test(lotus_json): assert LotusJson<Option<T>> is nullable in schema

[0xDevNinja]

Summary

Closes #4331.

LotusJson<Option<T>> delegates its schema to Option<T::LotusJson>, which schemars already renders as nullable ("type": [..., "null"] / a null branch in anyOf). This adds a small regression test locking that behaviour in, as suggested in the issue — verifying that:

• LotusJson<Option<T>> produces a schema that permits null (i.e. is optional in the OpenRPC spec), and
• the non-optional LotusJson<T> counterpart does not permit null.

The helper schema_allows_null accepts both the "type" union form (used for primitives/arrays) and the anyOf/oneOf form (used for $ref object types), so the test stays robust across inner types.

No production code changes — test only.

Reference tests

cargo test -p forest-filecoin --lib lotus_json::opt:: — 3 passed (existing snapshot + quickcheck, plus the new optional_is_nullable_in_schema).

Other information and links

Issue originally raised by @ruseinov in #4330 (comment).

Summary by CodeRabbit

• Tests
  • Added regression coverage ensuring optional Lotus JSON values accept null in generated JSON/OpenRPC schemas.
  • Verified non-optional Lotus JSON values do not permit null in the corresponding schemas.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: adda3c4f-e1a7-4a4f-a6c8-69686bd232ac

📥 Commits

Reviewing files that changed from the base of the PR and between de41e74 and 375530d.

📒 Files selected for processing (1)

• src/lotus_json/opt.rs

🔗 Linked repositories identified

CodeRabbit considers these linked repositories for cross-repo context during reviews:

• filecoin-project/lotus (manual)

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Walkthrough

Changes

LotusJson schema nullability

Layer / File(s)	Summary
Schema nullability regression coverage src/lotus_json/opt.rs	Adds schema_allows_null and verifies that LotusJson<Option<Cid>> accepts null, while LotusJson<Cid> does not.

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

Suggested reviewers: hanabi1224

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly states the main change: a regression test asserting LotusJson<Option> is nullable in schema.
Linked Issues check	✅ Passed	The new regression test verifies LotusJson<Option> is nullable in the OpenRPC schema as requested by #4331.
Out of Scope Changes check	✅ Passed	The changes stay within scope by adding only a test and test helper for schema nullability.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

✨ Simplify code

• Create PR with simplified code

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[hanabi1224]

LGTM, thanks! There is an outstanding lint issue to fix tho.

[codecov]

Codecov Report

❌ Patch coverage is 80.95238% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.05%. Comparing base (17c49db) to head (375530d).
⚠️ Report is 29 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/lotus_json/opt.rs	80.95%	4 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/lotus_json/opt.rs	83.33% <80.95%> (-3.34%)	⬇️

... and 62 files with indirect coverage changes

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[sudo-shashank]

lint:spellcheck failing

[0xDevNinja]

Good catch, thanks. Fixed the spellcheck failure by rewording the doc comment to avoid the word that tripped the dictionary. Should be green now.