chore: model pre-gloas block index as number

[twoeths]

Motivation

• right now we model both pre-gloas and gloas variants as Array, which has some disadvantages:
  • array type is too general, it could be 1000 items while we only have 1/2/3 items
  • item 0 of pre-gloas block is FULL variant index, while item 0 of gloas blocks is PENDING variant index which is a little bit confusing to maintain
  • we check lengh=1 as pre-gloas, which is correct based on the implementation but ideally we can do better typing to know it

Description

• model pre-gloas variant index as number
• model gloas variants using tuple: [number, number] or [number, number, number]

part of #8739

cc @ensi321 @nflaig

[gemini-code-assist]

Summary of Changes

Hello @twoeths, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the type safety and clarity of how block variant indices are managed within the ForkChoice and ProtoArray components. By explicitly typing pre-Gloas blocks with a single number and post-Gloas blocks with tuples, it resolves ambiguities and reduces potential confusion associated with array-based indexing, leading to more robust and maintainable code. This change streamlines the internal representation and handling of block variants, making the codebase easier to understand and less prone to type-related errors.

Highlights

• Improved Type Safety for Block Variant Indices: The representation of block variant indices has been refactored to explicitly distinguish between 'pre-Gloas' and 'post-Gloas' blocks, enhancing type safety and clarity.
• Pre-Gloas Variant Index as Number: For 'pre-Gloas' blocks, the variant index is now modeled as a single number instead of a single-element array, simplifying its usage and reducing ambiguity.
• Post-Gloas Variant Indices as Tuples: For 'post-Gloas' blocks, variant indices are now explicitly typed as tuples, specifically [number, number] or [number, number, number], providing a fixed structure and better type inference.
• Logic Adaptation for New Types: Existing logic within ForkChoice and ProtoArray classes has been updated to correctly handle the new VariantIndices type, utilizing Array.isArray() checks to differentiate between single numbers and arrays/tuples.

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Changelog

• packages/fork-choice/src/forkChoice/forkChoice.ts
  • Updated findNodeByBlockHash to correctly process variantIndices which can now be either a number or an array.
  • Modified forwardIterateDescendants to accommodate the new VariantIndices type for blockVariants.
  • Added a TODO comment to forwardIterateDescendants to address its ambiguity regarding consumer payload requirements.
• packages/fork-choice/src/protoArray/protoArray.ts
  • Introduced new type aliases: PreGloasVariantIndex (number), GloasVariantIndices (tuple types), and VariantIndices (union type) for improved type definition.
  • Changed the indices map from Map<RootHex, number[]> to Map<RootHex, VariantIndices> to leverage the new type system.
  • Refactored getNodeIndexByRootAndStatus, getDefaultVariant, getPayloadStatus, prune, getAncestor, getAncestor (second instance), and getAncestor (third instance) functions to correctly handle the new VariantIndices type using Array.isArray() checks.
  • Simplified the storage mechanism for variant indices in addGloasBlock and addPreGloasBlock to directly assign tuples or numbers, aligning with the new type definitions.

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[gemini-code-assist]

Code Review

This pull request is a great step towards improving type safety by modeling pre-Gloas block indices as a number and Gloas variants as tuples. The changes are consistently applied and enhance code clarity. However, I've identified a critical bug in the maybePrune function's logic for adjusting indices, where the wrong variable is used within a map callback. This could lead to incorrect pruning behavior. Please see the specific comment for details and a suggested fix.