Struct MigrationOutcome 

pub struct MigrationOutcome {
    pub from: u32,
    pub to: u32,
}

Bring conn’s database up to SCHEMA_VERSION, or fail explaining why not.

Reading user_version before writing is the whole point. The previous implementation re-ran every CREATE … IF NOT EXISTS unconditionally and then stamped the version it had never read, which meant it could not distinguish a fresh file from a foreign one from a database written by a future build — it simply asserted the schema it wanted and hoped. IF NOT EXISTS hides exactly the case that matters: an object that exists with a different definition is silently kept, so a legacy table would survive with none of its constraints while the stamp claimed otherwise. What run did, so a caller can react to the schema having moved.

The one caller that must is Database::open: a SCHEMA_VERSION bump invalidates every snapshot on disk (D-043), and until Wave 4.4 nothing noticed — the first reconstruct after an upgrade skipped every snapshot as incompatible and folded from genesis, correctly and expensively, with the only trace a warn! per skipped file.

Fields

from: u32

The version the file carried on the way in.

to: u32

SCHEMA_VERSION, always — run either reaches it or fails.

Implementations

impl MigrationOutcome

pub fn upgraded(&self) -> bool

Whether an existing database moved between versions.

A fresh file (from == 0) is deliberately not an upgrade. It has no snapshots to invalidate, so there is nothing to re-anchor — and treating it as one made Database::open write a snapshot on every first open, which broke two contracts the suite already pins: an idle database is never anchored, and a handle opened with no cadence writes nothing until close(). Both are worth keeping. open() touching the disk when it was not asked to is surprising in its own right.

Trait Implementations

impl Clone for MigrationOutcome

fn clone(&self) -> MigrationOutcome

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for MigrationOutcome

impl Debug for MigrationOutcome

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for MigrationOutcome

impl PartialEq for MigrationOutcome

fn eq(&self, other: &MigrationOutcome) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for MigrationOutcome