token-2022: [OS-SPL-ADV-00] Enable and fix account ordering on confidential transfer with split proofs

[samkim-crypto]

Problem

The accounts that are required for a confidential transfer with split proof are as follows:

    ///   1. `[writable]` The source SPL Token account.
    ///   2. `[]` The token mint.
    ///   3. `[writable]` The destination SPL Token account.
    ///   4. `[]` Context state account for
    ///      `VerifyCiphertextCommitmentEqualityProof`.
    ///   5. `[]` Context state account for
    ///      `VerifyBatchedGroupedCiphertext2HandlesValidityProof`.
    ///   6. `[]` Context state account for `VerifyBatchedRangeProofU128`.
    ///   7. `[signer]` The source account owner.
    ///   If `close_split_context_state_on_execution` is set, all context state
    ///     accounts must be `writable` and the following sequence
    ///     of accounts are needed:
    ///   8. `[]` The destination account for lamports from the context state
    ///      accounts.
    ///   9. `[signer]` The context state account owner.
    ///   10. `[]` The zk token proof program.

However, the actual instruction processor assumes that 7. [signer] The source account owner is assumed to be last in the order.

    ///   1. `[writable]` The source SPL Token account.
    ///   2. `[]` The token mint.
    ///   3. `[writable]` The destination SPL Token account.
    ///   4. `[]` Context state account for
    ///      `VerifyCiphertextCommitmentEqualityProof`.
    ///   5. `[]` Context state account for
    ///      `VerifyBatchedGroupedCiphertext2HandlesValidityProof`.
    ///   6. `[]` Context state account for `VerifyBatchedRangeProofU128`.
    ///   If `close_split_context_state_on_execution` is set, all context state
    ///     accounts must be `writable` and the following sequence
    ///     of accounts that are marked with asterisk are needed:
    ///   7*. `[]` The destination account for lamports from the context state
    ///      accounts.
    ///   8*. `[signer]` The context state account owner.
    ///   9*. `[]` The zk token proof program.
    ///   10. `[signer]` The source account owner.

This issue with the ordering of the accounts was left undetected because there were no tests for auto-close of context accounts. There were no tests for auto-close because auto-close was not enabled.

Solution

• Enabled auto-close of context accounts in the instruction processor logic
• Added tests for auto-close of context accounts
• Fixed the issue with the ordering of the accounts

[joncinque]

The core logic looks good! Just some suggestions to make the tests better

[joncinque]

Can you add checks at the end to make sure that the context accounts are cleaned up and alice is credited?

[samkim-crypto]

Yes that is good point. I added test to check for AccountNotFound, but let me know if there is a better way to test it.

[joncinque]

Those checks are great! Can you also check that the lamports were properly added to the destination?

[samkim-crypto]

Sorry I missed it! I followed how it is done in close_account.rs and checked that the lamport destination has positive number of lamports.

[joncinque]

Great!

[joncinque]

Same here, please add a check that it worked