Replaces the iter mut.1 dispatch stubs in synth with real typecheck
logic. Codegen stubs stay (deferred to mut.3); examples/mut.ail now
typechecks clean but still cannot run end-to-end.
Concretely:
- crates/ailang-check/src/lib.rs: three new CheckError variants
(MutAssignOutOfScope, AssignTypeMismatch, UnsupportedMutVarType)
with #[error('[code]: msg')] Display attrs matching the cli-diag-
human bracketed-code convention; code() + ctx() arms emit
kebab-case codes and structured JSON payloads.
- synth signature: new parameter mut_scope_stack: &mut Vec<IndexMap<
String, Type>> after locals, threaded through every recursive call
site (synth's 18 internal calls + mono.rs:712/1337 re-synth +
lift.rs:723 + builtins.rs test helpers + the mq.3 in-test helper
at lib.rs:6663). Stack is per-walk and lexically scoped — push on
Term::Mut entry, pop on exit. Each frame is an IndexMap so
declaration order is preserved for the diagnostic 'available' list.
- Term::Var resolution: prepended with innermost-first mut-scope
lookup. Mut-vars are monomorphic — no Forall instantiation, no
free_fn_owner recording. Innermost-wins shadowing falls out of
the iteration order.
- Term::Mut arm: gate var types to Int/Float/Bool/Unit only via
a small is_supported_mut_var_type helper; each var's init is
synth'd in the in-progress scope (the var itself is not yet
bound, so it does not self-shadow during init); push completed
frame, synth body, pop. Block's type is body's type.
- Term::Assign arm: walk mut_scope_stack innermost-first looking for
name. On miss: MutAssignOutOfScope with available flattened
across all frames (innermost-first, deduplicated, preserving
order). On hit: synth value, unify against declared type — on
mismatch emit AssignTypeMismatch with rendered types; on success
produce Type::unit().
- Five .ail.json fixtures under examples/ exercising each
diagnostic plus a positive nested-shadow sanity case, driven by
the new pin test crates/ailang-check/tests/mut_typecheck_pin.rs
(load_workspace + check_workspace + assert exact codes).
- carve_out_inventory.rs EXPECTED extended 7 → 12 to cover the new
negative-fixture set (consistent with the form-a-default-authoring
spec §C4(b) precedent for type-rejection fixtures staying as
.ail.json-only).
Plan deviations from recon: three additional synth() call sites
beyond the four enumerated (lift.rs:723, builtins.rs x2,
lib.rs:6663) surfaced via the build-red structural signal; each
threaded with a fresh empty stack. carve_out_inventory.rs extension
was required by the existing pin but not named in the recon — a
documentary concern for the next planner pass.
Tests: 579 → 592 green; examples/mut.ail typechecks clean
('ok (26 symbols across 2 modules)') via cargo run --bin ail --
check examples/mut.ail; cargo build green; full workspace test
green.
Journal: docs/journals/2026-05-15-iter-mut.2.md.
Refs: docs/specs/2026-05-15-mut-local.md, docs/plans/2026-05-15-iter-mut.2.md.
Brummel
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