Fix branchLabelMapping precedence for main override in .backportrc.json

[edsavage]

Summary

The backport tool (sorenlouv/backport-github-action) applies the first matching branchLabelMapping entry. The minor-freeze automation appended the specific main override after the generic rule, so on main we ended up with:

"branchLabelMapping": {
  "^v(\\d+).(\\d+).\\d+(?:-(?:alpha|beta|rc)\\d+)?$": "$1.$2",
  "^v9.6.0$": "main"
}

The generic ^vX.Y.Z$ rule matched v9.6.0 first and resolved it to 9.6, a branch that does not exist. This is why merging #3071 (labeled v9.6.0) triggered a failing backport attempt to a non-existent 9.6 branch.

Changes

• .backportrc.json: reorder so ^v9.6.0$ -> main precedes the generic ^vX.Y.Z$ -> X.Y rule.
• dev-tools/update_backportrc.py: rebuild branchLabelMapping with the main-only override emitted first, and treat a pure reorder as a change so future minor freezes produce the correct order. Stale main overrides (e.g. ^v9.5.0$) are still removed.
• dev-tools/unittest/test_update_backportrc.py: new tests asserting the main override is emitted first, stale overrides are dropped, reorders are detected as changes, and the operation is idempotent when already correct.

Test plan

• python3 -m pytest dev-tools/unittest/test_update_backportrc.py -q passes
• Running update_backportrc.py against the fixed .backportrc.json is idempotent (reports "already configured", no diff)
• Next PR labeled v9.6.0 should map to main (or be skipped where appropriate) and not attempt a 9.6 backport

Related

• Follows up on the spurious/failing backports observed on [ML] Bump version to 9.6.0 (minor freeze) #3068 ([9.5] [ML] Bump version to 9.6.0 (minor freeze) (#3068) #3069) and Fix main-snapshot DRA alias lookup in minor-freeze wait #3071.
• Complements the no-backport guard added in [ML] Skip backport for minor-freeze version bump PRs #3070; this PR fixes the mapping so version-labeled PRs resolve to the correct branch.

Made with Cursor

[prodsecmachine]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues

💻 Catch issues earlier using the plugins for VS Code, JetBrains IDEs, Visual Studio, and Eclipse.

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)

[Copilot]

Pull request overview

This PR fixes the ordering semantics of Backport’s branchLabelMapping so that the main-only version override (e.g. ^v9.6.0$ -> main) is evaluated before the generic ^vX.Y.Z$ -> X.Y rule, preventing backport attempts to non-existent release branches (e.g. 9.6).

Changes:

• Reorders .backportrc.json so the v9.6.0 -> main mapping precedes the generic mapping.
• Updates dev-tools/update_backportrc.py to rebuild branchLabelMapping with the main override first and to detect pure reorders as changes.
• Adds pytest coverage ensuring main override precedence, stale override removal, reorder detection, and idempotency.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
dev-tools/update_backportrc.py	Rebuilds branchLabelMapping with the main override first and detects reorder-only changes.
dev-tools/unittest/test_update_backportrc.py	Adds regression tests for mapping order, stale override removal, reorder detection, and idempotency.
.backportrc.json	Reorders mapping entries so the main override is matched before the generic rule.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.