Create preview PRs using labels

Benefits:

1. Ease of use - straight from the PR page
2. Workflow runs will show on the PR checks
3. Simplified logic in reusable workflow

.github/workflows/preview_on_auspice_us.yaml

@@ -0,0 +1,21 @@
+name: "Preview on auspice.us"
+on:
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - labeled
+
+  workflow_dispatch:
+
+jobs:
+  run:
+    # Run if PR has the label and is updated or is newly labeled with the label
+    if: |
+      (github.event.action != 'labeled' && contains(github.event.pull_request.labels.*.name, 'preview on auspice.us')) ||
+      (github.event.action == 'labeled' && github.event.label.name == 'preview on auspice.us')
+    uses: ./.github/workflows/preview_on_downstream_repo.yaml
+    secrets: inherit
+    with:
+      repository: nextstrain/auspice.us

.github/workflows/make_pr_for_downstream_repo.yaml → .github/workflows/preview_on_downstream_repo.yaml

@@ -1,4 +1,4 @@
-name: "Make PR for a repository which depends on Auspice"
+name: "Preview on downstream repo"
 on:
   workflow_call:
     inputs:
@@ -9,42 +9,19 @@ on:
         required: false
         type: string
         default: .
-jobs:
-  make-pr-on-downstream-repo:
-    # I don't see this being used for tags, so ensure it's only run on branches
-    # to make subsequent logic and wording easier.
-    if: github.ref_type == 'branch'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  run:
     runs-on: ubuntu-latest
 
     env:
       DESTINATION_REPO_DIR: repo
 
     steps:
-      # Outputs:
-      # - pr-number: The PR number from the branch name (exits if no PR exists).
-      # - auspice-sha: The GitHub-managed merge ref. Used for npm install.
-      #
-      # Note that $GITHUB_SHA shouldn't be used here because it refers to the
-      # branch HEAD which is not merged with the PR target branch. If the
-      # workflow trigger event was `pull_request` then it would refer to the
-      # merge ref¹, but we use `workflow_dispatch` to reduce the number of PRs.
-      #
-      # ¹ https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#pull_request
-      - name: Detect PR from branch
-        id: detect-pr
-        run: |
-          PR_NUMBER=$(gh pr view $GITHUB_REF_NAME --repo nextstrain/auspice --json 'number' --jq '.number') || true
-          if [[ -z $PR_NUMBER ]]; then
-            echo "ERROR: This branch is not associated with a PR in Auspice." >&2
-            exit 1
-          fi
-          MERGE_SHA=$(gh pr view $GITHUB_REF_NAME --repo nextstrain/auspice --json 'potentialMergeCommit' --jq '.potentialMergeCommit.oid')
-          echo "pr-number=$PR_NUMBER" >> $GITHUB_OUTPUT
-          echo "auspice-sha=$MERGE_SHA" >> $GITHUB_OUTPUT
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-
       - uses: actions/setup-node@v4
         with:
           node-version: '16'
@@ -61,7 +38,7 @@ jobs:
         working-directory: ${{ env.DESTINATION_REPO_DIR }}/${{ inputs.directory }}
         run: |
           npm ci
-          npm install nextstrain/auspice#${{ steps.detect-pr.outputs.auspice-sha }}
+          npm install nextstrain/auspice#${{ github.sha }}
           git add package.json package-lock.json
 
           git config user.name "nextstrain-bot"
@@ -73,17 +50,17 @@ jobs:
         working-directory: ${{ env.DESTINATION_REPO_DIR }}
         env:
           GITHUB_TOKEN: ${{ secrets.GH_TOKEN_NEXTSTRAIN_BOT_REPO }}
-          title: '[bot] [DO NOT MERGE] Test Auspice PR ${{ steps.detect-pr.outputs.pr-number }}'
+          title: '[bot] [DO NOT MERGE] Test Auspice PR ${{ github.event.number }}'
           body: |
-            This PR has been created to test this project running Auspice with changes from https://github.com/nextstrain/auspice/pull/${{ steps.detect-pr.outputs.pr-number }}.
+            This PR has been created to test this project running Auspice with changes from https://github.com/nextstrain/auspice/pull/${{ github.event.number }}.
 
             Note that Auspice has been installed with changes from both the PR's source and target branches.
             This will surface any issues that can arise from merging the PR in Auspice. To address these issues locally, update the source branch (e.g. with a git rebase).
 
             This message and corresponding commits were automatically created by a GitHub Action from [nextstrain/auspice](https://github.com/nextstrain/auspice).
           body_file: pr_body.txt
         run: |
-          branch="nextstrain-bot/test-auspice-pr/${{ steps.detect-pr.outputs.pr-number }}"
+          branch="nextstrain-bot/test-auspice-pr/${{ github.event.number }}"
           git switch -c "$branch"
           git push --force origin HEAD
           pr_url=$(gh pr list --head "$branch" --json url | jq -r '.[0].url')

.github/workflows/preview_on_nextstrain_org.yaml

@@ -0,0 +1,22 @@
+name: "Preview on nextstrain.org"
+on:
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - labeled
+
+  workflow_dispatch:
+
+jobs:
+  run:
+    # Run if PR has the label and is updated or is newly labeled with the label
+    if: |
+      (github.event.action != 'labeled' && contains(github.event.pull_request.labels.*.name, 'preview on nextstrain.org')) ||
+      (github.event.action == 'labeled' && github.event.label.name == 'preview on nextstrain.org')
+    uses: ./.github/workflows/preview_on_downstream_repo.yaml
+    secrets: inherit
+    with:
+      repository: nextstrain/nextstrain.org
+      directory: auspice-client

DEV_DOCS.md

@@ -100,12 +100,7 @@ A Heroku pipeline for this repository is connected to GitHub under the nextstrai
 
 #### Test on downstream repositories
 
-Additionally, a GitHub Actions workflow has been set up to generate PRs in downstream repositories that reflect the new changes in Auspice. To use it:
-
-1. Go to [the workflow page](https://github.com/nextstrain/auspice/actions/workflows/make_prs_for_other_repos.yaml).
-2. Select **Run workflow**.
-3. Pick the PR branch, select the downstream repositories you wish to test, and **Run workflow**.
-4. Wait for the workflow to finish running. The Auspice PR should show new reference links from the generated PRs.
+Additionally, a GitHub Actions workflow has been set up to generate PRs in downstream repositories that reflect the new changes in Auspice. To use it, add the label [preview on auspice.us](https://github.com/nextstrain/auspice/labels/preview%20on%20auspice.us) and/or [preview on nextstrain.org](https://github.com/nextstrain/auspice/labels/preview%20on%20nextstrain.org).
 
 ## git-lfs