Keep baseSlot when unfolding storage layouts

[Steve0x2a]

unfoldStorageLayout rebuilt the layout without baseSlot. getStorageLayout and the deprecated UpgradeableContract API both go through that, so validateBaseSlotUnchanged compared undefined to undefined and a changed layout at slot passed on the AST-only path.

Hardhat/CLI flows already have compiler layouts, so they were not affected.

Credit to @nahimterrazas for the report and the repro.

Fixes #1296

Summary by CodeRabbit

• Bug Fixes

  • Preserved storage layout base slots when unfolding and querying layouts.
  • Improved handling of flat and inherited storage layouts.
  • Continued detecting incompatible base slot changes during upgrade validation.

• Tests

  • Added regression coverage for base slot preservation and upgrade validation.

• Chores

  • Scheduled a patch release for the storage layout improvements.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 5111c829-73c5-45f2-98b6-942611cfac45

📥 Commits

Reviewing files that changed from the base of the PR and between 3aa87ac and 90dfcef.

📒 Files selected for processing (3)

• .changeset/keep-baseslot-on-unfold.md
• packages/core/src/storage-custom-layout.test.ts
• packages/core/src/validate/query.ts

Included review availability: Your plan includes up to 4 reviews per rolling hour; 3 remain after this review.

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Walkthrough

unfoldStorageLayout now preserves baseSlot for flat and inherited layouts. Regression tests verify preservation and confirm that storage-upgrade validation rejects changed base slots. A patch changeset documents the fix.

Changes

Storage-layout baseSlot preservation

Layer / File(s)	Summary
Preserve baseSlot during unfolding packages/core/src/validate/query.ts	unfoldStorageLayout copies baseSlot into flat and pre-flattened layouts.
Cover unfolded layout validation packages/core/src/storage-custom-layout.test.ts, .changeset/keep-baseslot-on-unfold.md	Tests cover flat and inherited layouts and verify that changed base slots raise a storage-upgrade error. The changeset records a patch release.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 90dfc

The change preserves base-slot information when unfolding storage layouts and adds focused coverage for validation paths; no actionable merge-blocking risk remains beyond normal checks and review.

Possibly related PRs

• OpenZeppelin/openzeppelin-upgrades#1253: Both changes preserve and validate ERC-7201 baseSlot values during storage-layout processing.

Poem

A rabbit saw a slot unfold,
Its base stayed true, its tale was told.
Flat or nested, none went astray,
Changed slots now block the upgrade way.
Hop, hop—layouts behave today! 🐇

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes preserve baseSlot in both unfolding branches and add coverage for getStorageLayout and AST-only validation paths [#1296].
Out of Scope Changes check	✅ Passed	The changeset, implementation, and regression tests directly support the linked issue and PR objectives.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: preserving baseSlot when unfolding storage layouts.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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