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chore(repo): Add back-merge workflow for branch cascade
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‎.github/workflows/back_merge.yml‎

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name: Back-merge
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on:
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push:
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branches:
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- master
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- minor
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workflow_dispatch:
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concurrency:
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group: ${{ github.workflow }}-${{ github.ref }}
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cancel-in-progress: true
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jobs:
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resolve-branches:
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name: Resolve merge target
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runs-on: ubuntu-latest
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outputs:
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source: ${{ github.ref_name }}
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target: ${{ steps.target.outputs.branch }}
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steps:
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- name: Determine target branch
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id: target
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env:
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BRANCH: ${{ github.ref_name }}
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run: |
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if [ "$BRANCH" = "master" ]; then
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echo "branch=minor" >> "$GITHUB_OUTPUT"
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elif [ "$BRANCH" = "minor" ]; then
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echo "branch=major" >> "$GITHUB_OUTPUT"
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fi
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back-merge:
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name: 'Merge ${{ needs.resolve-branches.outputs.source }} → ${{ needs.resolve-branches.outputs.target }}'
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runs-on: ubuntu-latest
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needs: resolve-branches
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permissions:
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contents: write
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pull-requests: write
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steps:
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- name: Generate CI Bot Token
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id: app-token
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uses: actions/create-github-app-token@v2
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with:
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app-id: ${{ secrets.CI_BOT_APP_ID }}
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private-key: ${{ secrets.CI_BOT_APP_PRIVATE_KEY }}
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- name: Checkout target branch
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uses: actions/checkout@v4
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with:
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token: ${{ steps.app-token.outputs.token }}
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ref: ${{ needs.resolve-branches.outputs.target }}
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fetch-depth: 0
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- name: Get CI Bot user ID
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id: get-user-id
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env:
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GH_TOKEN: ${{ steps.app-token.outputs.token }}
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APP_SLUG: ${{ steps.app-token.outputs.app-slug }}
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run: |
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echo "user-id=$(gh api "/users/${APP_SLUG}%5Bbot%5D" --jq .id)" >> "$GITHUB_OUTPUT"
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- name: Attempt merge
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id: merge
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env:
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SOURCE: ${{ needs.resolve-branches.outputs.source }}
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TARGET: ${{ needs.resolve-branches.outputs.target }}
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APP_SLUG: ${{ steps.app-token.outputs.app-slug }}
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USER_ID: ${{ steps.get-user-id.outputs.user-id }}
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run: |
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git config user.name "${APP_SLUG}[bot]"
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git config user.email "${USER_ID}+${APP_SLUG}[bot]@users.noreply.github.com"
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git fetch origin "$SOURCE"
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if git merge-base --is-ancestor "origin/$SOURCE" HEAD; then
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echo "result=up-to-date" >> "$GITHUB_OUTPUT"
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echo "::notice::$TARGET is already up to date with $SOURCE"
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elif git merge "origin/$SOURCE" --no-edit; then
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echo "result=clean" >> "$GITHUB_OUTPUT"
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else
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git merge --abort
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echo "result=conflict" >> "$GITHUB_OUTPUT"
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fi
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# App token is used for the push (not GITHUB_TOKEN) so that
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# the push triggers downstream workflow runs for the cascade.
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- name: Push merge
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if: steps.merge.outputs.result == 'clean'
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env:
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TARGET: ${{ needs.resolve-branches.outputs.target }}
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run: git push origin "$TARGET"
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# GITHUB_TOKEN is sufficient for PR operations — they don't need
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# to trigger downstream workflows, and it avoids burning App token quota.
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- name: Check for existing back-merge PR
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if: steps.merge.outputs.result == 'conflict'
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id: check-pr
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env:
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GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
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SOURCE: ${{ needs.resolve-branches.outputs.source }}
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TARGET: ${{ needs.resolve-branches.outputs.target }}
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run: |
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EXISTING_PR=$(gh pr list \
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--base "$TARGET" \
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--head "$SOURCE" \
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--state open \
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--json number \
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--jq '.[0].number // empty')
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if [ -n "$EXISTING_PR" ]; then
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echo "found=true" >> "$GITHUB_OUTPUT"
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echo "pr_number=$EXISTING_PR" >> "$GITHUB_OUTPUT"
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echo "::notice::Found existing back-merge PR #$EXISTING_PR"
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else
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echo "found=false" >> "$GITHUB_OUTPUT"
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fi
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- name: Create back-merge PR
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if: steps.merge.outputs.result == 'conflict' && steps.check-pr.outputs.found != 'true'
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env:
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GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
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SOURCE: ${{ needs.resolve-branches.outputs.source }}
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TARGET: ${{ needs.resolve-branches.outputs.target }}
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run: |
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gh pr create \
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--base "$TARGET" \
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--head "$SOURCE" \
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--title "chore(repo): Back-merge $SOURCE into $TARGET (conflicts)" \
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--body "Automatic back-merge of \`$SOURCE\` into \`$TARGET\` failed due to merge conflicts.
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To resolve: check out \`$TARGET\`, merge \`$SOURCE\`, resolve the conflicts, and push to \`$TARGET\`.
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\`\`\`sh
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git checkout $TARGET
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git merge origin/$SOURCE
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# resolve conflicts
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git push origin $TARGET
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\`\`\`
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> Created automatically by the back-merge workflow."
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- name: Comment on existing back-merge PR
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if: steps.merge.outputs.result == 'conflict' && steps.check-pr.outputs.found == 'true'
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env:
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GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
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PR_NUMBER: ${{ steps.check-pr.outputs.pr_number }}
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SOURCE: ${{ needs.resolve-branches.outputs.source }}
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TARGET: ${{ needs.resolve-branches.outputs.target }}
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run: |
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gh pr comment "$PR_NUMBER" \
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--body "New conflicts detected during back-merge of \`$SOURCE\` into \`$TARGET\`. Please resolve the conflicts in this PR."

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