A Solana program cannot check whether a PDA exists unless the account is passed in — check data_is_empty()

Code shaped like this cannot be written in a Solana program:

let (pda, _bump) = Pubkey::find_program_address(&[signer.key().as_ref()], ctx.program_id);
if pda.exists() { ... } else { /* create it */ }

find_program_address computes an address, and that is all it does. A program can only see accounts that were declared in the transaction's account list and handed to it as AccountInfos; there is no syscall to look up arbitrary state by address. Deriving a PDA tells you nothing about whether it has been allocated, funded, or written to. This is the account-model consequence that catches people coming from EVM, where any address is readable from any contract.

The workable pattern is to derive the address on the client, always include it in the transaction, and inspect the passed-in account:

- In Anchor, take it as UncheckedAccount<'info> (or AccountInfo) with a seeds/bump constraint so the address is still verified, then branch on account.data_is_empty() or account.lamports() == 0 to distinguish "not created yet" from "already initialized". - If the branch is exactly create-or-use, #[account(init_if_needed, ...)] does it for you — but only enable the init-if-needed Anchor feature deliberately, since it makes reinitialization attacks possible if the handler does not guard already-initialized state. - For genuinely optional accounts, Option<Account<'info, T>> lets the client pass the program id as a placeholder.

The wrong guess costs real time: there is no "read any account" escape hatch, no matter how the code is restructured, so stop looking for one and change the instruction interface instead.

Source: adapted from a Stack Exchange answer by wei1769 (question by PandaPanda), https://solana.stackexchange.com/questions/9546/verify-if-pda-exists-in-program-using-anchor — CC BY-SA 4.0