How does Anchor know space needed for an ata when we don't provide space?

Question

For vault_ata_make, how does anchor know how much space is needed since we didn't specify any space at all ?

#[account(
        init,
        payer = maker,
        //Anchor descr is needed because of InitSpace
        space = 8 + Escrow::INIT_SPACE,
        seeds = [b"escrow",maker.key().as_ref(), seed.to_le_bytes().as_ref()],
        bump
    )]
    pub escrow: Account<'info, Escrow>,
    
    #[account(
        init,
        payer =maker,
        associated_token::mint = mint_to_make,
        associated_token::authority = escrow,
    )]
    pub vault_ata_make: InterfaceAccount<'info, TokenAccount>,

Answer 1

Anchor has special constraints for the some SPL token programs. In the case of your vault_ata_make, it's using the Associated Token program (ATP) constraints. Since the init constraint is being used with the ATP constraints, Anchor under the hood invokes the ATP here. Ultimately the ATP determines space needed here.