Merge pull request #951 from vancluever/vancluever-nix-action

nix: add GitHub Actions workflow

.github/workflows/nix.yml

@@ -0,0 +1,30 @@
+on: [push, pull_request]
+name: Nix
+jobs:
+  check-zig-cache-hash:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Setup Nix
+        uses: cachix/install-nix-action@v23
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      - name: Check Zig cache hash
+        run: nix develop -c ./nix/build-support/check-zig-cache-hash.sh
+  build:
+    needs: check-zig-cache-hash
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Setup Nix
+        uses: cachix/install-nix-action@v23
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      - name: Setup Nix cache
+        uses: DeterminateSystems/magic-nix-cache-action@main
+        with:
+          diagnostic-endpoint: "" # disable telemetry
+      - name: Run build
+        run: nix build .

README.md

@@ -469,3 +469,70 @@ prettier --write .
 ```
 
 Make sure your Prettier version matches the version of in [devshell.nix](https://github.com/mitchellh/ghostty/blob/main/nix/devshell.nix).
+
+### Nix Package
+
+> [!WARNING]
+> The Nix package currently depends on versions of LLVM and Zig that are
+> currently not in cache.nixos.org and will be built from source. This can take
+> a very long time, especially in situations where CPU is at a premium. Most
+> people should follow the instructions in [Developing
+> Ghostty](#developing-ghostty) instead.
+
+There is a functional Nix package that can be used in the `flake.nix` file
+(`packages.ghostty`). It can be used in NixOS configurations and otherwise
+built off of (however, please heed the above warning).
+
+Below is a sample on how to add it to a NixOS overlay:
+
+```nix
+{
+  inputs = {
+    nixpkgs.url = github:NixOS/nixpkgs/nixos-unstable;
+
+    # NOTE: This will require your git SSH access to the repo
+    ghostty = {
+      url = git+ssh://git@github.com/mitchellh/ghostty;
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs = { nixpkgs, ghostty, ... }: {
+    nixosConfigurations.nixos = nixpkgs.lib.nixosSystem {
+      modules = [
+        {
+          nixpkgs.overlays = [
+            (final: prev: {
+              ghostty = ghostty.packages.${prev.system}.ghostty;
+            })
+          ];
+        }
+
+        # Other modules here...
+      ];
+    };
+  };
+}
+```
+
+You can also test the build of the nix package at any time by running `nix build .`
+
+#### Updating the Zig Cache Fixed-Output Derivation Hash
+
+The Nix package depends on a [fixed-output
+derivation](https://nixos.org/manual/nix/stable/language/advanced-attributes.html#adv-attr-outputHash)
+that manages the Zig package cache. This allows the package to be built in the
+Nix sandbox.
+
+Occasionally (usually when `build.zig.zon` is updated), the hash that
+identifies the cache will need to be updated. There are jobs that monitor the
+hash in CI, and builds will fail if it drifts.
+
+To update it, you can run the following in the repository root:
+
+```
+./nix/build-support/check-zig-cache-hash.sh --update
+```
+
+This will write out the `nix/zig_cache_hash.nix` file with the updated hash
+that can then be committed and pushed to fix the builds.

nix/build-support/check-zig-cache-hash.sh

@@ -0,0 +1,60 @@
+#!/usr/bin/env bash
+
+# Nothing in this script should fail.
+set -e
+
+CACHE_HASH_FILE="$(realpath "$(dirname "$0")/../zig_cache_hash.nix")"
+
+help() {
+  echo ""
+  echo "To fix, please (manually) re-run the script from the repository root,"
+  echo "commit, and push the update:"
+  echo ""
+  echo "    ./nix/build-support/check-zig-cache-hash.sh --update"
+  echo "    git add nix/zig_cache_hash.nix"
+  echo "    git commit -m \"nix: update Zig cache hash\""
+  echo "    git push"
+  echo ""
+}
+
+if [ -f "${CACHE_HASH_FILE}" ]; then
+  OLD_CACHE_HASH="$(nix eval --raw --file "${CACHE_HASH_FILE}")"
+elif [ "$1" != "--update" ]; then
+  echo -e "\nERROR: Zig cache hash file missing."
+  help
+  exit 1
+fi
+
+TMP_CACHE_DIR="$(mktemp --directory --suffix nix-zig-cache)"
+# This is not 100% necessary in CI but is helpful when running locally to keep
+# a local workstation clean.
+trap 'rm -rf "${TMP_CACHE_DIR}"' EXIT
+
+# Run Zig and download the cache to the temporary directory.
+zig build --fetch --global-cache-dir "${TMP_CACHE_DIR}"
+
+# Now, calculate the hash.
+ZIG_CACHE_HASH="sha256-$(nix-hash --type sha256 --to-base64 "$(nix-hash --type sha256 "${TMP_CACHE_DIR}")")"
+
+if [ "${OLD_CACHE_HASH}" == "${ZIG_CACHE_HASH}" ]; then
+  echo -e "\nOK: Zig cache store hash unchanged."
+  exit 0
+elif [ "$1" != "--update" ]; then
+  echo -e "\nERROR: The Zig cache store hash has updated."
+  echo ""
+  echo "    * Old hash: ${OLD_CACHE_HASH}"
+  echo "    * New hash: ${ZIG_CACHE_HASH}"
+  help
+  exit 1
+else
+  echo -e "\nNew Zig cache store hash: ${ZIG_CACHE_HASH}"
+fi
+
+# Write out the cache file
+cat > "${CACHE_HASH_FILE}" <<EOS
+# This file is auto-generated! check build-support/check-zig-cache-hash.sh for
+# more details.
+"${ZIG_CACHE_HASH}"
+EOS
+
+echo -e "\nOK: Wrote new hash to file: ${CACHE_HASH_FILE}"

nix/package.nix

@@ -57,7 +57,7 @@ let
   # (It's also possible that you might see a hash mismatch - without the
   # network errors - if you don't have a previous instance of the cache
   # derivation in your store already. If so, just update the value as above.)
-  zigCacheHash = "sha256-/6XhZq5NYWbHhg0yQ9iT/6oGewsurIpeGNJyNT+E6CQ=";
+  zigCacheHash = import ./zig_cache_hash.nix;
 
   zigCache = src: stdenv.mkDerivation {
     inherit src;

nix/zig_cache_hash.nix

@@ -0,0 +1,3 @@
+# This file is auto-generated! check build-support/write-zig-cache-hash.sh for
+# more details.
+"sha256-/6XhZq5NYWbHhg0yQ9iT/6oGewsurIpeGNJyNT+E6CQ="