feat: include errors in IDL

[thlorenz]

Finds enums marked with thiserror Error derive and consume each error attribute on the respective variant to extract error information.

Supports explicit and implicit variant discriminants as well as a mix of both, some examples it handles:

Implicit Discriminants (Error codes)

/// Errors that may be returned by the Vault program.
#[derive(Clone, Debug, Eq, Error, FromPrimitive, PartialEq)]
pub enum VaultError {
    /// Invalid instruction data passed in.
    #[error("Failed to unpack instruction data")]
    InstructionUnpackError,

    /// Lamport balance below rent-exempt threshold.
    #[error("Lamport balance below rent-exempt threshold")]
    NotRentExempt,
}

IDL:

{
  "version": "",
  "name": "",
  "instructions": [],
  "errors": [
    {
      "code": 0,
      "name": "InstructionUnpackError",
      "msg": "Failed to unpack instruction data"
    },
    {
      "code": 1,
      "name": "NotRentExempt",
      "msg": "Lamport balance below rent-exempt threshold"
    }
  ],
  "metadata": {
    "origin": "shank"
  }
}

Mixed Discriminants (Error Codes)

/// Errors that may be returned by the Vault program.
#[derive(Clone, Debug, Eq, Error, FromPrimitive, PartialEq)]
pub enum VaultError {
    /// Invalid instruction data passed in.
    #[error("Failed to unpack instruction data")]
    InstructionUnpackError = 3000,

    /// Lamport balance below rent-exempt threshold.
    #[error("Lamport balance below rent-exempt threshold")]
    NotRentExempt,

    /// Already initialized
    #[error("Already initialized")]
    AlreadyInitialized,

    /// Uninitialized
    #[error("Uninitialized")]
    Uninitialized,

    /// Account does not have correct owner
    #[error("Account does not have correct owner")]
    IncorrectOwner = 4000,

    /// NumericalOverflowError
    #[error("NumericalOverflowError")]
    NumericalOverflowError,
}

IDL

{
  "version": "",
  "name": "",
  "instructions": [],
  "errors": [
    {
      "code": 3000,
      "name": "InstructionUnpackError",
      "msg": "Failed to unpack instruction data"
    },
    {
      "code": 3001,
      "name": "NotRentExempt",
      "msg": "Lamport balance below rent-exempt threshold"
    },
    {
      "code": 3002,
      "name": "AlreadyInitialized",
      "msg": "Already initialized"
    },
    {
      "code": 3003,
      "name": "Uninitialized",
      "msg": "Uninitialized"
    },
    {
      "code": 4000,
      "name": "IncorrectOwner",
      "msg": "Account does not have correct owner"
    },
    {
      "code": 4001,
      "name": "NumericalOverflowError",
      "msg": "NumericalOverflowError"
    }
  ],
  "metadata": {
    "origin": "shank"
  }
}

Improvements

To extract correct error codes ParsedEnum was improved to handle multiple discriminant scenarios.

FIXES: https://github.com/metaplex-foundation/metaplex-program-library/issues/261