[Flow EVM] Implement ABI encoding/decoding for arrays of Solidity tuples

[m-Peter]

Closes: #8370
Related: onflow/FlowYieldVaultsEVM#40

Summary by CodeRabbit

• New Features

  • Support for encoding and decoding Cadence structs as EVM-compatible tuples in ABI operations, including proper handling of struct arrays for correct roundtrip conversion.

• Tests

  • Added test coverage validating ABI encoding and decoding of arrays of structs, ensuring roundtrip fidelity.

[coderabbitai]

📝 Walkthrough

Walkthrough

Added context-aware type resolution and tuple-detection to ABI encoding/decoding, enabling Cadence struct arrays to be encoded/decoded as Solidity tuples by plumbing context through goType and adjusting array element handling for tuple-encodable composites.

Changes

Cohort / File(s)	Summary
ABI encoding core fvm/evm/impl/abi.go	Added context parameter to goType; perform geth ABI lookup and return tuple types for tuple-encodable composites; propagate context through recursive calls; detect isTuple for composite element types and adjust array element encoding (pointer indirection when tuple-backed).
Tests fvm/evm/stdlib/contract_test.go	Added two test blocks asserting ABI encode/decode roundtrip for arrays of structs mapped to Solidity tuple types, verifying element values and gas gauge totals.

Sequence Diagram(s)

sequenceDiagram
    participant Client as Input: Cadence Array
    participant Encoder as ABI Encoder
    participant TypeResolver as goType (with context)
    participant ElementHandler as Element Encoder
    participant Output as EVM Bytes

    Client->>Encoder: encodeABI([struct1, struct2,...])
    Encoder->>TypeResolver: goType(context, arrayElementType, evmTypeIDs)
    TypeResolver->>TypeResolver: resolve basic type / geth ABI type
    TypeResolver-->>Encoder: reflect.Type (+ isTuple flag if tuple-encodable)
    Encoder->>ElementHandler: iterate elements
    ElementHandler->>ElementHandler: if isTuple => indirect pointer if needed
    ElementHandler-->>Encoder: prepared element values
    Encoder->>Output: pack elements as tuple-encoded ABI
    Output-->>Client: return encoded bytes

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Suggested reviewers

• janezpodhostnik
• holyfuchs
• fxamacker

Poem

🐰 I hopped through types with a curious stare,
Context in paw and tuples to share,
Arrays of structs now snug in a row,
Encoded as tuples — off they go! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and specifically describes the main change: implementing ABI encoding/decoding for arrays of Solidity tuples, which matches the pull request objectives.
Linked Issues check	✅ Passed	The code changes successfully implement ABI encoding/decoding for arrays of Solidity tuples as required by issue #8370, with context parameter propagation and tuple-aware array handling.
Out of Scope Changes check	✅ Passed	All changes are directly related to the objective of enabling ABI encoding/decoding for arrays of Solidity tuples; no out-of-scope modifications detected.

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

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch mpeter/abi-encode-tuple-arrays

---

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.}

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
fvm/evm/impl/abi.go	0.00%	18 Missing ⚠️

📢 Thoughts on this report? Let us know!

[zhangchiqing]

In the case where compositeType != nil , we are not making use of the compositeType, instead, we are reading from the staticType and context all over again.

I feel we might be able to get rid of this check, just rely on gethABIType to return ok, and check if ok == true, for when the type is a tuple. In other words, if compositeType != nil, then ok must be true, and if it's false, then it should be a fatal error, no?

Thoughts?

[m-Peter]

That's a good idea @zhangchiqing 🚀 gethABIType already makes the necessary check by calling asTupleEncodableCompositeType, so no need to do it here again. This also has the advantage that we can perform this check without caring about the special/reserved Cadence structs defined on the EVM system contract.

Updated in 4ccde5a .

[turbolent]

Nice!