Expose option to configure branch for PR (#36)

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/83658b28fe638a170a19b8933aa008b30640fbd1' (2022-05-26)
  → 'github:nixos/nixpkgs/e0169d7a9d324afebf5679551407756c77af8930' (2022-06-08)

.github/workflows/ci.yml

@@ -0,0 +1,17 @@
+name: CI
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  shellcheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+      - name: Install Nix
+        uses: cachix/install-nix-action@v16
+      - name: Shellcheck
+        run: nix-shell --run 'shellcheck $(find . -type f -name "*.sh" -executable)'

.github/workflows/update.yml

@@ -0,0 +1,19 @@
+name: update-flake-lock
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '0 0 * * 0'
+
+jobs:
+  lockfile:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+      - name: Install Nix
+        uses: cachix/install-nix-action@v16
+        with:
+          extra_nix_config: |
+            access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+      - name: Update flake.lock
+        uses: ./.

README.md

@@ -65,6 +65,65 @@ jobs:
           inputs: input1 input2 input3
 ```
 
+## Example that prints the number of the created PR
+
+```yaml
+name: update-flake-lock
+on:
+  workflow_dispatch: # allows manual triggering
+  schedule:
+    - cron: '0 0 * * 0' # runs weekly on Sunday at 00:00
+
+jobs:
+  lockfile:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+      - name: Install Nix
+        uses: cachix/install-nix-action@v16
+        with:
+          extra_nix_config: |
+            access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+      - name: Update flake.lock
+        id: update
+        uses: DeterminateSystems/update-flake-lock@vX
+        with:
+          inputs: input1 input2 input3
+      - name: Print PR number
+        run: echo Pull request number is ${{ steps.update.outputs.pull-request-number }}.
+```
+
+## Example that doesn't run on PRs
+
+If you were to run this action as a part of your CI workflow, you may want to prevent it from running against Pull Requests.
+
+```yaml
+name: update-flake-lock
+on:
+  workflow_dispatch: # allows manual triggering
+  pull_request: # triggers on every Pull Request
+  schedule:
+    - cron: '0 0 * * 0' # runs weekly on Sunday at 00:00
+
+jobs:
+  lockfile:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+      - name: Install Nix
+        uses: cachix/install-nix-action@v16
+        with:
+          extra_nix_config: |
+            access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+      - name: Update flake.lock
+        if: ${{ github.event_name != 'pull_request' }}
+        uses: DeterminateSystems/update-flake-lock@vX
+        with:
+          inputs: input1 input2 input3
+```
+
 ## Running GitHub Actions CI
 
 GitHub Actions will not run workflows when a branch is pushed by or a PR is opened by a GitHub Action. There are two ways to have GitHub Actions CI run on a PR submitted by this action.

action.yml

@@ -13,6 +13,10 @@ inputs:
     description: 'The message provided with the commit'
     required: false
     default: "flake.lock: Update"
+  branch:
+    description: 'The branch of the PR to be created'
+    required: false
+    default: "update_flake_lock_action"
   pr-title:
     description: 'The title of the PR to be created'
     required: false
@@ -21,25 +25,22 @@ inputs:
     description: 'A comma or newline separated list of labels to set on the Pull Request to be created'
     required: false
     default: ''
+outputs:
+  pull-request-number:
+    description: 'The number of the opened pull request'
+    value: ${{ steps.create-pr.outputs.pull-request-number }}
 runs:
   using: "composite"
   steps:
-    - run: |
-        if [[ -n '${{ inputs.inputs }}' ]]; then
-          inputs=()
-          for input in ${{ inputs.inputs }}; do
-            inputs+=("--update-input" "$input")
-          done
-          nix flake lock "${inputs[@]}" --commit-lock-file --commit-lockfile-summary "${{ inputs.commit-msg }}"
-        else
-          nix flake update --commit-lock-file --commit-lockfile-summary "${{ inputs.commit-msg }}"
-        fi
+    - run: $GITHUB_ACTION_PATH/update-flake-lock.sh
       shell: bash
       env:
         GIT_AUTHOR_NAME: github-actions[bot]
         GIT_AUTHOR_EMAIL: <github-actions[bot]@users.noreply.github.com>
         GIT_COMMITTER_NAME: github-actions[bot]
         GIT_COMMITTER_EMAIL: <github-actions[bot]@users.noreply.github.com>
+        TARGETS: ${{ inputs.inputs }}
+        COMMIT_MSG: ${{ inputs.commit-msg }}
     - run: |
         content="$(git log --format=%b -n 1)"
         content="${content//'%'/'%25'}"
@@ -49,9 +50,10 @@ runs:
       shell: bash
       id: commit_message
     - name: Create PR
+      id: create-pr
       uses: peter-evans/create-pull-request@v3
       with:
-        branch: update_flake_lock_action
+        branch: ${{ inputs.branch }}
         delete-branch: true
         title: ${{ inputs.pr-title }}
         token: ${{ inputs.token }}

flake.lock

@@ -2,16 +2,16 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1638263381,
-        "narHash": "sha256-1rZDxTw74ETuJEjwPfpMgY0sfx8Cv1tRNt3gibol574=",
+        "lastModified": 1654682581,
+        "narHash": "sha256-Jb1PQCwKgwdNAp907eR5zPzuxV+kRroA3UIxUxCMJ9s=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "7b031d0d99e8cdaf0b70457c0cb33f16c0c958bb",
+        "rev": "e0169d7a9d324afebf5679551407756c77af8930",
         "type": "github"
       },
       "original": {
         "owner": "nixos",
-        "ref": "nixos-unstable-small",
+        "ref": "nixos-unstable",
         "repo": "nixpkgs",
         "type": "github"
       }

update-flake-lock.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [[ -n "$TARGETS" ]]; then
+    inputs=()
+    for input in $TARGETS; do
+        inputs+=("--update-input" "$input")
+    done
+    nix flake lock "${inputs[@]}" --commit-lock-file --commit-lockfile-summary "$COMMIT_MSG"
+else
+    nix flake update --commit-lock-file --commit-lockfile-summary "$COMMIT_MSG"
+fi