Attribute Macro migration 

#[migration]

Attribute macro that wraps a migration function into a MigrationStep.

The function must take a single argument (the old version’s data) and return the new version’s data. Both types must implement Serialize and DeserializeOwned.

Attributes

• from = N — Required. Source schema version.
• to = M — Required. Target schema version.

Generated Code

Creates a struct {FnName}Migration that implements MigrationStep. The struct handles deserialization of the old format, calls your function, and serializes the result.

Also generates a register_{fn_name} function that returns a boxed MigrationStep for convenient registration.

Example

use crdt_migrate_macros::migration;
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize)]
struct SensorV1 { temperature: f32 }

#[derive(Serialize, Deserialize)]
struct SensorV2 { temperature: f32, humidity: Option<f32> }

#[migration(from = 1, to = 2)]
fn add_humidity(old: SensorV1) -> SensorV2 {
    SensorV2 {
        temperature: old.temperature,
        humidity: None,
    }
}
// Generates: AddHumidityMigration struct + impl MigrationStep
// Generates: fn register_add_humidity() -> Box<dyn MigrationStep>