is_signer field doesn't pass through CPI for UncheckedAccounts

[blockiosaurus]

When making a CPI call with an UncheckedAccount as signer, the is_signer field doesn't carry through the CPI and so the invoked instruction has no signer.

The current functioning workaround is to replace the CPI call with an invoke and manually copying the is_signer field to the passed-in account metas.

let ix = solana_program::instruction::Instruction {
        program_id: cpi_program.key(),
        accounts: cpi_accounts
            .to_account_metas(None)
            .into_iter()
            .zip(cpi_accounts.to_account_infos())
            .map(|mut pair| {
                pair.0.is_signer = pair.1.is_signer;
                pair.0
            })
            .collect(),
        data: ix_data.data(),
    };

    invoke(&ix, &cpi_accounts.to_account_infos())?;

[armaniferrante]

What about if you decorate it with #[account(signer)] ?

[blockiosaurus]

That works in most situations but doesn't cover the edge cases where there are multiple potential signers or optional signers.