-rust-1.71.1.toml";
+      flake = false;
+    };
   };
 
-  outputs = { self, nixpkgs, flake-utils }:
-    flake-utils.lib.eachDefaultSystem (system:
+  outputs =
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+      fenix,
+      rust_manifest,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
       let
         pkgs = import nixpkgs { inherit system; };
+        default_pkgs = with pkgs; [
+          protobuf
+          cmake
+          pkg-config
+          protobuf
+          curl
+          ninja
+        ];
       in
       {
-        devShells.default = pkgs.mkShell {
-          packages = with pkgs; [ cargo rustc ];
-          buildInputs = with pkgs; [ pkg-config protobuf curl cmake ninja ];
-        };
-      });
+        devShells.default =
+          let
+            rustpkgs = fenix.packages.${system}.stable.completeToolchain;
+          in
+          pkgs.mkShell {
+            packages = [
+              rustpkgs
+            ] ++ default_pkgs;
+          };
+        devShells."rust_minimum_version" =
+          let
+            rustpkgs = (fenix.packages.${system}.fromManifestFile rust_manifest).completeToolchain;
+          in
+          pkgs.mkShell {
+            packages = [
+              rustpkgs
+            ] ++ default_pkgs;
+          };
+      }
+    );
 }