# Changelog All notable changes to this workspace are documented here. The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/) and this project adheres to [Semantic Versioning](https://semver.org/). ## 0.5.1 — 2026-04-29 Docs and licensing cleanup. No code or behavior changes. - **License simplified to MIT.** The crate was previously dual-licensed MIT OR Apache-2.0; it is now MIT-only. `LICENSE-APACHE` removed, `LICENSE-MIT` renamed to `LICENSE`, workspace `license` field is now `"MIT"`. Copyright (c) 2026 Stephen Waits <steve@waits.net>. - **README rewritten reader-first.** Restructured top-to-bottom so a reader who's never used statecharts can follow the document linearly: a working Blinker chart is now the first concrete artifact; the Quickstart sits directly under it; the larger Radio example (events / payloads / `during:`) follows; the formal eight-rule semantics live below all of that as reference rather than as a prerequisite. The "What it does" feature list is rewritten in user-benefit-first language. The "What `hsmc` deliberately does NOT have" table is promoted from a sub-section to its own top-level section. No semantic changes — the formal rules' content is untouched, only repositioned. - **Tokio integration story corrected.** The README previously implied driving a chart under tokio required `tokio::task::LocalSet`. The normal path is `#[tokio::main(flavor = "current_thread")]` — one line, no extra wrapping, and how the existing examples have always worked. `LocalSet` no longer appears in the README at all. - **`microwave_tui` example dropped.** The ratatui/crossterm TUI variant of the microwave was overkill for a library example and pulled in three dev-dependencies (`ratatui`, `crossterm`, `futures`) that nothing else used. The `microwave` example covers the same feature surface in plain Rust. - **Observability framed honestly.** Enabling `defmt` / `log` / `tracing` output for a chart is one `trace-*` Cargo feature on hsmc's side, plus whatever your downstream crate already does to init its logger (e.g. `tracing_subscriber::fmt::init()` or `env_logger::init()`) — hsmc deliberately doesn't init a logger, per the standard Rust library convention. The Observability section now says so directly and includes a runnable end-to-end snippet using `tracing-subscriber`. The `trace-*` features are also listed in the main feature-flags table so they're discoverable at a glance. - **Inline examples corrected.** The Quickstart Blinker now has both `light_on` and `light_off` actions (it previously had only `light_on`, which left the LED on the whole time). The Embassy snippet no longer declares an unused event channel for what is a timer-only chart. - **Eight-rule order finalized.** The "How a chart behaves" rules are now strictly bottom-up: active path → transitions (LCA-aware) → up-transition rule → entry/exit ordering → `default(...)` (a transition fired on entry) → event bubbling → timers → emit/during/termination. Cross-references updated. ## 0.5.0 — 2026-04-28 ### `default(...)` is a real LCA-aware transition `default(...)` is now modeled the same way as any event-driven transition. It fires immediately after the declaring state's entries finish and its durings start, applying the standard exit-to-LCA / enter-to-target algorithm. Three behavioral changes follow from this: - **Optional.** A state with children no longer must declare a `default(...)`. When omitted, the state itself is the resting innermost active state; substates are reachable only via explicit transitions. This is the "microwave Standby" pattern — `Standby` has substates like `LowPower` you enter only on demand, and `=> Standby;` lands at `Standby` itself with no descent. - **Targets anywhere.** The default target may be any state in the chart — a child (the classic descent case), a sibling, an ancestor, anywhere. `default()` exits the just-entered state as part of the default-fire transition; the same uniform rule covers descent, redirection, and up-bounce. - **Cycle-checked at compile time.** The default-edge graph (out-degree ≤ 1 per node) is rejected if it contains any cycle, including `default(self)`. The check guarantees default chains terminate at runtime — entering any state in a cycle would loop forever before reaching user code. ### Breaking changes - **Journal format.** Default-fires now emit `TransitionFired` (with `reason: TransitionReason::Internal`) and `TransitionComplete` brackets around their entry sequence. `Internal` was previously reserved and never emitted; it is now active. Charts that hand-build expected journal sequences (replay-style tests) must include these brackets around every default-fire — see the per-test diffs in this release for the pattern. - **Validation.