statem: add gen_statem! authoring macro (RFC 017 chunk 1)
Declarative macro_rules! that fuses the hand-written statem surface into
one invocation: emits the unified event enum, the machine struct + state
cell, start, the Machine impl (dispatch + stay/transition apply-tail), and
the enter dispatch. User keeps the meaningful types, the per-state
successor enums, and the free handler fns.
Pure sugar: every safety property is a property of the emitted code,
checked by rustc, so a declarative macro carries (almost) the proc-macro
guarantee set:
1. forgotten (state,event) pair -> E0004 (total match, no injected _)
2. conflicting row -> unreachable_patterns (macro self-denies; HARD only
in-crate, suppressed cross-crate by in_external_macro -- documented)
3. orphan handler -> dead_code (handlers are user free fns)
4. out-of-set target -> E0599 (per-state successor enums)
Hygiene: bodies can't see the macro's self/cx, so the caller names them
via `context(data, prev, cx)` (shared call-site hygiene).
No separate transitions{} block: the match IS the table, successor enums
ARE the per-state target sets (fused variant, diverges from RFC
edge-lint).
- examples/statem_macro.rs: Door machine via the macro (parallel to the
hand-written examples/statem_fused.rs; diff the two to see the delta).
- in-crate test exercises a machine + anchors the in-crate #2 guarantee.
This commit is contained in:
smarm-agent
@@ -0,0 +1,236 @@
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//! SPIKE (throwaway) — RFC 017 "fused" approach.
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//!
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//! This is the hand-written *expansion target* of the eventual `statem!` macro,
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//! written out in full so the primitives can be judged standing on their own.
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//! A macro would generate exactly this from a `transitions { … }` block; nothing
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//! here needs the macro to be correct or safe.
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//!
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//! The design, as settled over the prior iterations:
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//!
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//! * States and events are real enums. An invalid state is unrepresentable;
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//! there are no bitflags, no `u32` superpositions, no unsafe unions.
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//!
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//! * The dispatch `match (state, event)` IS the transition table. It is
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//! *total* — no catch-all `_` arm — so:
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//! - a forgotten (state, event) pair is a non-exhaustive `match` (E0004),
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//! - a duplicated/conflicting row is `unreachable_patterns` (denied below).
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//!
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//! * Single-target rows name their target in the table; the handler (if any)
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//! is side-effect-only. The table owns the target, so it cannot be wrong.
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//!
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//! * Branching rows have the handler return a per-row *successor enum*. A
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//! target outside that enum is E0599; a missing one is E0004. (See
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//! `UnlockOutcome` and `on_unlock`.)
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//!
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//! * Handlers are module-private. The only way to reach one is through the
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//! actor's message interface via this table, so a handler that is never
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//! wired in is dead code — and dead_code is denied below, making an orphan
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//! handler a compile error.
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//!
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//! * Drops onto the committed `Machine` / `Resolution` / `Cx` primitives with
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//! no change to `src/statem.rs`.
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//!
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//! Default build is clean and runs. A BREAK-CASE MENU at the bottom documents
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//! how to make each of the four guarantees fire.
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//!
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//! Run: `cargo run --example statem_fused`
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#![deny(dead_code, unreachable_patterns)]
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use smarm::run;
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use smarm::statem::{spawn, Cx, Machine, Reply, Resolution, StatemRef};
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// === user types ============================================================
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#[derive(Clone, Copy, PartialEq, Eq, Debug)]
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enum Door {
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Open,
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Closed,
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Locked,
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}
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struct Data {
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enters: u32, // total state entries (incl. initial)
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pushes: u32, // times a push closed the door
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}
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enum Cast {
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Push,
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Pull,
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Lock,
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Unlock(u32), // carries a key
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}
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enum Call {
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GetState(Reply<Door>),
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GetEnters(Reply<u32>),
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GetPushes(Reply<u32>),
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}
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enum Ev {
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Cast(Cast),
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Call(Call),
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}
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const CODE: u32 = 1234;
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// === per-row successor enum for the one branching row ======================
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// `Locked + Unlock` may end in Closed (right key) or Locked (wrong key) — and
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// nothing else. This type IS that declared set; `on_unlock` cannot name Open.
