layoutd gen

Purpose#

layoutd gen writes the migration. It produces a Migration<Old, New> implementation that carries every safe field across unchanged and annotates every dangerous decision so you can’t ship one by accident.

Invocation#

layoutd gen v1.json v2.json --account UserState

The scaffold#

For the UserState example, the inserted is_active field is a DANGER, so gen emits a complete scaffold with that one decision left for you — every other field is wired up automatically.

// layoutd gen  —  account: UserState  [borsh]// WARNING: dangerous changes present — resolve every DANGER line before shippingimpl Migration<OldUserState, UserState> {    pub fn migrate(old: OldUserState) -> UserState {        UserState {            authority: old.authority,            // DANGER: is_active inserted at index 1 — shifts following offsets; supply value            // is_active: todo!("supply value"),            balance: old.balance,            bump: old.bump,        }    }}

How DANGER lines are annotated#

• Each dangerous field becomes a commented // DANGER: … line explaining the consequence, paired with a todo!("supply value") placeholder.
• The scaffold does not compile until you resolve every todo!() — so a dangerous migration can never silently slip through.
• Safe fields (authority, balance, bump) are mapped directly from the old account, with shifted offsets computed for you.

Proof-hash pinning & realloc#

gen pins a proof hash of the exact layouts it analysed, so a later check can confirm the migration still matches the inputs it was generated from. For variable-size accounts, the scaffold includes the realloc and rent-adjustment steps needed when the new layout changes the account’s size.

Once you’ve resolved the todo!() lines, acknowledge the deliberate danger and let layoutd check confirm the upgrade is safe to ship.