** Two compile-time errors went away: `default()` is now valid (the target may be anywhere), and `default` on a childless state is now valid (the leaf transitions out immediately on entry). Code relying on these as guard rails must adapt. A new compile-time error takes their place: any cycle in the default graph is rejected with a pinpoint message naming the cycle (e.g. `default-transition cycle detected: A -> B -> A`). ### Other - README and `docs/002. hsmc-semantics-formal.md` rewritten so the default-as-transition framing is the primary description; the old "automatic transition into a child" language is gone. - New integration tests covering each branch of the new semantics: `det_optional_default` (microwave pattern), `det_default_sibling` (lateral default), `det_default_chained` (multi-link default chain), `det_default_ancestor` (up-default landing on an ancestor). - New compile-fail UI fixtures for cycle detection (`t9_4_default_self_cycle`, `t9_5_default_two_cycle`) and new compile-pass fixtures for non-child default targets (`composite_without_default`, `default_targets_sibling`, `default_targets_ancestor`). ## 0.4.1 — 2026-04-28 ### Performance — dispatch hot path Six codegen-side optimization passes against `step()` and friends. No user-facing API changes; all 296 tests pass under `--no-default-features`, `--features tokio`, `--features embassy`, and `--features tokio,journal`. Cumulative on `h8_cross_tree` (the deepest dispatch in the bench suite): **−82% instructions / −72% cycles** vs the pre-`pre_lca_fix` baseline. See `hsmc/benches/baseline.txt` for per-pass delta blocks and `docs/003. latency-analysis.md` §1/§9/§12 for the cost-surface analysis. - **Precomputed transition paths.** For every `(from, to)` state pair, codegen materializes the exit/enter sequence into a single flat `__PATH_DATA` blob with a `__PATH_RANGE: [(u16, u16, u16); N²]` index. `transition()` becomes one indexed range lookup + two slice loops; the `lca()` runtime helper, `is_up_transition()`, and the per-call `heapless::Vec` ancestry build are gone. Up / self / lateral semantics are baked into the table (empty enter slice ⇒ up-transition, target excluded; non-empty enter slice includes the default-descent tail). Hierarchy depth is no longer bounded by the old 32-state Vec capacity. - **Precomputed event-dispatch table.** For every `(state, event)` pair, codegen resolves the handler the runtime `__PARENT` bubble walk would have found. `__DISPATCH: [(u16, &'static [u16], Option); N×E]` stores `(handler_state, action_ids, transition_target)` per pair; `u16::MAX` in the handler-state slot is the no-handler sentinel. The runtime walk + per-hop `__handler_lookup` call in `step()` collapses to one indexed lookup. Handler resolution is now O(1) regardless of bubble depth — the `bubble_top` bench (4-hop walk) is now within 3 instructions of `bubble_leaf` (handler on current state). `__handler_lookup` is retained for timer dispatch (the `dispatch_trigger` path doesn't bubble). - **Precomputed terminate exit path.** Per-state `__TERMINATE_DATA` table holds the full exit chain up to and including `__Root` (which may carry root-level `entry:`/`exit:` actions). `do_terminate()` indexes the table once and iterates the slice, replacing the runtime `__PARENT` walk + per-iteration match. Queue drain switched from `while pop_front().is_some()` to `Deque::clear()` (heapless 0.8 implements this as O(1) — resets indices instead of popping each entry). `terminate_event` bench: −22.5% instr / −23.4% cycles. - **TimerTable empty-skip.** `pop_expired`, `min_remaining`, `decrement`, and `cancel_state` each get `#[inline]` + an `is_empty()` early-out, with the non-empty body split into a `#[cold]` helper. Runtime branch on charts with timers; the body stays out-of-line. - **Codegen-static timer-machinery elide.** When a chart declares no `Duration` triggers (the common case for event-driven HSMs), every `TimerTable` call is omitted from `step()` and `exit_state()` at codegen. `step()` returns `None` directly for the next-tick deadline. `dispatch_trigger()` and the timer-fired arms remain in the binary but are unreachable; LLVM DCEs them. - **`TimerEntry.remaining_ns: u128 → u64`.** Internal-only field type change. u64 nanoseconds bounds at ~584 years — comfortably past any realistic `Duration`. Eliminates u128 saturating-sub in `decrement()` (4–6 instructions per entry → 1–2) and the manual secs/nanos decomposition in `min_remaining()` (replaced with `Duration::from_nanos`). The struct shrinks 32 B → 16 B with alignment, so the entire machine struct gets smaller — every bench's RAM-hit count drops from tighter cache packing. ### Bench coverage Four new benches added to cover hot paths the original suite missed: - **`bubble_leaf` / `bubble_mid` / `bubble_top`** — handler resolution at varying ancestor depths (0 / 3 / 4 hops) on a single chart. Quantifies the bubble-walk cost as a function of distance, and confirms the `__DISPATCH` table makes resolution depth-independent. - **`timer_fire_dispatch`** — only bench that exercises `pop_expired`'s non-empty branch and `dispatch_trigger`. The most expensive single-step bench in the suite (191 instr / 706 cycles). - **`terminate_event`** — only bench exercising `__check_terminate`'s true arm and `do_terminate`. 