#35229 refactor: Use CBlockIndex parameters as reference

• Prevent accidental null dereferences by enforcing non-null invariants at compile time
• Protects developers from runtime null errors across chain and index logic

This PR converts `const CBlockIndex*` parameters to `const CBlockIndex&` across several internal methods in validation, p2p, and indexes where null pointers are not permissible. It also updates `CChain::vChain` to hold `std::reference_wrapper<CBlockIndex>` elements instead of bare pointers to enforce non-null invariants.

Problem: Functions that expect valid block index pointers currently accept nullable pointer types, which requires implicit assumptions or runtime checks rather than compile-time enforcement of non-nullness.

P4 · cleanup

• P4 because method signature changes here have no impact on index correctness or sync speed
• Provides only minor maintainability value without altering how block filters or indexes run

Changing block filter index method arguments from pointer to reference is a cosmetic type-safety cleanup with no measurable index performance or correctness impact.

Membership: Modifies BaseIndex::ProcessBlock and BlockFilterIndex::LookupFilterRange signatures in src/index/.

Factors: security/stability 0, bug 0, performance 0, user value 0, leverage 0

P4 · cleanup

• Converting pointer arguments in PeerManagerImpl to references is a minor internal refactor that does not modify peer relay or network behavior.

Converting pointer arguments in PeerManagerImpl to references is a minor internal refactor that does not modify peer relay or network behavior.

Membership: Updates internal block download helper signatures in src/net_processing.cpp.

Factors: security/stability 0, bug 0, performance 0, user value 0, leverage 0

P4 · cleanup

• P4 because it is a routine internal cleanup with no consensus bug fixes or performance gains
• The benefit is limited to compile-time safety checks within internal chain state management

Replacing CBlockIndex pointers with references and std::reference_wrapper in CChain is an internal janitorial cleanup that does not alter consensus or chain validation rules.

Membership: Modifies CChain internal container and LastCommonAncestor in src/chain.cpp and src/chain.h.

Factors: security/stability 0, bug 0, performance 0, user value 0, leverage 0

• Author has been silent for 113 days, exceeding the stale author threshold
• Reviewing now may be unproductive until the author returns to address feedback

The author has been silent for 113 days since the last push on 2026-05-27, exceeding the 60-day project staleness threshold.

Author status: silent since 2026-05-27

Resolved concerns:

• maflcko pointed out confusion around LastCommonAncestor return invariants; author changed Assume to Assert and clarified the shared genesis requirement.
• maflcko suggested using std::reference_wrapper in CChain to enforce non-nullness without comment reliance; author implemented it in CChain::vChain.

• Concept approved with broad agreement and no objections raised
• Support for compile-time safety and clearer non-null guarantees (musaHaruna)
• Concept approval without stated reasons (stickies-v, w0xlt)
• Suggested using reference wrappers for internal chain storage (maflcko)

Strong concept agreement from multiple reviewers; inline comments on invariants resolved by author pushes.

Multiple contributors gave Concept ACKs, with musaHaruna articulating clear benefits for non-null compile-time guarantees. The technical feedback from maflcko was incorporated into subsequent commits.

• musaHaruna (2026-05-19): 'Changing parameters from const CBlockIndex* to const CBlockIndex& where nullptr is not a valid state improves clarity and gives stronger compile-time guarantees'
• stickies-v (2026-05-07): 'Concept ACK'
• w0xlt (2026-06-14): 'Concept ACK'

Objections:

Support:

• musaHaruna: Changing parameters from const CBlockIndex* to const CBlockIndex& where nullptr is not a valid state improves clarity and gives stronger compile-time guarantees around non-nullability
• stickies-v: Concept ACK [not substantive]
• w0xlt: Concept ACK [not substantive]

Participants: stickies-v (support), musaHaruna (support), maflcko (objection), w0xlt (support)

State derived from the lists: substantive support, no open objection (musaHaruna)

Review verdicts (DrahtBot): 0

• Concept ACK: stickies-v, musaHaruna, w0xlt

14 lines under test/bench/ci.

• src/net_processing.cpp +24/-20
• src/chain.cpp +14/-11
• src/index/base.cpp +9/-9
• src/index/blockfilterindex.cpp +8/-8
• src/chain.h +9/-6
• src/test/blockfilter_index_tests.cpp +6/-6
• src/index/blockfilterindex.h +2/-2
• src/rpc/blockchain.cpp +2/-1
• src/validation.cpp +1/-2
• src/index/base.h +1/-1
• src/node/interfaces.cpp +1/-1
• src/test/chain_tests.cpp +1/-1

This PR refactors several CBlockIndex parameter signatures across validation, p2p, and index modules from pointers to references to enforce non-nullness at compile time. It also updates CChain::vChain to hold std::reference_wrapper elements. Multiple reviewers have voiced concept support for the compile-time invariant enforcement, and initial technical feedback was addressed. However, the author has been inactive for over 110 days, making the pull request stale.