Merge bitcoin/bitcoin#17786: refactor: Nuke policy/fees->mempool circular dependencies

[DashCoreAutoGuix]

Backports bitcoin#17786

This PR:

• Gets rid of the policy/fees -> txmempool -> policy/fees circular dependency
• Moves CTxMemPoolEntry class to its own module (txmempool_entry.h)
• Inlines the class's functions

Original Bitcoin PR: bitcoin#17786
Original commit: d0b1f61

Dash-specific adaptations:

• Preserved Dash's size-based fee calculation (nTxSize/sigOpCount) instead of Bitcoin's weight-based (nTxWeight/sigOpCost)
• Added Dash-specific fields to CTxMemPoolEntry: validForProTxKey, isKeyChangeProTx
• Kept existing src/policy/rbf.cpp and src/test/fuzz/util/mempool.cpp files that were already present

Summary by CodeRabbit

Release Notes

Refactor

• Reorganized transaction mempool entry handling into separate internal modules
• Restructured Replace-By-Fee policy validation logic for improved maintainability
• Eliminated circular dependency in internal module structure
• Updated test infrastructure and sanitizer suppressions

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

This refactoring extracts the CTxMemPoolEntry class definition from src/txmempool.h into a dedicated new header src/txmempool_entry.h. Multiple source files are updated to include the new header. A new RBF (Replace-By-Fee) policy implementation file is added with several validation functions. Method implementations are adjusted accordingly.

Changes

Cohort / File(s)	Summary
Header extraction and reorganization src/txmempool_entry.h	New public header file introducing the CTxMemPoolEntry class with comprehensive mempool entry state management, including fee tracking, ancestor/descendant statistics, lock points, and mempool relationships. Also defines LockPoints struct and CompareIteratorByHash comparator.
	src/txmempool.h
	src/Makefile.am
RBF policy logic src/policy/rbf.cpp	New implementation file containing eight RBF validation functions: IsRBFOptIn(), IsRBFOptInEmptyMempool(), GetEntriesForConflicts(), HasNoNewUnconfirmed(), EntriesAndTxidsDisjoint(), PaysMoreThanConflicts(), and PaysForRBF(). Functions use std::optional<std::string> for error reporting.
Mempool implementation src/txmempool.cpp	Removed public constructor CTxMemPoolEntry::CTxMemPoolEntry() and member functions UpdateModifiedFee(), UpdateLockPoints(), and GetTxSize().
Include directive additions src/bench/mempool_eviction.cpp, src/bench/mempool_stress.cpp, src/bench/rpc_mempool.cpp, src/net_processing.cpp, src/node/interfaces.cpp, src/rpc/mempool.cpp, src/test/util/setup_common.cpp, src/validation.cpp	Added #include <txmempool_entry.h> to access CTxMemPoolEntry type declarations.
Header replacement src/policy/fees.cpp	Replaced #include <txmempool.h> with #include <txmempool_entry.h>.
Test utilities src/test/fuzz/util/mempool.cpp	Added new helper function ConsumeTxMemPoolEntry() for fuzzing; generates randomized CTxMemPoolEntry instances from fuzzed data.
	src/test/fuzz/policy_estimator.cpp
Build and linting test/lint/lint-circular-dependencies.py	Removed expected circular dependency "policy/fees -> txmempool -> policy/fees".
	test/sanitizer_suppressions/ubsan

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~50 minutes

• src/policy/rbf.cpp: Requires detailed review of RBF validation logic, error handling paths, and feerate/fee sufficiency rules. Eight interdependent functions with optional error reporting.
• src/txmempool_entry.h: Large new header file with comprehensive CTxMemPoolEntry class definition, multiple accessors, mutators, and member tracking. Verify correctness of ancestor/descendant state tracking and mutable field semantics.
• Header extraction from src/txmempool.h: Verify that all moved definitions are correctly relocated and that remaining code in txmempool.h properly depends on the new external header.
• Method removals in src/txmempool.cpp: Confirm that removal of constructor and update methods does not break existing call sites and that alternative mechanisms handle fee/size propagation.
• Circular dependency removal: Verify that the lint change correctly reflects the architectural decoupling achieved by the header extraction.

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 38.89% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main refactoring objective: eliminating the circular dependency between policy/fees and mempool by moving CTxMemPoolEntry to its own header.

✨ 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 backport-0.25-batch-488-pr-17786

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