chore(corp/rih): move frontend to a separate folder

Change-Id: Ic7467f459015c39c73f87c61a048319eaf1243be
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8714
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

corp/rih/frontend/default.nix

@@ -0,0 +1,52 @@
+{ lib, pkgs, ... }:
+
+let
+  wasmRust = pkgs.rust-bin.stable.latest.default.override {
+    targets = [ "wasm32-unknown-unknown" ];
+  };
+
+  cargoToml = with builtins; fromTOML (readFile ./Cargo.toml);
+
+  wasmBindgenMatch =
+    cargoToml.dependencies.wasm-bindgen == "= ${pkgs.wasm-bindgen-cli.version}";
+
+  assertWasmBindgen = assert (lib.assertMsg wasmBindgenMatch ''
+    Due to instability in the Rust WASM ecosystem, the trunk build
+    tool enforces that the Cargo-dependency version of `wasm-bindgen`
+    MUST match the version of the CLI supplied in the environment.
+
+    This can get out of sync when nixpkgs is updated. To resolve it,
+    wasm-bindgen must be bumped in the Cargo.toml file and cargo needs
+    to be run to resolve the dependencies.
+
+    Versions of `wasm-bindgen` in Cargo.toml:
+
+      Expected: '= ${pkgs.wasm-bindgen-cli.version}'
+      Actual:   '${cargoToml.dependencies.wasm-bindgen}'
+  ''); pkgs.wasm-bindgen-cli;
+
+  deps = with pkgs; [
+    binaryen
+    sass
+    wasmRust
+    trunk
+    assertWasmBindgen
+  ];
+
+in
+pkgs.rustPlatform.buildRustPackage rec {
+  pname = "rih-frontend";
+  version = "canon";
+  src = lib.cleanSource ./.;
+  cargoLock.lockFile = ./Cargo.lock;
+
+  buildPhase = ''
+    export PATH=${lib.makeBinPath deps}:$PATH
+    mkdir home
+    export HOME=$PWD/.home
+    env
+    trunk build --release -d $out
+  '';
+
+  dontInstall = true;
+}