Feature flags

Cargo features across the workspace. The engine (xstate-core) has one build feature, fast-path (on by default), and is otherwise the same small, I/O-free crate. Backends and integrations are opt-in so that a program pays, in compile time and dependencies, only for what it uses, which is the same contract as the Python library’s pip install "xstate-statemachine[extra]".

The facade: `xstate-statemachine`

Depend on the facade and pick features; each one enables an optional dependency, adds a module of the same name (xstate_statemachine::tokio, ::persistence, …) and the matching items of xstate_statemachine::prelude. Nothing is enabled by default.

Feature	Enables	Implies	Python extra
`tokio`	`xstate-tokio`: async interpreter, `spawn`, `Interpreter`		core (asyncio engine)
`persistence`	`xstate-persistence`: `StateStore`, memory and file stores, locks, `persisted`, durable timers, inbox, log, migrations		core (persistence)
`sqlite`	`SqliteStore`, `SqliteInbox`, `SqliteLog` (and the SQLite outbox and dead-letter stores of `eda`, if enabled)	`persistence`	core (stdlib `sqlite3`)
`redis`	`RedisStore`, `RedisInbox`, `RedisLog`	`persistence`	`redis`
`postgres`	`PostgresStore`, `PostgresInbox`, `PostgresLog` (sqlx, rustls)	`persistence`	`sqlalchemy`
`eda`	`xstate-eda`: envelope, broker contract, dispatcher, outbox, dead letters, AsyncAPI	`persistence`	`eda`
`redis-streams`	`RedisStreamsBroker`	`eda`	`redis`
`nats`	`NatsBroker` (JetStream)	`eda`	`nats`
`rabbitmq`	`RabbitMqBroker`	`eda`	`rabbitmq`
`sqs`	`SqsBroker`	`eda`	`sqs`
`patterns`	`xstate-patterns`: retry, circuit breaker, saga, choreography	`eda`	core (`patterns`)
`observability`	`xstate-observability`: `MetricsObserver`		`observability`
`inspect`	`xstate-inspect`: Stately Inspector protocol, JSONL, replay, SSE sink		core (`inspect`)
`macros`	`xstate-macros`: `TypedEvent`, `TypedState`, `statechart!`		the Pythonic DSL
`axum`	`xstate-axum`: registry, REST, SSE, WebSocket, inspector endpoint	`persistence`, `inspect`	`starlette`, `fastapi`
`agents`	`xstate-agents`: LLM agents as statecharts		`agents`
`testing`	`xstate-testing` (a skeleton today; see its README)		`testing`
`full`	all of the above		`all`

Examples:

# a service that persists to PostgreSQL and consumes from NATS
xstate-statemachine = { version = "0.1", features = ["tokio", "postgres", "nats", "observability"] }

# a library that only needs the engine: no features
xstate-statemachine = "0.1"

A few points:

sqlite is separate from persistence on purpose: it compiles a bundled copy of SQLite (a C dependency). persistence alone gives the memory and file stores.
The Redis, PostgreSQL and SQS features pull in sizeable dependency trees (redis, sqlx, the AWS SDK); full builds all of them.
Features are additive and unify across a build, like every Cargo feature.

Per-crate features

If you depend on the individual crates, these are all of their features. A crate not listed has none.

`xstate-core`

Feature	Default	Adds
`fast-path`	yes	the single-transition microstep fast path (on unless `default-features = false`)

--no-default-features compiles the fast path out, so every step goes through the general microstep. The conformance suite runs both ways in CI; the two paths are also compared case-by-case by the crate’s own differential tests.

`xstate-persistence`

Feature	Default	Adds	Dependencies
`sqlite`	yes	`SqliteStore`, `SqliteInbox`, `SqliteLog`	`rusqlite` (bundled SQLite)
`redis`	no	`RedisStore`, `RedisInbox`, `RedisLog`	`redis` (tokio, connection manager, scripts)
`postgres`	no	`PostgresStore`, `PostgresInbox`, `PostgresLog`	`sqlx` (rustls, postgres), `tokio`

`xstate-eda`

Feature	Default	Adds	Dependencies
`sqlite`	yes	`SqliteOutboxStore`, `SqliteDeadLetterStore`; also enables `xstate-persistence/sqlite`	`rusqlite`
`redis-streams`	no	`RedisStreamsBroker`	`redis`, `tokio`
`nats`	no	`NatsBroker`	`async-nats`, `futures-util`, `tokio`
`rabbitmq`	no	`RabbitMqBroker`	`lapin`, `tokio`
`sqs`	no	`SqsBroker`	`aws-config`, `aws-sdk-sqs`, `tokio`

xstate-patterns depends on xstate-eda and xstate-persistence with default features off, so it does not drag SQLite in.

Crates without features

xstate-tokio, xstate-testing, xstate-inspect, xstate-observability, xstate-patterns, xstate-macros, xstate-axum, xstate-agents and the xsm binary (package xstate-statemachine-cli). The xstate-conformance (test harness) and xstate-py (Python bindings) crates are not published to crates.io.

TLS and C dependencies

TLS, where a feature has it, is rustls; openssl-sys is banned in deny.toml. sqlite compiles a bundled copy of SQLite, and the rustls backends of postgres, nats, rabbitmq and sqs build ring or aws-lc-sys, so a C compiler is needed on the build machine for those features.

MSRV

The workspace declares Rust 1.88. Every feature builds on 1.88 except postgres (and therefore full, which includes it): sqlx 0.9 requires Rust 1.94, so enabling it needs a toolchain that new. The MSRV job in ci.yml checks the workspace and every other feature on 1.88 and skips postgres; the other jobs run on stable, which covers it.

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