Merge train: #9566 #9567 #9568 - #9572
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`const Mixed2 = mixin(Mixed)` — a mixin applied to a previous mixin's
RESULT — SIGSEGVed as soon as anything derived from it was constructed.
Node prints `4` for the issue's reproducer; Perry exited 139 after
unbounded recursion.
The HIR mixin fast path in `lower/stmt.rs` synthesizes a real class for
`const M = mixinFn(Base)`. At the second level the base is `Mixed`, a
lexical VALUE binding, so `lower_class_from_ast` takes its
locally-shadowed arm and captures the parent as `extends_expr` — a
dynamic parent — rather than a static class link. That is correct. What
was missing is the other half: unlike the sibling `const X = class {…}`
path immediately above it, this arm bound the synthesized class without
emitting the declaration-time `RegisterClassParentDynamic`. The
generated `Mixed2_constructor` therefore called
`js_get_dynamic_parent_value` for its class id with no registration to
answer it; with an undefined parent `js_fetch_or_value_super` fell back
to the most-derived receiver, re-selected `Mixed2`, and recursed until
the stack overflowed.
Emit the registration here too, in source order after the parent's own
value binding and before this class's — exactly where the sibling path
puts it. A single-level `mixin(Root)` extends a real class, keeps
`extends_expr` at `None`, and is unchanged: that is why one level
already worked (#9073) and two did not.
Verified on Linux (perrymaster) with a fresh
`PERRY_NO_AUTO_OPTIMIZE=1 cargo build --profile perry-dev -p perry
-p perry-runtime-static -p perry-stdlib-static`:
- Baseline binary built from this tree before the patch: exit 139.
- After: the gap fixture is byte-identical to the pinned Node 26.5.1
oracle under both `PERRY_NO_AUTO_OPTIMIZE=1` and the default
auto-optimize pipeline.
- LLVM for the fixture: every `js_get_dynamic_parent_value(i32 N)` in
the module now has a matching `js_register_class_parent_dynamic(i32
N, …)` — zero orphans; `Mixed2_constructor`'s id is among them.
- `cargo test -p perry-hir`: all green. The new lowering unit test was
confirmed to FAIL against the unpatched lowering.
The gap fixture keeps the issue's reproducer verbatim and adds the
assertions it left open: inherited `Root` state and the mixin method
through both synthesized levels, `instanceof` across the whole chain, a
leaf with no own constructor, the still-working one-level case, and a
three-level chain built from three distinct mixins so a dropped level
shows up as a missing method rather than being masked by identical
bodies.
Closes #9079
Claude-Session: https://claude.ai/code/session_01SNcEDcviLvFMta5oL7Zxig
This was referenced Sep 2, 2026
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Lands the validated train: #9566 (Linux callback-deopt GC coverage restored — the fixture now builds a release panic=abort runtime per the #8479 exception-transport contract, replacing the Linux ignore from #9488), #9567 (dynamic parent of a mixin-of-a-mixin registered, #9079), #9568 (child-process null-byte validation, #9537).
Validation: release build green; RUST_TEST_THREADS=1 perry-runtime green; perry-hir green; the restored deopt test passes (both evacuation arms, 175s); both gap fixtures byte-identical to node; lint gates green.
Rebase-merge preserving authorship.