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enum UnlockOutcome {
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Closed,
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Locked,
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}
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impl From<UnlockOutcome> for Door {
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fn from(o: UnlockOutcome) -> Door {
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match o {
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UnlockOutcome::Closed => Door::Closed,
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UnlockOutcome::Locked => Door::Locked,
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}
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}
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}
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// === module-private handlers (side effects / branch choice only) ===========
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// Reachable solely through the table below. Orphan one and it is dead_code.
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fn on_push(data: &mut Data) {
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data.pushes += 1;
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}
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fn on_unlock(key: u32) -> UnlockOutcome {
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if key == CODE {
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UnlockOutcome::Closed
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} else {
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UnlockOutcome::Locked // wrong key: caller will see this == current -> stay
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}
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}
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// === the machine ===========================================================
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struct DoorSm {
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state: Door,
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data: Data,
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}
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impl DoorSm {
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fn start(init: Door) -> StatemRef<DoorSm> {
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spawn(DoorSm {
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state: init,
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data: Data { enters: 0, pushes: 0 },
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})
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}
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fn enter(&mut self, _cx: &mut Cx<Ev>) {
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self.data.enters += 1;
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}
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}
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impl Machine for DoorSm {
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type Ev = Ev;
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fn on_start(&mut self, cx: &mut Cx<Ev>) {
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self.enter(cx);
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}
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fn handle(&mut self, ev: Ev, cx: &mut Cx<Ev>) {
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let prev = self.state;
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// ---- the transition table -----------------------------------------
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// This match is total over (Door, Ev). Read it as the declared graph:
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// each `=> To(x)` is an edge, each `=> Unhandled` an explicit refusal.
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let res: Resolution<Door> = match (self.state, ev) {
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// --- Open -------------------------------------------------------
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(Door::Open, Ev::Cast(Cast::Push)) => {
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on_push(&mut self.data);
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Resolution::To(Door::Closed)
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}
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(Door::Open, Ev::Cast(Cast::Pull | Cast::Lock | Cast::Unlock(_))) => {
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Resolution::Unhandled
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}
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// --- Closed -----------------------------------------------------
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(Door::Closed, Ev::Cast(Cast::Pull)) => Resolution::To(Door::Open),
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(Door::Closed, Ev::Cast(Cast::Lock)) => Resolution::To(Door::Locked),
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(Door::Closed, Ev::Cast(Cast::Push | Cast::Unlock(_))) => Resolution::Unhandled,
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// --- Locked (branching row: handler picks within UnlockOutcome) -
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(Door::Locked, Ev::Cast(Cast::Unlock(key))) => {
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Resolution::To(on_unlock(key).into())
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}
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(Door::Locked, Ev::Cast(Cast::Push | Cast::Pull | Cast::Lock)) => {
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Resolution::Unhandled
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}
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// --- state-independent queries (reply, then stay) ---------------
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(_, Ev::Call(Call::GetState(r))) => {
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r.reply(prev);
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Resolution::To(prev)
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}
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(_, Ev::Call(Call::GetEnters(r))) => {
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r.reply(self.data.enters);
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Resolution::To(prev)
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}
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(_, Ev::Call(Call::GetPushes(r))) => {
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r.reply(self.data.pushes);
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Resolution::To(prev)
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}
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};
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// ---- apply the resolution -----------------------------------------
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match res {
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Resolution::To(s) if s == prev => {} // stay: no enter
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Resolution::To(s) => {
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self.state = s; // sole writer of the state cell
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self.enter(cx);
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}
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Resolution::Postpone => unreachable!("postpone lands in chunk 3"),
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Resolution::Unhandled => cx.on_unhandled(),
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}
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}
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}
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fn main() {
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run(|| {
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let door = DoorSm::start(Door::Closed);
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door.send(Ev::Cast(Cast::Lock)).unwrap(); // Closed -> Locked
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door.send(Ev::Cast(Cast::Push)).unwrap(); // Locked: Push invalid -> Unhandled
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door.send(Ev::Cast(Cast::Unlock(0))).unwrap(); // Locked: wrong key -> stay
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door.send(Ev::Cast(Cast::Unlock(CODE))).unwrap(); // Locked -> Closed
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door.send(Ev::Cast(Cast::Pull)).unwrap(); // Closed -> Open
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door.send(Ev::Cast(Cast::Push)).unwrap(); // Open -> Closed (pushes=1)
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let st = door.call(|r| Ev::Call(Call::GetState(r))).unwrap();
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let enters = door.call(|r| Ev::Call(Call::GetEnters(r))).unwrap();
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let pushes = door.call(|r| Ev::Call(Call::GetPushes(r))).unwrap();
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println!("state={st:?} enters={enters} pushes={pushes}");
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assert_eq!(st, Door::Closed);
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assert_eq!(enters, 5); // Closed(start) + Locked + Closed + Open + Closed
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assert_eq!(pushes, 1);
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println!("ok");
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});
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}
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// ===========================================================================
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// BREAK-CASE MENU — each makes one compile-time guarantee fire.
