*: Migrate to Nix flakes, deprecate non-GHA CI

This simplifies the project setup and makes it easier to maintain the
CI pipeline.

.github/workflows/test.yml

@@ -12,24 +12,13 @@ on:
         type: boolean
 
 jobs:
-  nix-env:
-    name: Initialize Nix
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-
-      - name: Install Nix packages
-        uses: diamondburned/cache-install@main
-
   generate:
     name: Generate
-    needs: [nix-env]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-
-      - name: Install Nix packages
-        uses: diamondburned/cache-install@main
+      - uses: actions/checkout@v4
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
 
       - name: Generate
         run: |
@@ -46,46 +35,46 @@ jobs:
           fi
         env:
           GITHUB_REF: ${{ github.ref }}
+        shell: nix develop -c {0}
 
   build:
     name: Build
     runs-on: ubuntu-latest
     needs: [generate]
     steps:
-      - uses: actions/checkout@v2
-
-      - name: Install Nix packages
-        uses: diamondburned/cache-install@main
+      - uses: actions/checkout@v4
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
 
       - name: Build
-        run: go build ./...
+        run: go build -v ./...
+        shell: nix develop -c {0}
 
   unit-test:
     name: Unit Test
     runs-on: ubuntu-latest
     needs: [build]
     steps:
-      - uses: actions/checkout@v2
-
-      - name: Install Nix packages
-        uses: diamondburned/cache-install@main
+      - uses: actions/checkout@v4
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
 
       - name: Test
         run: go test $TEST_FLAGS ./...
         env:
           TEST_FLAGS: >-
             -v=${{ runner.debug && '1' || '0' }}
+        shell: nix develop -c {0}
 
   integration-test:
     name: Integration Test
     concurrency: integration-test
     runs-on: ubuntu-latest
     needs: [build]
     steps:
-      - uses: actions/checkout@v2
-
-      - name: Install Nix packages
-        uses: diamondburned/cache-install@main
+      - uses: actions/checkout@v4
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
 
       - name: Test
         run: |
@@ -99,6 +88,7 @@ jobs:
           GUILD_ID: ${{ secrets.GUILD_ID }}
           VOICE_ID: ${{ secrets.VOICE_ID }}
           BOT_TOKEN: ${{ secrets.BOT_TOKEN }}
+        shell: nix develop -c {0}
 
       - name: Upload coverage profile
         uses: actions/upload-artifact@v3

flake.nix

@@ -0,0 +1,31 @@
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+    }:
+
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          packages = with pkgs; [
+            go_1_22
+            gopls
+            go-tools
+
+            nixfmt-rfc-style
+          ];
+        };
+      }
+    );
+}