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

[m-Peter]

Closes: #8370
Related: onflow/FlowYieldVaultsEVM#40

Summary by CodeRabbit

• New Features

  • Added support for encoding and decoding Cadence structs as EVM-compatible tuples in ABI operations, enabling proper roundtrip conversion for struct arrays.

• Tests

  • Added test coverage for struct array encoding and decoding via ABI operations.

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[coderabbitai]

📝 Walkthrough

Walkthrough

The changes implement ABI encoding and decoding support for arrays of Solidity tuples. A context parameter was added to the type resolution function, tuple-encodable composite detection logic was introduced, and array element handling was updated to properly encode/decode struct arrays as tuple sequences.

Changes

Cohort / File(s)	Summary
ABI Encoding Implementation fvm/evm/impl/abi.go	Updated goType function signature to accept context parameter; added logic to detect and handle tuple-encodable Cadence composites; modified array encoding to pass context and conditionally indirect tuple elements from pointers.
Test Coverage fvm/evm/stdlib/contract_test.go	Added two test cases validating roundtrip ABI encoding/decoding of arrays containing structs mapped to Solidity tuples; tests verify element values are preserved through encode/decode cycles.

Sequence Diagram(s)

sequenceDiagram
    participant Client as Input: Cadence Array
    participant Encoder as ABI Encoder
    participant TypeResolver as Type Resolver (goType)
    participant ElementHandler as Element Processor
    participant Output as Output: EVM Bytes

    Client->>Encoder: encodeABI([struct1, struct2, ...])
    Encoder->>TypeResolver: goType(context, arrayType)
    TypeResolver->>TypeResolver: Detect tuple-encodable composite
    TypeResolver-->>Encoder: Return array of tuple type
    
    Encoder->>ElementHandler: For each struct element
    ElementHandler->>ElementHandler: Check isTuple flag
    ElementHandler->>ElementHandler: Indirect from pointer if needed
    ElementHandler-->>Encoder: Processed element
    
    Encoder->>Output: Encode to EVM tuple format
    Output-->>Client: Return encoded ABI bytes

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Suggested reviewers

• janezpodhostnik
• holyfuchs
• zhangchiqing
• fxamacker

Poem

🐰 A hop and a skip through struct arrays we go,
Tuples take shape as the encodings flow,
Context-aware paths where the types align,
Cadence and Solidity now intertwine! ✨

🚥 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 describes the main change: implementing ABI encoding/decoding for arrays of Solidity tuples, which is the primary objective of the PR.
Linked Issues check	✅ Passed	The PR implementation matches the linked issue #8370 requirement to add ABI encoding/decoding support for arrays of Solidity tuples, with corresponding test coverage.
Out of Scope Changes check	✅ Passed	All changes are directly related to implementing tuple array encoding/decoding: updated goType function signature, added tuple detection logic, adjusted element handling, and added comprehensive test cases.

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✨ 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

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[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 21 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
fvm/evm/impl/abi.go	0.00%	21 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?