Nesting instruction calls with different signers

Question

I have an Anchor program where one of the instruction calls another like so:

#[program]
pub mod dippies_index_protocol {
    use super::*;

    pub fn foo(
        ctx: Context<Foo>,
    ) -> Result<()> {
        instructions::bar(ctx)
    }

    pub fn bar(
        ctx: Context<Bar>,
    ) -> Result<()> {
        Ok(())
    }
}

However, I want the signer of the foo instruction to be the signer of the transaction, and the signer of the bar transaction when called by foo to be a PDA.

I can't use CpiContext::new_with_signer because it's not a cross program invocation, I can't instantiate a signer that wasn't passed to to the #[derive(Accounts)] struct and I can't pass it because only the program can sign with this key.

Is there a way to do CPIs to the same program? Can I instantiate a Signer?

Answer 1

You can do self-reentrancy in a Solana program, but perhaps there are some gotchas when using it with Anchor: https://docs.solana.com/developing/programming-model/calling-between-programs#reentrancy

This does count as a CPI since you're issuing another instruction to your same program.

However, it seems like you might be better served by refactoring your logic to call into some helper function, ie:

#[program]
pub mod dippies_index_protocol {
    use super::*;

    pub fn foo(
        ctx: Context<Foo>,
    ) -> Result<()> {
        do_bar(ctx)
    }

    pub fn bar(
        ctx: Context<Bar>,
    ) -> Result<()> {
        do_bar(ctx)
    }
}

fn do_bar() -> Result<()> {
    Ok(())
}