69 instr / 311 cycles. - **`bubble_cross_tree`** — handler on L1 (4 bubble hops up from current=L5) targets R5 in a sibling subtree (10-state cross-tree transition). Realistic HSM worst case; 94 instr / 444 cycles — almost the same as a plain 7-deep cross-tree because both bubble resolution and transition path are now O(1) lookups. ## 0.4.0 — 2026-04-28 ### Changed — observability (breaking) - **Unified observation pipeline.** The codegen now emits a single `__chart_observe!` invocation per observable atom, dispatched at compile time to whichever sinks are enabled: the in-memory journal (`feature = "journal"`), `defmt` (`trace-defmt`), `log` (`trace-log`), and/or `tracing` (`trace-tracing`). All sinks share the same vocabulary by construction — the journal IS the observation stream; trace backends are textual renderings of it. With NO sink feature on, every call site expands to `()` (zero overhead). Multiple trace sinks may now be enabled simultaneously (previously they were mutually exclusive). - **Trace prefix changed.** `[ChartName] verb …` → `[statechart:ChartName] verb …`. The new form is greppable and unambiguous in mixed log streams. - **Trace format is now logfmt-style.** Every line is `[statechart:Name] key=value key=value …` (or native structured fields under `tracing`). Twenty verbs cover every TraceEvent variant — entries, exits (with begin/end pairs), actions (with kind), durings, transitions (with **reason** showing what triggered them), events (received/delivered/dropped/queued/failed), timers, terminate. - **`trace;` keyword deprecated.** Still parsed for backwards compatibility, but no longer gates emission. Trace output is now controlled purely by which `trace-*` cargo feature you enable. ### Changed — journal (breaking) - **`TraceEvent::TransitionFired` carries `reason: TransitionReason`.** Replay consumers now see whether a transition was driven by an event (`Event { event: u16 }`), a timer (`Timer { state, timer }`), or internal logic (`Internal`). - **New TraceEvent variants for phase begin/end pairing.** - `EnterBegan { state }` fires before a state's entry actions / timers / durings; `Entered` keeps its place as the end marker. - `ExitBegan { state }` fires before a state's during cancellations / timer cancellations / exit actions; `Exited` keeps its place as the end marker. - `TransitionComplete { from, to }` fires after a transition's full exit-then-enter sequence finishes; pairs with `TransitionFired`. - `EventReceived { event }` fires when an event is popped from the queue, before handler search; pairs with `EventDelivered` / `EventDropped` / `TerminateRequested`. ### Added - **`hsmc/tests/trace_format.rs`** — 11 tests pinning every verb's exact textual rendering, including a journal/trace atom-count equivalence test. - **`TransitionReason`** enum — re-exported from the crate root when `feature = "journal"` is on. Carried on `TraceEvent::TransitionFired`. - **Multiple trace backends compose.** Previously enabling more than one of `trace-defmt` / `trace-log` / `trace-tracing` was a compile error. Now they fan out independently. ### Migration Chart syntax is unchanged: every v0.1 / v0.2 / v0.3 statechart compiles under v0.4 without modification. Breakage is confined to the observability surface area: 1. **Trace line prefix.** Update grep patterns and log filters from `[ChartName]` to `[statechart:ChartName]`. The verb after the prefix is now a single hyphenated token followed by `key=value` pairs. 2. **`TraceEvent::TransitionFired`** has a new `reason` field. Update pattern matches: ```rust // before: TraceEvent::TransitionFired { from, to } => … // after: TraceEvent::TransitionFired { from, to, reason } => … // or, if you don't care: TraceEvent::TransitionFired { from, to, .. } => … ``` 3. **New `TraceEvent` variants.** If you `match` exhaustively, add arms for `EnterBegan`, `ExitBegan`, `TransitionComplete`, `EventReceived`. Otherwise nothing changes. 4. **`trace;` keyword is now a no-op.** Charts that declared it still compile. Trace output is now controlled purely by which `trace-*` cargo feature you enable. 5. **`__chart_trace!` and `__chart_journal!` macros are removed.** These were doc-hidden and not part of the public API; mentioned here for codebases that grepped through the macro emission for patches/forks. ## 0.3.0 — 2026-04-27 ### Added - **`journal` Cargo feature.** Records every observable atom of chart execution — `Started`, `Entered`, `Exited`, `ActionInvoked` (`Entry`/`Exit`/`Handler`), `DuringStarted`, `DuringCancelled`, `TransitionFired`, `EventDelivered`, `EventDropped`, `EmitQueued`, `EmitFailed`, `TimerArmed`, `TimerCancelled`, `TimerFired`, `TerminateRequested`, `Terminated` — into a `Vec` on the generated machine. Same chart + same events = byte-identical journal. Public API: `journal()`, `take_journal()`, `clear_journal()`, `CHART_HASH` (a stable FNV-1a fingerprint of the chart's structural definition). - **Root state targetable by chart name.