Add pre-commit infrastructure (#401)

Does not include any hooks yet.

.github/workflows/pre-commit.yaml

@@ -0,0 +1,27 @@
+---
+name: Check pre-commit hooks
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
+
+permissions: read-all
+
+jobs:
+  pre-commit-checks:
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Checkout
+        uses: >- # v3.5.3
+          actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9
+      - name: Install Nix
+        uses: >- #v7
+          DeterminateSystems/nix-installer-action@5620eb4af6b562c53e4d4628c0b6e4f9d9ae8612
+      - name: Cache Nix derivations
+        uses: >- # Custom commit, last pinned at 2023-11-17.
+          DeterminateSystems/magic-nix-cache-action@a04e6275a6bea232cd04fc6f3cbf20d4cb02a3e1
+      - name: Run pre-commit hooks
+        run: nix flake check

.gitignore

@@ -9,3 +9,4 @@ __pycache__
 .devenv/
 .direnv/
 .DS_Store
+.pre-commit-config.yaml

flake.nix

@@ -3,11 +3,13 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    pre-commit-hooks.url = "github:cachix/pre-commit-hooks.nix";
   };
 
   outputs = inputs@{ nixpkgs, flake-parts, ... }:
     flake-parts.lib.mkFlake { inherit inputs; } {
       systems = [ "x86_64-linux" ];
+      imports = [ inputs.pre-commit-hooks.flakeModule ];
       perSystem = { config, self', inputs', pkgs, system, ... }:
         let
           # Link OpenSSL statically into the openssl-sys crate.
@@ -19,17 +21,25 @@
             bazel = pkgs.bazel;
             writeShellScriptBin = pkgs.writeShellScriptBin;
           };
+
+          hooks = import ./tools/pre-commit-hooks.nix { inherit pkgs; };
         in
         {
+          pre-commit.settings = { inherit hooks; };
           devShells.default = pkgs.mkShell {
             nativeBuildInputs = [
               # Development tooling goes here.
               pkgs.cargo
               pkgs.rustc
+              pkgs.pre-commit
               openssl_static # Required explicitly for cargo test support.
               bazel
             ];
             shellHook = ''
+              # Generate the .pre-commit-config.yaml symlink when entering the
+              # development shell.
+              ${config.pre-commit.installationScript}
+
               # The Bazel and Cargo builds in nix require a Clang toolchain.
               # TODO(aaronmondal): The Bazel build currently uses the
               #                    irreproducible host C++ toolchain. Provide

tools/pre-commit-hooks.nix

@@ -0,0 +1,4 @@
+{ pkgs, ... }:
+{
+  # TODO(aaronmondal): Add hooks here.
+}