feat: add manual dispatch to backport workflow (#5651)

Enables manual backport triggering for scenarios where labels are added
after PR merge.

Adds workflow_dispatch trigger to the backport workflow with support
for:
- Specifying PR number to backport post-merge
- Force rerun option to override duplicate detection  
- Proper handling of multi-version backport scenarios

Solves the issue where adding version labels (e.g., 1.27) after a PR is
already merged and backported (e.g., to 1.26) would not trigger
additional backports.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5651-feat-add-manual-dispatch-to-backport-workflow-2736d73d365081b6ba00c7a43c9ba06b)
by [Unito](https://www.unito.io)

.github/workflows/backport.yaml

@@ -4,10 +4,25 @@ on:
   pull_request_target:
     types: [closed, labeled]
     branches: [main]
+  workflow_dispatch:
+    inputs:
+      pr_number:
+        description: 'PR number to backport'
+        required: true
+        type: string
+      force_rerun:
+        description: 'Force rerun even if backports exist'
+        required: false
+        type: boolean
+        default: false
 
 jobs:
   backport:
-    if: github.event.pull_request.merged == true && contains(github.event.pull_request.labels.*.name, 'needs-backport')
+    if: >
+      (github.event_name == 'pull_request_target' && 
+       github.event.pull_request.merged == true && 
+       contains(github.event.pull_request.labels.*.name, 'needs-backport')) ||
+      github.event_name == 'workflow_dispatch'
     runs-on: ubuntu-latest
     permissions:
       contents: write
@@ -15,6 +30,35 @@ jobs:
       issues: write
 
     steps:
+      - name: Validate inputs for manual triggers
+        if: github.event_name == 'workflow_dispatch'
+        run: |
+          # Validate PR number format
+          if ! [[ "${{ inputs.pr_number }}" =~ ^[0-9]+$ ]]; then
+            echo "::error::Invalid PR number format. Must be a positive integer."
+            exit 1
+          fi
+          
+          # Validate PR exists and is merged
+          if ! gh pr view "${{ inputs.pr_number }}" --json merged >/dev/null 2>&1; then
+            echo "::error::PR #${{ inputs.pr_number }} not found or inaccessible."
+            exit 1
+          fi
+          
+          MERGED=$(gh pr view "${{ inputs.pr_number }}" --json merged --jq '.merged')
+          if [ "$MERGED" != "true" ]; then
+            echo "::error::PR #${{ inputs.pr_number }} is not merged. Only merged PRs can be backported."
+            exit 1
+          fi
+          
+          # Validate PR has needs-backport label
+          if ! gh pr view "${{ inputs.pr_number }}" --json labels --jq '.labels[].name' | grep -q "needs-backport"; then
+            echo "::error::PR #${{ inputs.pr_number }} does not have 'needs-backport' label."
+            exit 1
+          fi
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
       - name: Checkout repository
         uses: actions/checkout@v4
         with:
@@ -29,7 +73,7 @@ jobs:
         id: check-existing
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          PR_NUMBER: ${{ github.event.pull_request.number }}
+          PR_NUMBER: ${{ github.event_name == 'workflow_dispatch' && inputs.pr_number || github.event.pull_request.number }}
         run: |
           # Check for existing backport PRs for this PR number
           EXISTING_BACKPORTS=$(gh pr list --state all --search "backport-${PR_NUMBER}-to" --json title,headRefName,baseRefName | jq -r '.[].headRefName')
@@ -39,6 +83,13 @@ jobs:
             exit 0
           fi
           
