Fix flakes example and add a test

idempotent installation

.github/workflows/test.yml

@@ -2,6 +2,8 @@ name: "install-nix-action test"
 on:
   pull_request:
   push:
+    branches:
+      - master
 
 jobs:
   simple-build:
@@ -56,3 +58,23 @@ jobs:
           sandbox = relaxed
     - run: cat /etc/nix/nix.conf
     - run: nix-build test.nix --arg noChroot true
+
+  flakes:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        # Nix Flakes doesn't work on shallow clones
+        fetch-depth: 0
+    - run: yarn install --frozen-lockfile
+    - run: yarn build
+    - name: Install Nix
+      uses: ./
+      with:
+        install_url: https://github.com/numtide/nix-flakes-installer/releases/download/nix-2.4pre20201221_9fab14a/install
+        extra_nix_config: |
+          experimental-features = nix-command flakes
+    - run: nix flake show github:NixOS/nixpkgs

README.md

@@ -6,7 +6,8 @@ Installs [Nix](https://nixos.org/nix/) on GitHub Actions for the supported platf
 
 By default it has no nixpkgs configured, you have to set `nix_path`
 by [picking a channel](https://status.nixos.org/)
-or [pin nixpkgs yourself](https://nix.dev/tutorials/towards-reproducibility-pinning-nixpkgs.html).
+or [pin nixpkgs yourself](https://nix.dev/reference/pinning-nixpkgs.html) 
+(see also [pinning tutorial](https://nix.dev/tutorials/towards-reproducibility-pinning-nixpkgs.html)).
 
 # Features
 
@@ -31,7 +32,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-    - uses: cachix/install-nix-action@v10
+    - uses: cachix/install-nix-action@v11
       with:
         nix_path: nixpkgs=channel:nixos-unstable
     - run: nix-build
@@ -43,7 +44,7 @@ with developers.
 
 ## Usage with Flakes
 
-```
+```yaml
 name: "Test"
 on:
   pull_request:
@@ -58,7 +59,7 @@ jobs:
           fetch-depth: 0
     - uses: cachix/install-nix-action@v11
       with:
-        install_url: https://github.com/numtide/nix-flakes-installer/releases/download/nix-3.0pre20200820_4d77513/install
+        install_url: https://github.com/numtide/nix-flakes-installer/releases/download/nix-3.0pre20201007_5257a25/install
         extra_nix_config: |
           experimental-features = nix-command flakes
     - run: nix-build
@@ -66,7 +67,7 @@ jobs:
 
 ## Inputs (specify using `with:`)
 
-- `install_url`: specify URL to install Nix from (useful for testing non-stable releases)
+- `install_url`: specify URL to install Nix from (useful for testing non-stable releases or pinning Nix for example https://releases.nixos.org/nix/nix-2.3.7/install)
 
 - `nix_path`: set `NIX_PATH` environment variable, for example `nixpkgs=channel:nixos-unstable`
 

lib/install-nix.sh

@@ -1,6 +1,11 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
+if type -p nix &>/dev/null ; then
+  echo "Aborting: Nix is already installed at $(type -p nix)"
+  exit
+fi
+
 # Configure Nix
 add_config() {
   echo "$1" | sudo tee -a /tmp/nix.conf >/dev/null
@@ -35,15 +40,15 @@ if [[ $OSTYPE =~ darwin ]]; then
 
   # macOS needs certificates hints
   cert_file=/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt
-  echo "::set-env name=NIX_SSL_CERT_FILE::$cert_file"
+  echo "NIX_SSL_CERT_FILE=$cert_file" >> $GITHUB_ENV
   export NIX_SSL_CERT_FILE=$cert_file
   sudo launchctl setenv NIX_SSL_CERT_FILE "$cert_file"
 fi
 
 # Set paths
-echo "::add-path::/nix/var/nix/profiles/per-user/$USER/profile/bin"
-echo "::add-path::/nix/var/nix/profiles/default/bin"
+echo "/nix/var/nix/profiles/per-user/$USER/profile/bin" >> $GITHUB_PATH
+echo "/nix/var/nix/profiles/default/bin" >> $GITHUB_PATH
 
 if [[ $INPUT_NIX_PATH != "" ]]; then
-  echo "::set-env name=NIX_PATH::${INPUT_NIX_PATH}"
+  echo "NIX_PATH=${INPUT_NIX_PATH}" >> $GITHUB_ENV
 fi

package.json

@@ -20,7 +20,7 @@
   "author": "Domen Kožar",
   "license": "ASL2",
   "dependencies": {
-    "@actions/core": "^1.1.0",
+    "@actions/core": "^1.2.6",
     "@actions/exec": "^1.0.1",
     "@actions/tool-cache": "^1.1.2"
   },

yarn.lock

@@ -2,10 +2,10 @@
 # yarn lockfile v1
 
 
-"@actions/core@^1.1.0":
-  version "1.1.1"
-  resolved "https://registry.yarnpkg.com/@actions/core/-/core-1.1.1.tgz#e08f3dbfe04721bb3d040f8fca2d6d7e1817b2e1"
-  integrity sha512-O5G6EmlzTVsng7VSpNtszIoQq6kOgMGNTFB/hmwKNNA4V71JyxImCIrL27vVHCt2Cb3ImkaCr6o27C2MV9Ylwg==
+"@actions/core@^1.1.0", "@actions/core@^1.2.6":
+  version "1.2.6"
+  resolved "https://registry.yarnpkg.com/@actions/core/-/core-1.2.6.tgz#a78d49f41a4def18e88ce47c2cac615d5694bf09"
+  integrity sha512-ZQYitnqiyBc3D+k7LsgSBmMDVkOVidaagDG7j3fOym77jNunWRuYx7VSHa9GNfFZh+zh61xsCjRj4JxMZlDqTA==
 
 "@actions/exec@^1.0.1":
   version "1.0.1"