Versioned

Schema migrations for persisted files.

Every persisted struct carries a version: u32 (via Versioned). Migrator<T> holds an ordered set of from_version → from_version + 1 transformations expressed on raw toml::Value — pre-deserialization, so a v1 file that no longer matches the v2 type can still be upgraded.

use teksilo_settings::{Versioned, Migrator};
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, Debug, PartialEq, Default)]
struct Recents {
    version: u32,
    items: Vec<Entry>,
}

#[derive(Serialize, Deserialize, Debug, PartialEq)]
struct Entry { path: String, pinned: bool }

impl Versioned for Recents {
    const CURRENT_VERSION: u32 = 2;
    fn version(&self) -> u32 { self.version }
    fn set_version(&mut self, v: u32) { self.version = v; }
}

// v1 didn't have `pinned`; supply false.
let migrator: Migrator<Recents> = Migrator::new()
    .step(1, |mut v| {
        if let Some(items) = v.get_mut("items").and_then(|i| i.as_array_mut()) {
            for item in items {
                if let Some(t) = item.as_table_mut() {
                    t.insert("pinned".into(), toml::Value::Boolean(false));
                }
            }
        }
        Ok(v)
    });

Builder methods at a glance

step, run

API reference

📖 Full rustdoc API for this module

pub enum MigrationError

Errors surfaced by Migrator::run.

#![allow(unused)]
fn main() {
pub enum MigrationError { /* variants */ }
}

Variants

• NewerThanCurrent — The on-disk version number exceeds T::CURRENT_VERSION; the file was written by a newer build and cannot be read safely.
• NoStepFor — The chain is missing a step for the encountered version, making it impossible to reach T::CURRENT_VERSION.
• Step — A migration step closure returned Err(message).
• Deserialize — The migrated toml::Value did not deserialize as T.

pub struct Migrator

Schema migration pipeline for a Versioned type.

Add from → from + 1 steps with Migrator::step; the order in which they're added does not matter — Migrator::run walks them in version order.

Migrator<T> is cheaply Clone (each step's closure lives behind an Arc, so cloning is a handful of refcount bumps, not a deep copy) and Send + Sync whenever T is — which is what lets a Patch (crate::flush::Patch) closure retain its own copy of the migrator and re-run it against the document read fresh on the shared I/O worker thread, instead of the stale, possibly-out-of-date value this handle loaded at construction.

#![allow(unused)]
fn main() {
pub struct Migrator<T: Versioned + DeserializeOwned> { /* fields */ }
}

Methods

pub fn new() -> Self

Create an empty migrator with no steps registered.

If T::CURRENT_VERSION is 1 (the initial schema) or the file is already at the current version, no steps are needed and run will succeed immediately.

pub fn step<F>(mut self, from: u32, func: F) -> Self where F: Fn(toml::Value) -> Result<toml::Value, String> + Send + Sync + 'static,

Register a step that promotes a value from from to from + 1. Steps may be registered in any order; run finds the right one for the current version on demand.

pub fn run(&self, mut raw: toml::Value) -> Result<T, MigrationError>

Migrate raw from its on-disk version up to T::CURRENT_VERSION, then deserialize.

Reads the version directly from the version field of the raw toml::Value — never deserializes-then-checks, because a v1 payload typically fails to deserialize as the v2 type.

Files missing the version field are treated as v1 (legacy).