+          # For manual triggers with force_rerun, proceed anyway
+          if [ "${{ github.event_name }}" = "workflow_dispatch" ] && [ "${{ inputs.force_rerun }}" = "true" ]; then
+            echo "skip=false" >> $GITHUB_OUTPUT
+            echo "::warning::Force rerun requested - existing backports will be updated"
+            exit 0
+          fi
+          
           echo "Found existing backport PRs:"
           echo "$EXISTING_BACKPORTS"
           echo "skip=true" >> $GITHUB_OUTPUT
@@ -50,8 +101,17 @@ jobs:
         run: |
           # Extract version labels (e.g., "1.24", "1.22")
           VERSIONS=""
-          LABELS='${{ toJSON(github.event.pull_request.labels) }}'
-          for label in $(echo "$LABELS" | jq -r '.[].name'); do
+          
+          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
+            # For manual triggers, get labels from the PR
+            LABELS=$(gh pr view ${{ inputs.pr_number }} --json labels | jq -r '.labels[].name')
+          else
+            # For automatic triggers, extract from PR event
+            LABELS='${{ toJSON(github.event.pull_request.labels) }}'
+            LABELS=$(echo "$LABELS" | jq -r '.[].name')
+          fi
+          
+          for label in $LABELS; do
             # Match version labels like "1.24" (major.minor only)
             if [[ "$label" =~ ^[0-9]+\.[0-9]+$ ]]; then
               # Validate the branch exists before adding to list
@@ -75,12 +135,20 @@ jobs:
         if: steps.check-existing.outputs.skip != 'true'
         id: backport
         env:
-          PR_NUMBER: ${{ github.event.pull_request.number }}
-          PR_TITLE: ${{ github.event.pull_request.title }}
-          MERGE_COMMIT: ${{ github.event.pull_request.merge_commit_sha }}
+          PR_NUMBER: ${{ github.event_name == 'workflow_dispatch' && inputs.pr_number || github.event.pull_request.number }}
         run: |
           FAILED=""
           SUCCESS=""
+          
+          # Get PR data for manual triggers
+          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
+            PR_DATA=$(gh pr view ${{ inputs.pr_number }} --json title,mergeCommit)
+            PR_TITLE=$(echo "$PR_DATA" | jq -r '.title')
+            MERGE_COMMIT=$(echo "$PR_DATA" | jq -r '.mergeCommit.oid')
+          else
+            PR_TITLE="${{ github.event.pull_request.title }}"
+            MERGE_COMMIT="${{ github.event.pull_request.merge_commit_sha }}"
+          fi
 
           for version in ${{ steps.versions.outputs.versions }}; do
             echo "::group::Backporting to core/${version}"
@@ -133,10 +201,18 @@ jobs:
         if: steps.check-existing.outputs.skip != 'true' && steps.backport.outputs.success
         env:
           GH_TOKEN: ${{ secrets.PR_GH_TOKEN }}
-          PR_TITLE: ${{ github.event.pull_request.title }}
-          PR_NUMBER: ${{ github.event.pull_request.number }}
-          PR_AUTHOR: ${{ github.event.pull_request.user.login }}
+          PR_NUMBER: ${{ github.event_name == 'workflow_dispatch' && inputs.pr_number || github.event.pull_request.number }}
         run: |
+          # Get PR data for manual triggers
+          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
+            PR_DATA=$(gh pr view ${{ inputs.pr_number }} --json title,author)
+            PR_TITLE=$(echo "$PR_DATA" | jq -r '.title')
+            PR_AUTHOR=$(echo "$PR_DATA" | jq -r '.author.login')
+          else
+            PR_TITLE="${{ github.event.pull_request.title }}"
+            PR_AUTHOR="${{ github.event.pull_request.user.login }}"
+          fi
+          
           for backport in ${{ steps.backport.outputs.success }}; do
             IFS=':' read -r version branch <<< "${backport}"
 
@@ -165,9 +241,16 @@ jobs:
         env:
           GH_TOKEN: ${{ github.token }}
         run: |
-          PR_NUMBER="${{ github.event.pull_request.number }}"
-          PR_AUTHOR="${{ github.event.pull_request.user.login }}"
-          MERGE_COMMIT="${{ github.event.pull_request.merge_commit_sha }}"
+          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
+            PR_DATA=$(gh pr view ${{ inputs.pr_number }} --json author,mergeCommit)
+            PR_NUMBER="${{ inputs.pr_number }}"
+            PR_AUTHOR=$(echo "$PR_DATA" | jq -r '.author.login')
+            MERGE_COMMIT=$(echo "$PR_DATA" | jq -r '.mergeCommit.oid')
+          else
+            PR_NUMBER="${{ github.event.pull_request.number }}"
+            PR_AUTHOR="${{ github.event.pull_request.user.login }}"
+            MERGE_COMMIT="${{ github.event.pull_request.merge_commit_sha }}"
+          fi
 
           for failure in ${{ steps.backport.outputs.failed }}; do
             IFS=':' read -r version reason conflicts <<< "${failure}"