Nix flake and rustup toolchain format update (linera-io#1162)

* Add newer-format rust-toolchain with WASM support

The newer TOML `rust-toolchain.toml` format allows specifying more
things about the compiler.  Importantly, it allows us to require
support for particular targets, like `wasm32-unknown-unknown`.

We keep the legacy `rust-toolchain` file, in the legacy format, as it
is depended upon by CI.

rust-toolchain documentation:
https://rust-lang.github.io/rustup/overrides.html#the-toolchain-file

* Add Nix develop environment with Rust and WASM support

Reads the Rust toolchain specification from the rustup
`rust-toolchain.toml` file, and uses it to provide a development
environment for `linera-protocol` with required non-Rust dependencies
and standard development tools (`rustfmt`).

.envrc

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

.gitignore

@@ -17,3 +17,4 @@
 
 # VSCode
 .vscode
+/.direnv

flake.nix

@@ -0,0 +1,69 @@
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    systems.url = "github:nix-systems/default";
+    rust-overlay.url = "github:oxalica/rust-overlay";
+
+    # Dev tools
+    treefmt-nix.url = "github:numtide/treefmt-nix";
+  };
+
+  outputs = inputs: inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+    systems = import inputs.systems;
+    imports = [
+      inputs.treefmt-nix.flakeModule
+    ];
+    perSystem = { config, self', pkgs, lib, system, rust-overlay, ... }:
+      let
+        cargoToml = builtins.fromTOML (builtins.readFile ./Cargo.toml);
+        nonRustDeps = with pkgs; [
+          libclang.lib
+          libiconv
+          openssl
+          protobuf
+          pkg-config
+          nodejs
+        ];
+        rustToolchain = (pkgs.rust-bin.fromRustupToolchainFile
+          ./rust-toolchain.toml);
+        rustPlatform = pkgs.makeRustPlatform {
+          rustc = rustToolchain;
+          cargo = rustToolchain;
+        };
+      in {
+        _module.args.pkgs = import inputs.nixpkgs {
+          inherit system;
+          overlays = [ (import inputs.rust-overlay) ];
+        };
+
+        # Rust dev environment
+        devShells.default = pkgs.mkShell {
+          inputsFrom = [
+            config.treefmt.build.devShell
+          ];
+          shellHook = ''
+            # For rust-analyzer 'hover' tooltips to work.
+            export RUST_SRC_PATH=${rustToolchain.availableComponents.rust-src}
+            export LIBCLANG_PATH=${pkgs.libclang.lib}/lib
+            export PATH=$PWD/target/release:~/.cargo/bin:$PATH
+          '';
+          buildInputs = nonRustDeps;
+          nativeBuildInputs = with pkgs; [
+            rustToolchain
+            rust-analyzer
+          ];
+        };
+
+        # Add your auto-formatters here.
+        # cf. https://numtide.github.io/treefmt/
+        treefmt.config = {
+          projectRootFile = "flake.nix";
+          programs = {
+            nixpkgs-fmt.enable = true;
+            rustfmt.enable = true;
+          };
+        };
+      };
+  };
+}

linera-service/src/project.rs

@@ -167,11 +167,15 @@ impl Project {
     }
 
     fn create_rust_toolchain(project_root: &Path) -> Result<()> {
-        let toolchain_path = project_root.join("rust-toolchain");
         Self::write_string_to_file(
-            &toolchain_path,
+            &project_root.join("rust-toolchain"),
             include_str!("../template/rust-toolchain.template"),
-        )
+        )?;
+        Self::write_string_to_file(
+            &project_root.join("rust-toolchain.toml"),
+            include_str!("../template/rust-toolchain.toml.template"),
+        )?;
+        Ok(())
     }
 
     fn create_state_file(source_directory: &Path) -> Result<()> {

linera-service/template/rust-toolchain.toml.template

@@ -0,0 +1 @@
+../../rust-toolchain.toml

rust-toolchain.toml

@@ -0,0 +1,4 @@
+[toolchain]
+channel = "1.72.0"
+components = [ "rustfmt", "rustc-dev", "rust-src" ]
+targets = [ "wasm32-unknown-unknown" ]

shell.nix

@@ -0,0 +1 @@
+(builtins.getFlake ("git+file://" + toString ./.)).devShells.${builtins.currentSystem}.default