[review] MIP-52: Aptos Gas Pool

MIP/mip-n/README.md

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+# MIP-52: Aptos Gas Pool
+- **Description**: Introduces implementation specification for the Gas Pool in Aptos. 
+- **Authors**: [Liam Monninger](mailto:liam@movementlabs.xyz)
+- **Reviewer**: Andreas Penzkofer
+- **Desiderata**: [MD-38](https://github.com/movementlabsxyz/MIP/pulls)
+
+## Abstract
+
+We propose a means of implementing a Gas Pool in Aptos to satisfy the token recirculation requirements indicated in [MD-38](https://github.com/movementlabsxyz/MIP/pulls). This solution will allow for gas used to be stored in the pool. The re-use of said gas is not a subject of this MIP. However, [MIP-44](https://github.com/movementlabsxyz/MIP/pull/44), [MIP-41](https://github.com/movementlabsxyz/MIP/pull/41), et al.  provide suggestions to this end.
+
+## Motivation
+
+The introduction of a Gas Pool in Aptos will allow for the recirculation of gas used in the Aptos ecosystem. This ensures the supply can remain fixed and the gas can be re-used for purposes such as rewarding. 
+
+## Specification
+
+Aptos pays gas in the [epilogue](https://github.com/movementlabsxyz/aptos-core/blob/70be3926ff79ff4cdb0cee928f717fafcd41ecdd/aptos-move/aptos-vm/src/transaction_validation.rs#L194) of a transaction [dispatching](https://github.com/movementlabsxyz/aptos-core/blob/70be3926ff79ff4cdb0cee928f717fafcd41ecdd/aptos-move/aptos-vm/src/transaction_validation.rs#L34) to [`epilogue_gas_payer`](https://github.com/movementlabsxyz/aptos-core/blob/70be3926ff79ff4cdb0cee928f717fafcd41ecdd/aptos-move/framework/aptos-framework/sources/transaction_validation.move#L274). Depending on the [validator reward setting](https://github.com/movementlabsxyz/aptos-core/blob/70be3926ff79ff4cdb0cee928f717fafcd41ecdd/aptos-move/framework/aptos-framework/sources/transaction_validation.move#L305), [`epilogue_gas_payer`](https://github.com/movementlabsxyz/aptos-core/blob/70be3926ff79ff4cdb0cee928f717fafcd41ecdd/aptos-move/framework/aptos-framework/sources/transaction_validation.move#L274) will either call `transaction_fee::collect_fee` or `transaction_fee::burn_fee`. 
+
+At the time of writing the `transaction_fee::collect_fee` path is still experimental. 
+
+[`transaction_fee::burn_fee`](https://github.com/movementlabsxyz/aptos-core/blob/70be3926ff79ff4cdb0cee928f717fafcd41ecdd/aptos-move/framework/aptos-framework/sources/transaction_fee.move#L218) internally calls [`coin::burn_from`](https://github.com/movementlabsxyz/aptos-core/blob/70be3926ff79ff4cdb0cee928f717fafcd41ecdd/aptos-move/framework/aptos-framework/sources/transaction_fee.move#L229C17-L233C19) which can be replaced with a transfer.
+
+We thus suggest two paths to implement the Gas Pool in Aptos: 
+- **Custom Rewards Collection**
+- **Burn Replacement**
+
+### Custom Rewards Collection
+The custom rewards collection approach replaces Aptos' experimental `transaction_fee::collect_fee` with a custom rewards collection mechanism. This mechanism calls `coin::transfer_from` to move the gas to the Gas Pool at a known address.
+
+Coin burning logic can be kept in place and a similar features-based approach can be used to determine ensure the `transaction_fee::collect_fee` approach is used.
+
+### Burn Replacement
+The burn replacement approach replaces the `coin::burn_from` call in `transaction_fee::burn_fee` with a `coin::transfer_from` call to the Gas Pool.
+
+## Verification
+**Outstanding**:
+- Verify that the AptosVM does not validate burns. Otherwise, there may be logic outside of the framework `epilogue_gas_payer` path which needs to be updated. 
+- Identify any sponsorship or other gas payment mechanisms which may need to be updated to use the Gas Pool.
+
+## Errata
+
+
+## Appendix