Amendment fixFrozenLPTokenTransfer: Prohibit transfer of LPToken when an asset is frozen

[shawnxie999]

High Level Overview of Change

New Definition

If a liquidity pool token (LPToken) is associated with a liquidity pool that contains at least one asset that is regularly frozen, the LPToken itself is considered "frozen". This means:

1. The holder cannot send the frozen LPToken to others. (The frozen status restricts the holder from transferring the LPToken to another wallet)

2. The holder can still receive frozen LPTokens. (If someone sends frozen LPTokens to the holder, they can still receive them, even though they cannot send them out)

This behavior is similar to how regular frozen IOUs work: you can receive them, but you cannot send them to others while they are frozen.

Background

Prior to this amendment, a blacklisted account that owns frozen LPTokens could still transfer them through mechanisms such as Payments, Checks, Offers, or NFTs. This loophole allowed the recipient of these LPTokens to redeem or withdraw the underlying assets of the pool, bypassing the restrictions that should have applied to the blacklisted account. This behavior undermines the freezing mechanism's integrity and creates inconsistencies in asset control.

Note: this amendment only works with the existing regular freeze, and has no correlation with deep-freeze

Example

1. Alice deposits XRP and USD into an AMM pool.
2. The USD issuer freezes Alice's USD trustline.
3. Alice transfers her LPToken to Bob (although Alice cannot transfer USD directly, she can still transfer the LPToken).
4. Bob redeems USD using the received LPToken, effectively bypassing the freezing restrictions imposed on Alice.

Amendment changes

This amendment ensures that frozen LPTokens cannot be transferred. Below are the changes to specific transaction types:

Payments

• A blacklisted account can no longer send frozen LPTokens through direct payment.
• Offers attempting to sell frozen LPTokens can no longer be consumed on the DEX.

OfferCreate

• Accounts are prohibited from creating offers that attempt to sell frozen LPTokens.

CheckCash

• Cashing a check fails if it attempts to cash a frozen LPToken from the sender.

NFTokenCreateOffer

• Buyers are prohibited from creating buy offers involving frozen LPTokens.

NFTokenAcceptOffer

• Buyers cannot accept a sell offer if the offer requires the use of frozen LPTokens as payment.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Performance (increase or change in throughput and/or latency)
• Tests (you added tests for code that already exists, or your new feature included in this PR)
• Documentation update
• Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• Release

API Impact

• Public API: New feature (new methods and/or new fields)
• Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• Peer protocol change (must be backward compatible or bump the peer protocol version)

[codecov]

Codecov Report

Attention: Patch coverage is 91.83673% with 4 lines in your changes missing coverage. Please review.

Project coverage is 78.2%. Comparing base (f6d6308) to head (ceaa99d).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/xrpld/app/misc/detail/AMMUtils.cpp	81.0%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #5227   +/-   ##
=======================================
  Coverage     78.1%   78.2%           
=======================================
  Files          790     790           
  Lines        67562   67607   +45     
  Branches      8160    8161    +1     
=======================================
+ Hits         52791   52837   +46     
+ Misses       14771   14770    -1     

Files with missing lines	Coverage Δ
include/xrpl/protocol/Feature.h	100.0% <ø> (ø)
src/xrpld/app/paths/detail/DirectStep.cpp	82.5% <100.0%> (ø)
src/xrpld/app/paths/detail/StepChecks.h	100.0% <100.0%> (ø)
src/xrpld/ledger/View.h	100.0% <ø> (ø)
src/xrpld/ledger/detail/View.cpp	91.4% <100.0%> (+0.2%)	⬆️
src/xrpld/app/misc/detail/AMMUtils.cpp	97.4% <81.0%> (-2.1%)	⬇️

... and 4 files with indirect coverage changes

[yinyiqian1]

It looks functionally fine to me. Just left some comments about style, code coverage and redundant header files included.

[yinyiqian1]

just replied one comment. it looks good to me.

[vvysokikh1]

It looks good to me

[shawnxie999]

@bthomee commit msg:

Prohibit LPToken holders from sending LPToken to others if they have been frozen by one of the assets in AMM pool

We can use the amendment name for the descripton/title