feat: support fully qualified flakes

Author: workflow

.github/workflows/test.yml

@@ -81,3 +81,27 @@ jobs:
           script: |
             echo The future is $FUTURE
             [[ -z "${ANSWER}" ]] && exit 1 || exit 0
+
+  test-flakes:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Nix
+        uses: cachix/install-nix-action@v18
+        with:
+          nix_path: nixpkgs=channel:release-21.05
+          extra_nix_config: |
+            access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+      - name: Test Basic Bash Shell with Local Flake
+        uses: ./
+        with:
+          flakes: .#hello
+          script: |
+            hello
+      - name: Test Bash Shell with Local and External Flakes
+        uses: ./
+        with:
+          flakes: .#hello,nixpkgs#docker
+          script: |
+            hello
+            command -v docker

README.md

@@ -46,6 +46,35 @@ For now, this action implicitly depends on having [Nix] installed and set up cor
 
 See also [cachix-action](https://github.com/cachix/cachix-action) for a simple binary cache setup to speed up your builds and share binaries with developers.
 
+## Use with Flakes
+Instead of specifying packages, you can use `flakes` to specify fully qualified flakes to be available in your script.
+This can be used for both local flakes in a `flake.nix` in your repo, as well as external flakes.
+
+```yaml
+name: "Test"
+on:
+  pull_request:
+  push:
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Nix
+        uses: cachix/install-nix-action@v18
+        with:
+          extra_nix_config: |
+            access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+      - uses: workflow/nix-shell-action@v3
+        with:
+          flakes: .#hello,nixpkgs#docker
+          script: |
+            # Runs hello from a local flake.nix
+            hello
+            # Uses docker from the nixpkgs registry (see https://raw.githubusercontent.com/NixOS/flake-registry/master/flake-registry.json)
+            command -v docker
+```
+
 ## Options `with: ...`
 
 - `interpreter`:  Interpreter to use in the nix shell shebang, defaults to `bash`. (This is passed to `nix run -c`, used to be `-i` in a nix shell shebang)

dist/index.js

@@ -0,0 +1,11 @@
+{
+  description = "A very basic flake";
+
+  outputs = { self, nixpkgs }: {
+
+    packages.x86_64-linux.hello = nixpkgs.legacyPackages.x86_64-linux.hello;
+
+    packages.x86_64-linux.default = self.packages.x86_64-linux.hello;
+
+  };
+}

dist/index.js.map

@@ -6,6 +6,7 @@ function run(): void {
   try {
     const interpreter: string = core.getInput('interpreter')
     const packages: string = core.getInput('packages')
+    const flakes: string = core.getInput('flakes')
     const script: string = core.getInput('script')
 
     const nixWrapperPath = `${__dirname}/wrapper.sh`
@@ -16,10 +17,12 @@ function run(): void {
       .map(pkg => `nixpkgs.${pkg.trim()}`)
       .join(' ')
 
-    const flakeWrappedPackages = packages
-      .split(',')
-      .map(pkg => `nixpkgs#${pkg.trim()}`)
-      .join(' ')
+    const flakeWrappedPackages =
+      flakes.split(',').join(' ') ||
+      packages
+        .split(',')
+        .map(pkg => `nixpkgs#${pkg.trim()}`)
+        .join(' ')
 
     const nixWrapper = `
 set -euo pipefail
@@ -40,7 +43,7 @@ then
   nix run ${wrappedPackages} -c ${interpreter} ${scriptPath}
 else
   # nix 2.4 and later: nix shell
-  nix --experimental-features 'nix-command flakes' shell ${flakeWrappedPackages} -c ${interpreter} ${scriptPath} 
+  nix --experimental-features 'nix-command flakes' shell ${flakeWrappedPackages} -c ${interpreter} ${scriptPath}
 fi
       `