ci: Automation for backporting PRs

Signed-off-by: Tyler Smalley <tyler@tailscale.com>

.backportrc.json

@@ -0,0 +1,14 @@
+{
+  "repoOwner": "tailscale-dev",
+  "repoName": "vscode-tailscale",
+
+  "targetBranchChoices": ["release-branch/v0.4"],
+
+  "branchLabelMapping": {
+    "^v(\\d+).(\\d+).\\d+$": "release-branch/v$1.$2"
+  },
+
+  "fork": false,
+
+  "targetPRLabels": ["backport"]
+}

.github/workflows/backport.yml

@@ -0,0 +1,31 @@
+on:
+  pull_request_target:
+    branches: ['main']
+    types: ['labeled', 'closed']
+
+jobs:
+  backport:
+    name: Backport PR
+    runs-on: ubuntu-latest
+    if: |
+      github.event.pull_request.merged == true
+      && contains(github.event.pull_request.labels.*.name, 'auto-backport')
+      && (
+        (github.event.action == 'labeled' && github.event.label.name == 'auto-backport')
+        || (github.event.action == 'closed')
+      )
+    steps:
+      - name: Backport Action
+        uses: sqren/backport-github-action@e325a2d70df7264afa24c92b1d5feb2278ff63af
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          auto_backport_label_prefix: auto-backport-to-
+          add_original_reviewers: true
+
+      - name: Info log
+        if: ${{ success() }}
+        run: cat ~/.backport/backport.info.log
+
+      - name: Debug log
+        if: ${{ failure() }}
+        run: cat ~/.backport/backport.debug.log

package.json

@@ -226,6 +226,7 @@
     "@vscode/vsce": "^2.18.0",
     "@vscode/webview-ui-toolkit": "^1.2.2",
     "autoprefixer": "^10.4.14",
+    "backport": "^8.9.7",
     "bufferutil": "^4.0.7",
     "css-loader": "^6.7.3",
     "eslint": "^8.34.0",