Macro layout_migrations 

macro_rules! layout_migrations {
    ( $layout:ty = [ $( $edge:expr ),+ $(,)? ] $(,)? ) => { ... };
}

Compose a layout’s LayoutMigration::MIGRATIONS chain from a list of #[hopper::migrate]-emitted edge constants.

#[hopper::migrate(from = 1, to = 2)]
pub fn vault_v1_to_v2(body: &mut [u8]) -> ProgramResult { Ok(()) }

hopper::layout_migrations! {
    Vault = [VAULT_V1_TO_V2_EDGE, VAULT_V2_TO_V3_EDGE],
}

Emits impl LayoutMigration for Vault { const MIGRATIONS = .. }. Each list entry must evaluate to a MigrationEdge. typically the <UPPER_SNAKE_FN_NAME>_EDGE constant that #[hopper::migrate] emits alongside each migration function. Chain continuity (every adjacent pair must satisfy a.to_epoch == b.from_epoch) is enforced at runtime by apply_pending_migrations.