[dextermos-dev]

Summary

Closes #1358.

This pull request resolves a channel direction tracking defect in hy-check where calling a multi-return function stored in a struct field (_, rx := h.f() where f has type fn() int <-chan int) dropped channel direction constraints, allowing illegal operations like close(rx) on a receive-only channel (<-chan T) to bypass hyb check and fail during go build with cannot close receive-only channel rx.

Root Cause & Changes

1. Checker::dir_multi_ty_of_call (sendability.rs):

   • In Expr::Field { base, name, .. }, previously only checked self.method_decls and returned early if no method was found.
   • Added fallback to self.struct_fields_for_type(&base_ty). When the field resolves to TypeExpr::Fn { results, .. }, its results vector is returned so channel directions (<-chan T, chan<- T) are tracked in ChanDirEnv.

2. Checker::call_result_tys (shape.rs):

   • In Expr::Field { base, name, .. }, falls back to self.struct_fields_for_type(&base_ty) to resolve results of fn-typed struct fields.
   • In the wildcard other arm, falls back to self.ty_of_expr(st, other) to resolve result types of direct fn-typed expressions.

Verification

• Added dedicated test suite in compiler/crates/hy-check/tests/chan_dir_fn_struct_field_1358.rs:
  • rejects_closing_recv_only_channel_from_struct_field_fn_call_issue_1358 (verifies HYB-E3009)
  • rejects_sending_to_recv_only_channel_from_struct_field_fn_call_issue_1358 (verifies HYB-E3008)
  • rejects_receiving_from_send_only_channel_from_struct_field_fn_call_issue_1358 (verifies HYB-E3008)
  • accepts_valid_channel_directions_from_struct_field_fn_call_issue_1358 (verifies valid send/recv/close operations pass)
• Verified all 4 tests pass (4 passed, 0 failed).
• Verified cargo test -p hy-check sendability passes.
• Verified tools/check_conflict_markers.py and tools/check_corpus_census.py pass clean (127/127 programs).

Settlement Wallet: 0x8366bCe3a2D379Dec7656D7A67015789FaF999f20