initial commit: hsmc v0.2 with during: activities

Hierarchical statechart codegen for Rust with:
- during: activities for state-scoped concurrent I/O
- field-list borrowing (split-borrow inside the run loop)
- embassy-first async with tokio support
- STATE_CHART const for tooling/inspection
- examples: microwave, microwave_tui, embassy_full, during_radio

hsmc-macros/src/lib.rs

@@ -0,0 +1,29 @@
+//! Proc-macro backing for the `hsmc` crate. The sole public item is the
+//! [`statechart!`] macro which generates a state machine from a declarative
+//! description.
+
+use proc_macro::TokenStream;
+
+mod parse;
+mod ir;
+mod validate;
+mod codegen;
+
+/// See the `hsmc` crate for documentation.
+#[proc_macro]
+pub fn statechart(input: TokenStream) -> TokenStream {
+    let input = proc_macro2::TokenStream::from(input);
+    match statechart_impl(input) {
+        Ok(ts) => ts.into(),
+        Err(e) => e.to_compile_error().into(),
+    }
+}
+
+fn statechart_impl(input: proc_macro2::TokenStream) -> syn::Result<proc_macro2::TokenStream> {
+    let parsed = syn::parse2::<parse::StatechartInput>(input)?;
+    validate::validate_parse_tree(&parsed)?;
+    let mut ir = ir::build_ir(parsed)?;
+    ir::resolve_transitions(&mut ir)?;
+    validate::validate(&ir)?;
+    Ok(codegen::generate(&ir))
+}