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//
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// 1. ORPHAN HANDLER (dead_code -> error):
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// add `fn on_slam(_d: &mut Data) {}` and don't reference it.
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// => error: function `on_slam` is never used
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//
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// 2. CONFLICTING ROW (unreachable_patterns -> error):
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// duplicate an arm, e.g. add a second
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// `(Door::Open, Ev::Cast(Cast::Push)) => Resolution::Unhandled,`
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// => error: unreachable pattern
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//
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// 3. MISSING PAIR (non-exhaustive match, E0004):
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// delete the `(Door::Locked, Ev::Cast(Cast::Push | Cast::Pull | Cast::Lock))`
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// arm.
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// => error[E0004]: non-exhaustive patterns: ... not covered
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//
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// 4. OUT-OF-SET TARGET (E0599):
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// in `on_unlock`, return `UnlockOutcome::Open`.
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// => error[E0599]: no variant ... named `Open` found for enum `UnlockOutcome`
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// ===========================================================================
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@@ -0,0 +1,171 @@
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//! RFC 017 — the **same** machine as `examples/statem_fused.rs`, written through
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//! the `gen_statem!` macro. Diff this file against that one to see exactly what
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//! the macro buys: every `// ===` section there that was boilerplate (the `Ev`
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//! enum, the `DoorSm` struct, `start`, the whole `Machine` impl, the `enter`
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//! dispatch, the stay/transition apply-tail) collapses into the invocation
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//! below. What stays hand-written is what carries meaning: the four types, the
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//! per-state successor enum, and the handler fns.
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//!
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//! The point of the exercise is that the macro is *pure sugar*: the four
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//! compile-time guarantees the fused spike demonstrates are properties of the
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//! emitted code, not of the macro, so they survive expansion unchanged. The
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//! BREAK-CASE MENU at the bottom is the same four cases, re-expressed against
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//! the macro surface — flip any one on and the compiler fires identically.
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//!
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//! Run: `cargo run --example statem_macro`
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#![deny(dead_code)] // guarantee #3 (orphan handlers); the macro denies the
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// dispatch's own unreachable_patterns internally.
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use smarm::gen_statem;
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use smarm::run;
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use smarm::statem::Reply;
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// === user types (identical to statem_fused.rs) =============================
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#[derive(Clone, Copy, PartialEq, Eq, Debug)]
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enum Door {
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Open,
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Closed,
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Locked,
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}
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struct Data {
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enters: u32, // total state entries (incl. initial)
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pushes: u32, // times a push closed the door
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}
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enum Cast {
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Push,
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Pull,
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Lock,
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Unlock(u32), // carries a key
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}
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enum Call {
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GetState(Reply<Door>),
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GetEnters(Reply<u32>),
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GetPushes(Reply<u32>),
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}
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const CODE: u32 = 1234;
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// === per-row successor enum for the one branching row ======================
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// `Locked + Unlock` may end in Closed (right key) or Locked (wrong key) — and
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// nothing else. This type IS that declared set; `on_unlock` cannot name Open.
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enum UnlockOutcome {
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Closed,
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Locked,
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}
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impl From<UnlockOutcome> for Door {
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fn from(o: UnlockOutcome) -> Door {
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match o {
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UnlockOutcome::Closed => Door::Closed,
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UnlockOutcome::Locked => Door::Locked,
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}
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}
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}
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// === module-private handlers (side effects / branch choice only) ===========
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// Reachable solely through the table below. Orphan one and it is dead_code.
