Add ERC: Partial and Extended ERC-4626 Vaults

ERCS/erc-7575.md

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+---
+eip: 7575
+title: Partial and Extended ERC-4626 Vaults
+description: Modular ERC-4626 Interface enabling Multi-Vault, Pipes, Partial and Alternative Vaults
+author: Jeroen Offerijns (@hieronx), Alina Sinelnikova (@ilinzweilin), Vikram Arun (@vikramarun), Joey Santoro (@joeysantoro), Farhaan Ali (@0xfarhaan)
+discussions-to: https://ethereum-magicians.org/t/erc-7575-partial-and-extended-erc-4626-vaults/17274
+status: Draft
+type: Standards Track
+category: ERC
+created: 2023-12-11
+requires: 20, 165, 2771, 4626
+---
+
+## Abstract
+
+The following standard adapts [ERC-4626](./eip-4626.md) into several modular components which can be used in isolation or combination to unlock new use cases.
+
+New functionality includes multiple assets or entry points for the same share token, conversions between arbitrary tokens, and implementations which use partial entry/exit flows from ERC-4626.
+
+This standard adds nomenclature for the different components/interfaces of the base ERC-4626 standard including `ERC7575MinimalVaultInterface` and an interface for each entry/exit function.
+
+It adds a new `share` method to allow the [ERC-20](./eip-20.md) dependency to be externalized.
+
+Lastly, it enforces [ERC-165](./eip-165.md) support for Vaults.
+
+## Motivation
+
+[ERC-4626](./eip-4626.md) represents a "complete" and symmetrical standard for a Tokenized Vault pattern. Certain use cases may want to borrow functionality from 4626 to maintain some interface compatibility without wanting the entire standard.
+
+One major use case are Vaults which have multiple assets or entry points such as liquidity provider (LP) Tokens. These are generally unwieldy or non-compliant due to the requirement of ERC-4626 to itself be an ERC-20.
+
+Another are Vaults which don't have a true share token but rather convert between two arbitrary external tokens.
+
+Some Vaults always have a 1:1 conversion rate between `assets` and `shares` and would benefit from being able to implement only one entry or exit function from the Vault rather than both.
+
+There are so many customizeable use cases that it is beneficial to modularize the Vault standard.
+
+## Specification
+
+### Definitions:
+
+The existing definitions from [ERC-4626](./eip-4626.md) apply.
+
+- Multi-Vault: A Vault which has multiple assets/entry points
+- Pipe: A converter from one token to another (unidirectional or bidirectional)
+- Entry Function: A Vault function which converts `asset` to `shares`. Either `deposit` or `mint` in ERC-4626
+- Exit Function: A Vault function which converts `shares` to `assets`. Either `withdraw` or `redeem` in ERC-4626
+- Partial Vault: A Vault which implements only one Entry or Exit function from ERC-4626
+
+First the standard defines a new `share` function which is useful for many configurable use cases, and then goes into detail on the requirements for different configurations.
+
+### Methods
+
+#### share
+
+The address of the underlying `share` received on deposit into the Vault. MUST return an address of an ERC-20 share representation of the Vault.
+
+`share` MAY return the address of the Vault itself.
+
+If the `share` returns an external token i.e. `share != address(this)`:
+* entry functions MUST increase the `share` balance of the `receiver` by the `shares` amount. i.e. `share.balanceOf(receiver) += shares`
+* exit functions MUST decrease the `share` balance of the `owner` by the `shares` amount. i.e. `share.balanceOf(owner) -= shares`
+
+MUST _NOT_ revert.
+
+```yaml
+- name: share
+  type: function
+  stateMutability: view
+
+  inputs: []
+  outputs:
+    - name: shareTokenAddress
+      type: address
+```
+
+### `ERC7575MinimalVault` Interface
+The Minimal Vault Interface consists of the methods which are required for any `share` based Vault with a corresponding deposit `asset`.
+
+It is defined as the following ERC-4626 methods (and `share` described above):
+- `asset`
+- `share`
+- `convertToAssets`
+- `convertToShares`
+- `totalAssets`
+
+It also includes the `Deposit` and `Withdraw` events.
+
+### Partial Vault Interfaces
+A Partial Vault omits at least one of the ERC-4626 entry or exit functions.
