Fix Chopsticks runtime-upgrade test panic (InvalidNumberOfDescendants)

[arturgontijo]

What does it do?

Fixes the chopsticks-upgrade-test CI job (moonbeam / moonriver / moonbase) which
was failing during block production after the runtime upgrade with:

Runtime has aborted: "panicked at .../cumulus/pallets/parachain-system/src/lib.rs:623:
Unable to verify provided relay parent descendants.
expected_rp_descendants_num: 1 error: InvalidNumberOfDescendants { expected: 2, received: 0 }"

Root cause. The upgraded runtime wires parachain-system's RelayParentOffset
to pallet_async_backing, whose RelayParentOffset storage value now defaults to 1.
With the offset > 0, set_validation_data verifies that the inherent carries
RelayParentOffset + 1 = 2 relay-parent descendant headers. Chopsticks mocks the
relay chain and builds the setValidationData inherent with 0 descendants, so every
block built under the new runtime panics. beforeAll passes because those blocks still
run under the old (live) runtime, which does not enforce the check; the first block
built under the new runtime (C01T1) is the one that fails.

Fix. After the upgrade is applied, force AsyncBacking::RelayParentOffset to 0
in the forked chain (set_validation_data skips the descendant check when the offset
is 0). This is a Chopsticks-only accommodation; the real network is unaffected
because real collators source the descendant headers from the live relay chain.

This also reverts the earlier, ineffective workarounds for the same panic:

• Removed the block-production retry helpers in test-upgrade-chain.ts (added in Reduce CI runner cost and make CI less flaky (pass 2) #3757).
  The panic is deterministic, so retrying never helped — it just exhausted attempts and
  then failed the height assertion.
• Removed test/scripts/select-chopsticks-fork-block.ts, the CI step that ran it, and the
  block: ${env.CHOPSTICKS_BLOCK} config entries (added in Make Chopsticks runtime upgrade tests less flaky in CI #3765). Fork-block selection
  is irrelevant here: the failing inherent is fabricated fresh for each new block,
  independent of the fork block. Chopsticks now forks from the latest finalized block again.

What important points should reviewers know?

• The fix lives entirely in the Chopsticks test setup; no runtime/node code changes.
• disableRelayParentOffset writes the raw u32 value 0x00000000. Passing a falsy
  value (e.g. 0) to moonwall's setStorage would delete the key and fall back to the
  default of 1, so the explicit little-endian hex is intentional.
• The override is applied after dev_newBlock({ count: 3 }) so the new runtime's metadata
  (which contains asyncBacking.relayParentOffset) is already active when the storage is set.
• Applies to all three networks (moonbeam, moonriver, moonbase), which all map
  RelayParentOffset = AsyncBacking.

Is there something left for follow-up PRs?

• If/when Chopsticks gains the ability to synthesize relay-parent descendant headers,
  the offset override could be dropped to exercise the feature end-to-end in the fork test.

What alternative implementations were considered?

• Upgrading Chopsticks (1.2.8 → ≥1.3.1/1.4.x): the 1.3.1 fix only corrects descendant
  state roots when descendants are already populated; it does not synthesize the missing
  descendants, so it would not resolve InvalidNumberOfDescendants { received: 0 }.
• Selecting a fork block with ≥2 descendants: not possible — production Moonbeam blocks
  currently carry 0 descendants, and descendants of the fork block don't propagate into the
  freshly built inherents anyway.

Are there relevant PRs or issues in other repositories (Substrate, Polkadot, Frontier, Cumulus)?

• polkadot-sdk cumulus-pallet-parachain-system RelayParentOffset / relay-parent descendant
  verification.
• Update relayParentDescendants state roots in old setValidationData AcalaNetwork/chopsticks#1017 (descendant state-root handling) — related but does not cover the
  empty-descendants case hit here.

What value does it bring to the blockchain users?

• Restores the Chopsticks runtime-upgrade test as a reliable pre-release safety net, ensuring
  runtime upgrades that change relay-parent-offset behavior are validated in CI before shipping.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 9aec9047-702b-49c8-a948-de569c7076a0

📥 Commits

Reviewing files that changed from the base of the PR and between 77065ab and eb3e274.

📒 Files selected for processing (6)

• .github/workflows/build.yml
• test/configs/alphanet.yml
• test/configs/moonbeam.yml
• test/configs/moonriver.yml
• test/scripts/select-chopsticks-fork-block.ts
• test/suites/chopsticks/test-upgrade-chain.ts

💤 Files with no reviewable changes (5)

• test/configs/moonriver.yml
• test/configs/moonbeam.yml
• .github/workflows/build.yml
• test/configs/alphanet.yml
• test/scripts/select-chopsticks-fork-block.ts

---

📝 Walkthrough

Walkthrough

The fork-block selection script gains an anchored relay-chain state proof requirement enforced via blake2AsHex hashing and proof validation. Test configurations remove environment-based block selection, the CI workflow replaces the fork-block selection step with a direct install step, and the test suite adds a helper to disable relay-parent offset after runtime upgrade, switching from retry-based to direct block creation.

Changes

Anchored proof gate and test suite adaptation

Layer / File(s)	Summary
Config and workflow cleanup test/configs/alphanet.yml, test/configs/moonbeam.yml, test/configs/moonriver.yml, .github/workflows/build.yml	Removes block: ${env.CHOPSTICKS_BLOCK} from all three test configuration files; replaces the fork-block selection script invocation in the CI workflow with a pnpm install step, eliminating the separate block-selection phase.
Fork-block selection script with anchored relay-chain proof validation test/scripts/select-chopsticks-fork-block.ts	Imports blake2AsHex; adds SetValidationDataMetrics type; implements toU8a (trie node → bytes) and isProofAnchored (checks trie node hashes against relayParentStorageRoot); replaces descendants-only extraction with getSetValidationDataMetrics computing descendantsLength, relayChainTrieNodes, and proofAnchored; adds isStableForkBlock requiring anchored proof then branching on legacy (descendantsLength >= minDescendants) vs. production (descendantsLength === 0) format; updates --min-descendants CLI description and main scan loop to use the new metrics; updates terminal error to reflect anchored-proof and descendants requirements.
Test suite adaptation: relay-parent offset disabling and direct block creation test/suites/chopsticks/test-upgrade-chain.ts	Introduces disableRelayParentOffset helper that sets asyncBacking.relayParentOffset to 0 after runtime upgrade to avoid descendant-header verification failures; updates upgradeRuntime to call the helper immediately after the upgrade event; replaces all retry-helper-based block creation in test cases T1 and T2 with direct context.createBlock() calls (batched or per-iteration), removing the previous retry utilities.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• moonbeam-foundation/moonbeam#3740: The test suite changes adding disableRelayParentOffset directly exercise the runtime behavior where relay_parent_offset is sourced dynamically from AsyncBacking instead of a fixed constant.
• moonbeam-foundation/moonbeam#3757: Overlaps in test/suites/chopsticks/test-upgrade-chain.ts with modifications to block-production logic and retry-helper removal.
• moonbeam-foundation/moonbeam#3765: Directly precedes this PR — it introduced the original relayParentDescendants.length >= --min-descendants check that this PR extends with the anchored relay-chain state proof requirement.

Suggested labels

ci, D2-notlive

Suggested reviewers

• librelois

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately captures the main fix: resolving the Chopsticks runtime-upgrade test panic caused by InvalidNumberOfDescendants error.
Description check	✅ Passed	The description is comprehensive and directly related to the changeset, explaining the root cause, solution, and implementation details of the fix.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch artur/chopsticks-fork-block-fix

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}