hsmc/CHANGELOG.md

Changelog

All notable changes to this workspace are documented here. The format follows Keep a Changelog and this project adheres to Semantic Versioning.

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<u16, 16> 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<u16>); 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] <verb> 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:

   // 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<TraceEvent> 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).