ci: enable use of the experimental installer

Author: getchoo

.github/actions/install-nix-action/action.yaml

@@ -4,6 +4,9 @@ inputs:
   dogfood:
     description: "Whether to use Nix installed from the latest artifact from master branch"
     required: true # Be explicit about the fact that we are using unreleased artifacts
+  experimental-installer:
+    description: "Whether to use the experimental installer to install Nix"
+    default: false
   extra_nix_config:
     description: "Gets appended to `/etc/nix/nix.conf` if passed."
   install_url:
@@ -37,14 +40,55 @@ runs:
 
         gh run download "$RUN_ID" --repo "$DOGFOOD_REPO" -n "$INSTALLER_ARTIFACT" -D "$INSTALLER_DOWNLOAD_DIR"
         echo "installer-path=file://$INSTALLER_DOWNLOAD_DIR" >> "$GITHUB_OUTPUT"
+        TARBALL_PATH="$(find "$INSTALLER_DOWNLOAD_DIR" -name 'nix*.tar.xz' -print | head -n 1)"
+        echo "tarball-path=file://$TARBALL_PATH" >> "$GITHUB_OUTPUT"
 
         echo "::notice ::Dogfooding Nix installer from master (https://github.com/$DOGFOOD_REPO/actions/runs/$RUN_ID)"
       env:
         GH_TOKEN: ${{ inputs.github_token }}
         DOGFOOD_REPO: "NixOS/nix"
+    - name: "Download experimental installer"
+      shell: bash
+      id: download-experimental-nix-installer
+      if: ${{ inputs.experimental-installer == 'true' }}
+      run: |
+        if [ "$RUNNER_OS" == "Linux" ]; then
+          INSTALLER_OS="linux"
+        elif [ "$RUNNER_OS" == "macOS" ]; then
+          INSTALLER_OS="darwin"
+        else
+          echo "::error ::Unsupported RUNNER_OS: $RUNNER_OS"
+        fi
+
+        if [ "$RUNNER_ARCH" == "X64" ]; then
+          INSTALLER_ARCH="x86_64"
+        elif [ "$RUNNER_ARCH" == "ARM64" ]; then
+          INSTALLER_ARCH="aarch64"
+        else
+          echo "::error ::Unsupported RUNNER_ARCH: $RUNNER_ARCH"
+        fi
+
+        EXPERIMENTAL_INSTALLER_ARTIFACT="nix-installer-$INSTALLER_ARCH-$INSTALLER_OS"
+        EXPERIMENTAL_INSTALLER_PATH="$GITHUB_WORKSPACE/$EXPERIMENTAL_INSTALLER_ARTIFACT"
+        # TODO: This uses the latest release. It should probably be pinned, or dogfood the experimental repo's default branch - similar to the above
+        gh release download -R "$EXPERIMENTAL_INSTALLER_REPO" -D "$EXPERIMENTAL_INSTALLER_PATH" -p "$EXPERIMENTAL_INSTALLER_ARTIFACT" -p "nix-installer.sh"
+
+        echo "installer-path=$EXPERIMENTAL_INSTALLER_PATH" >> "$GITHUB_OUTPUT"
+
+        echo "::notice Using experimental installer from $EXPERIMENTAL_INSTALLER_REPO (https://github.com/$EXPERIMENTAL_INSTALLER_REPO)"
+      env:
+        GH_TOKEN: ${{ inputs.github_token }}
+        EXPERIMENTAL_INSTALLER_REPO: "NixOS/experimental-nix-installer"
     - uses: cachix/install-nix-action@c134e4c9e34bac6cab09cf239815f9339aaaf84e # v31.5.1
+      if: ${{ inputs.experimental-installer != 'true' }}
       with:
         # Ternary operator in GHA: https://www.github.com/actions/runner/issues/409#issuecomment-752775072
         install_url: ${{ inputs.dogfood == 'true' && format('{0}/install', steps.download-nix-installer.outputs.installer-path) || inputs.install_url }}
         install_options: ${{ inputs.dogfood == 'true' && format('--tarball-url-prefix {0}', steps.download-nix-installer.outputs.installer-path) || '' }}
         extra_nix_config: ${{ inputs.extra_nix_config }}
+    - uses: DeterminateSystems/nix-installer-action@786fff0690178f1234e4e1fe9b536e94f5433196 # v20
+      if: ${{ inputs.experimental-installer == 'true' }}
+      with:
+        diagnostic-endpoint: ""
+        local-root: ${{ steps.download-experimental-nix-installer.outputs.installer-path }}
+        nix-package-url: ${{ inputs.dogfood && steps.download-nix-installer.outputs.tarball-path || '' }}

.github/workflows/ci.yml

@@ -11,6 +11,11 @@ on:
         required: false
         default: true
         type: boolean
+      experimental-installer:
+        description: 'Use the experimental installer'
+        required: false
+        default: false
+        type: boolean
 
 permissions: read-all
 
@@ -24,6 +29,7 @@ jobs:
     - uses: ./.github/actions/install-nix-action
       with:
         dogfood: ${{ github.event_name == 'workflow_dispatch' && inputs.dogfood || github.event_name != 'workflow_dispatch' }}
+        experimental-installer: ${{ github.event_name == 'workflow_dispatch' && inputs.experimental-installer || false }}
         extra_nix_config:
           experimental-features = nix-command flakes
         github_token: ${{ secrets.GITHUB_TOKEN }}
@@ -63,6 +69,7 @@ jobs:
       with:
         github_token: ${{ secrets.GITHUB_TOKEN }}
         dogfood: ${{ github.event_name == 'workflow_dispatch' && inputs.dogfood || github.event_name != 'workflow_dispatch' }}
+        experimental-installer: ${{ github.event_name == 'workflow_dispatch' && inputs.experimental-installer || false }}
         # The sandbox would otherwise be disabled by default on Darwin
         extra_nix_config: "sandbox = true"
     - uses: DeterminateSystems/magic-nix-cache-action@main
@@ -220,6 +227,7 @@ jobs:
       - uses: ./.github/actions/install-nix-action
         with:
           dogfood: ${{ github.event_name == 'workflow_dispatch' && inputs.dogfood || github.event_name != 'workflow_dispatch' }}
+          experimental-installer: ${{ github.event_name == 'workflow_dispatch' && inputs.experimental-installer || false }}
           extra_nix_config:
             experimental-features = nix-command flakes
           github_token: ${{ secrets.GITHUB_TOKEN }}
@@ -251,6 +259,7 @@ jobs:
       - uses: ./.github/actions/install-nix-action
         with:
           dogfood: ${{ github.event_name == 'workflow_dispatch' && inputs.dogfood || github.event_name != 'workflow_dispatch' }}
+          experimental-installer: ${{ github.event_name == 'workflow_dispatch' && inputs.experimental-installer || false }}
           extra_nix_config:
             experimental-features = nix-command flakes
           github_token: ${{ secrets.GITHUB_TOKEN }}
@@ -272,6 +281,7 @@ jobs:
       with:
         github_token: ${{ secrets.GITHUB_TOKEN }}
         dogfood: ${{ github.event_name == 'workflow_dispatch' && inputs.dogfood || github.event_name != 'workflow_dispatch' }}
+        experimental-installer: ${{ github.event_name == 'workflow_dispatch' && inputs.experimental-installer || false }}
         extra_nix_config: |
           experimental-features = flakes nix-command ca-derivations impure-derivations
           max-jobs = 1