** `on(Trig) => MyChart;` resolves to the root state in both `classify_target` and `resolve_transitions`. From any nested state this is an up-transition (root is always on the active path). - **113 deterministic-flow tests** (under `--features tokio,journal`) comparing hand-built expected journals byte-for-byte against actual, anchored to spec sections: initial entry, lateral / self / up transitions, default-descent, event bubbling, timer arm / cancel / fire, emit, ordering, durings, step-vs-dispatch equivalence, root-targeting, `current_state()`, termination. - **`verification/` workspace member with Creusot proofs.** Verified mirrors of the runtime `EventQueue` and `TimerTable` carry `creusot-std` (Pearlite) contracts that Why3 + alt-ergo + z3 discharge mechanically. 14/14 VCs proven. `just verify` is self-installing (mise pulls opam + the pinned nightly + Creusot's canonical `INSTALL`). - **`docs/002. hsmc-semantics-formal.md`** — canonical, unambiguous reference for chart behavior. Numbered S-rules supersede the v0.1 prose spec and v0.2 design-change-request. - **README "How a chart behaves" section** — eight building-block rules that build on each other, with an explicit "what hsmc deliberately does NOT have" table. ### Tooling - `mise.toml` (root) declares stable Rust + components + embedded targets + cargo subcommands. `verification/mise.toml` declares the pinned `nightly-2025-11-13` + opam + python venv + uv. - `set shell` and `set script-interpreter` route every `just` recipe through `mise exec` — no shebangs, no per-recipe wrappers. - `just verify` runs `cargo creusot prove --no-cache` so SMT invocations happen on every run; `time` shows ~7s CPU on ~1.2s wall = real parallel work. - `just mutants` runs with `--features tokio,journal` so `journal_*` and `det_*` tests execute. **0 missed mutants.** - `just miri` excludes `hsmc-macros` (trybuild glob hits Miri's isolation) and `hsmc-verification` (different pinned toolchain). 66 tests pass under Miri, 0 UB. ### Backward compatibility Every v0.1 / v0.2 statechart compiles under v0.3 unchanged. ## 0.2.0 — 2026-04-22 ### Fixed — behavior-visible (breaking) - **Up-transitions no longer exit and re-enter the target ancestor.** A transition whose target is already active (i.e., the target is on the path from root to the innermost active state, and the target is not itself the innermost) now unwinds only the subtree strictly below the target. The target's `exit:` / `entry:` actions do NOT fire, and its `default(...)` does NOT re-descend. You cannot re-enter a state you never left. The old semantics (exit target, re-enter, re-descend to default) was incorrect and could produce infinite re-entry when a child transitioned to its own parent. See spec §2.6, §T2.8, §T2.8b, §T2.8c. - Self-transitions (`target == innermost`) are unchanged: the target is still exited and re-entered, timers still restart. - Lateral transitions (target not on the active path) are unchanged. - `current_state()` may now return a composite state when it became innermost via an up-transition. ## 0.1.0 — 2026-04-22 Initial release. ### Added - `statechart!` proc macro: declarative Harel-style hierarchical state machines with nested states, `entry:` / `exit:` actions, LCA-aware transitions, default-child descent, and `terminate` semantics. - Typed event payload bindings: `on(PacketRx { rssi: i16 }) => handler;` expands into a typed handler signature, verified at compile time. - Timer triggers: `on(after Duration::from_secs(5)) => Next;` and `on(every Duration::from_millis(100)) => tick;`, tracked in a fixed-capacity `TimerTable`. - `during:` activities (v0.2 semantics): async functions that run while a state is on the active path and produce events. Multiple concurrent durings on a single state borrow disjoint `&mut` slices of the context, enforced by Rust's native split-borrow. - Runtime: `machine.run().await` races active durings, the external event channel, and timer deadlines — one future, cooperative on embassy, multi-threaded on tokio. - Feature gates: `tokio` (std + tokio runtime), `embassy` (no_std + embassy-time / embassy-sync). The two features are mutually exclusive and enforced via `compile_error!`. - `no_std` by default; `std` pulled in only via the `tokio` feature. - `STATE_CHART` const and `dispatch()` helper for introspection. - Workspace: `hsmc` (library) and `hsmc-macros` (proc-macro front-end) both at `0.1.0`. ### Docs - 320-line `README.md` with quickstart, semantics, and examples. - Runnable examples: `microwave` and `during_radio` under tokio, `embassy_full` under embassy. - Behavior, hierarchy, during, timer, and payload-binding test suites (13 integration tests).