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fn on_push(data: &mut Data) {
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data.pushes += 1;
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}
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fn on_unlock(key: u32) -> UnlockOutcome {
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if key == CODE {
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UnlockOutcome::Closed
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} else {
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UnlockOutcome::Locked // wrong key: caller will see this == current -> stay
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}
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}
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// === the machine ===========================================================
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// Everything below — Ev, DoorSm, start, Machine, enter — is generated.
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gen_statem! {
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machine: DoorSm { state: Door, data: Data };
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event: Ev { cast: Cast, call: Call };
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// You name the bindings the bodies use; the macro can't lend you its own
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// `self`/`cx` across macro hygiene. `data` = &mut Data, `prev` = current
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// state tag, `cx` = context handle (unused in chunk 1).
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context(data, prev, cx);
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enter {
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_ => data.enters += 1,
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}
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on Door::Open => {
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cast Cast::Push => { on_push(data); Door::Closed },
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cast Cast::Pull | Cast::Lock | Cast::Unlock(_) => unhandled,
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}
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on Door::Closed => {
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cast Cast::Pull => Door::Open,
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cast Cast::Lock => Door::Locked,
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cast Cast::Push | Cast::Unlock(_) => unhandled,
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}
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on Door::Locked => {
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cast Cast::Unlock(key) => on_unlock(key), // branch -> UnlockOutcome
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cast Cast::Push | Cast::Pull | Cast::Lock => unhandled,
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}
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// state-independent queries (reply, then stay via `prev`)
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on _ => {
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call Call::GetState(r) => { r.reply(prev); prev },
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call Call::GetEnters(r) => { r.reply(data.enters); prev },
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call Call::GetPushes(r) => { r.reply(data.pushes); prev },
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}
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}
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fn main() {
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run(|| {
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let door = DoorSm::start(Door::Closed, Data { enters: 0, pushes: 0 });
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door.send(Ev::Cast(Cast::Lock)).unwrap(); // Closed -> Locked
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door.send(Ev::Cast(Cast::Push)).unwrap(); // Locked: Push invalid -> Unhandled
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door.send(Ev::Cast(Cast::Unlock(0))).unwrap(); // Locked: wrong key -> stay
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door.send(Ev::Cast(Cast::Unlock(CODE))).unwrap(); // Locked -> Closed
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door.send(Ev::Cast(Cast::Pull)).unwrap(); // Closed -> Open
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door.send(Ev::Cast(Cast::Push)).unwrap(); // Open -> Closed (pushes=1)
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let st = door.call(|r| Ev::Call(Call::GetState(r))).unwrap();
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let enters = door.call(|r| Ev::Call(Call::GetEnters(r))).unwrap();
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let pushes = door.call(|r| Ev::Call(Call::GetPushes(r))).unwrap();
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println!("state={st:?} enters={enters} pushes={pushes}");
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assert_eq!(st, Door::Closed);
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assert_eq!(enters, 5); // Closed(start) + Locked + Closed + Open + Closed
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assert_eq!(pushes, 1);
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println!("ok");
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});
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}
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// ===========================================================================
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// BREAK-CASE MENU — the four guarantees, through the macro. Each fires exactly
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// as it does in the hand-written statem_fused.rs.
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//
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// 1. ORPHAN HANDLER (dead_code -> error):
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// add `fn on_slam(_d: &mut Data) {}` and don't reference it.
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// => error: function `on_slam` is never used
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//
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// 2. CONFLICTING ROW (unreachable_patterns):
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// duplicate a row, e.g. add a second
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// `cast Cast::Push => unhandled,` under `on Door::Open`.
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// NOTE: this example is a separate crate from `smarm`, so rustc's
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// in_external_macro rule SILENCES this lint here even though the macro
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// denies it — the duplicate compiles. The guarantee is real only for
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// machines defined inside the smarm crate (see the unit test in
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// src/statem.rs). This is the documented macro_rules! limitation.
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//
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// 3. MISSING PAIR (non-exhaustive match, E0004):
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// delete the `cast Cast::Push | Cast::Pull | Cast::Lock => unhandled,`
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// row under `on Door::Locked`.
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// => error[E0004]: non-exhaustive patterns: ... not covered
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//
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// 4. OUT-OF-SET TARGET (E0599):
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// in `on_unlock`, return `UnlockOutcome::Open`.
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// => error[E0599]: no variant ... named `Open` found for enum `UnlockOutcome`
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// ===========================================================================
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Reference in New Issue
Block a user