+
+A Partial Vault MUST implement both the `preview*` and `max*` methods associated with any implemented entry/exit functions.
+
+Partial Vaults SHOULD prefer implementing `deposit` and `redeem` over `mint` and `withdraw`, respectively.
+
+A Partial Vault MAY implement none of the ERC-4626 entry or exit functions and instead use a bespoke entry/exit. In this case it still MUST implement `ERC7575MinimalVault` interface. Any bespoke entry/exit from the Vault MUST emit `Deposit` or `Withdraw`, respectively.
+
+This standard defines four modular interfaces beyond the Minimal Vault Interface:
+- `ERC7575DepositVault` - `deposit`, `previewDeposit`, `maxDeposit`
+- `ERC7575MintVault` - `mint`, `previewMint`, `maxMint`
+- `ERC7575RedeemVault` - `redeem`, `previewRedeem`, `maxRedeem`
+- `ERC7575WithdrawVault` - `withdraw`, `previewWithdraw`, `maxWithdraw`
+
+### Multi-Vaults
+Multi-vaults share a single `share` token with multiple entry points denominated in different `asset` tokens.
+
+Multi-vaults MUST implement the `share` method on each entry point. The entry points SHOULD NOT be ERC-20.
+
+### Pipes
+Pipes convert between a single `asset` and `share` which are both ERC-20 tokens outside the Vault.
+
+A Pipe MAY be either unidirectional or bidirectional.
+
+If the exchange rate is fixed, the Pipe SHOULD be a Partial Vault implementing only `deposit` and/or `redeem`.
+
+A unidirectional Pipe SHOULD implement only the entry function(s) `deposit` and/or `mint`.
+
+### [ERC-165](./eip-165.md) support
+
+Smart contracts implementing any of the above Vault interfaces MUST implement the [ERC-165](./eip-165.md) `supportsInterface` function.
+
+`ERC7575MinimalVault` MUST return the constant value `true` if `0x50a526d6` is passed through the `interfaceID` argument.
+
+`ERC7575DepositVault` MUST return the constant value `true` if `0xc1f329ef` is passed through the `interfaceID` argument.
+
+`ERC7575MintVault` MUST return the constant value `true` if `0xe1550342 ` is passed through the `interfaceID` argument.
+
+`ERC7575RedeemVault` MUST return the constant value `true` if `0x2fd7d42a ` is passed through the `interfaceID` argument.
+
+`ERC7575WithdrawVault` MUST return the constant value `true` if `0x70dec094 ` is passed through the `interfaceID` argument.
+
+If a Vault implements all 5 interfaces, it MUST also return the constant value `true` if `0x2f0a18c5` is passed through the `interfaceID` argument. This value is the chained XOR of all 5 interfaces, i.e. the [ERC-165](./eip-165.md) compliant `interfaceID` for the complete [ERC-7575](./eip-7575.md) implementation.
+
+## Rationale
+
+This standard is intentionally flexible to support both existing [ERC-4626](./eip-4626.md) Vaults easily by the introduction of a single new method, but also flexible to support new use cases by allowing separate share tokens.
+
+### Ability to externalize [ERC-20](./eip-20.md) Dependency
+By allowing `share != address(this)`, the Vault can have an external contract managing the [ERC-20](./eip-20.md) functionality of the Share. In the case of Multi-Vaults, this avoids the confusion that might arise if each Vault itself were required to be an [ERC-20](./eip-20.md), which could cause confusion for integrators and front-ends. This approach also enables the creation of new types of Vaults, such as Pipes, which facilitate the conversion between two external [ERC-20](./eip-20.md) tokens.
+
+
+## Backwards Compatibility
+
+Existing [ERC-4626](./eip-4626.md) Vaults can be made compatible with ERC-x by adding a single `share` method that returns the address of the Vault.
+
+## Security Considerations
+
+[ERC-20](./eip-20.md) non-compliant Vaults must take care with supporting a redeem flow where `owner` is not `msg.sender`, since the [ERC-20](./eip-20.md) approval flow does not by itself work if the Vault and share are separate contracts. It can work by setting up the Vault as a Trusted Forwarder of the share token, using [ERC-2771](./eip-2771.md).
+
+## Copyright
+
+Copyright and related rights waived via [CC0](../LICENSE.md).