token/p-token/src/processor/initialize_immutable_owner.rs

use pinocchio::{account_info::AccountInfo, msg, program_error::ProgramError, ProgramResult};
use token_interface::{
    error::TokenError,
    state::{account::Account, load_unchecked, Initializable},
};

#[inline(always)]
pub fn process_initialize_immutable_owner(accounts: &[AccountInfo]) -> ProgramResult {
    let token_account_info = accounts.first().ok_or(ProgramError::NotEnoughAccountKeys)?;

    // SAFETY: single immutable borrow to `token_account_info` account data.
    let account = unsafe { load_unchecked::<Account>(token_account_info.borrow_data_unchecked())? };

    if account.is_initialized() {
        return Err(TokenError::AlreadyInUse.into());
    }
    msg!("Please upgrade to SPL Token 2022 for immutable owner support");
    Ok(())
}