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fix(runtime): an accessor call must not corrupt the caller's this (found while diagnosing #9417) - #9444
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…erryTS#9417) `invoke_accessor_getter` / `invoke_accessor_setter` saved the previous occupant of the GC-rooted `IMPLICIT_THIS` cell in a bare Rust local and restored it after running the accessor body — which is user code, so it allocates. A copying minor there relocates the caller's receiver and rewrites every slot it can see; a Rust local is not one, so the restore reinstalled a retired from-space address as the caller's `this`. Nothing faults: `js_object_get_own_field_or_undef` fails its `obj_type == GC_TYPE_OBJECT` check on the retired cell and returns TAG_UNDEFINED, so `this.<field>` silently answers `undefined` and the NEXT member access throws naming a property several steps downstream. claude-code reported it as `Cannot read properties of undefined (reading 'def')` where node says `Not logged in · Please run /login`. Roots `prev`, the receiver, the accessor closure bits and the setter's assigned value in a `RuntimeHandleScope`, re-read at each point of use — `coerce_call_this` (primitive boxing) and `clone_closure_rebind_this` (fresh ClosureHeader) both allocate too. test-files/test_gap_9417_accessor_this_restore.ts prints `caller-this bad=30` on unfixed main, deterministically and with no GC env knobs; byte-identical to node after.
📝 WalkthroughWalkthroughThe runtime now roots accessor values across allocating calls and user-code execution. A regression test forces minor garbage collection during getter calls and checks both getter and caller ChangesAccessor
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🟡 Moderate · up to The fix preserves accessor receivers across garbage collection, but an accessor that throws and is later caught may leave the caller's receiver context incorrect for subsequent operations. Merge should wait for exception-path restoration or explicit owner acceptance; the maintainer-owned release version changes should also be reverted. 🚥 Pre-merge checks | ✅ 3 | ❌ 2❌ Failed checks (2 warnings)
✅ Passed checks (3 passed)
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In `@Cargo.toml`:
- Line 338: Revert the contributor-owned release metadata changes: restore the
existing [workspace.package] version at Cargo.toml lines 338-338 and restore the
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CLAUDE.mdCargo.tomlchangelog.d/9417-accessor-implicit-this-restore.mdcrates/perry-runtime/src/object/field_get_set/accessors.rstest-files/test_gap_9417_accessor_this_restore.ts
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Leave release metadata for the maintainer.
Revert these version updates. This PR already includes changelog.d/9417-accessor-implicit-this-restore.md, which is the contributor-owned release record.
Cargo.toml#L338-L338: restore the existing[workspace.package]version.CLAUDE.md#L11-L11: restore the existingCurrent Versionvalue.
Based on learnings, contributors must not change [workspace.package] versions or the CLAUDE.md Current Version line; the maintainer updates release metadata during release.
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In `@Cargo.toml` at line 338, Revert the contributor-owned release metadata
changes: restore the existing [workspace.package] version at Cargo.toml lines
338-338 and restore the existing Current Version value at CLAUDE.md lines 11-11.
Leave the changelog record unchanged.
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Revert the 0.5.1520 bump and its Cargo.lock churn; none of the sibling campaign PRs touch version metadata.
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…ite to an unread scalar-replaced field no longer stores through null (#9460) (#9519) * fix(codegen): a rejected sloppy `o.x += 1` / `for (o.x of …)` / `[o.x] = arr` no longer throws (#9459) // sloppy (.cts, no "use strict") const o = {x:1}; Object.freeze(o); o.x += 1; // node: silent Perry: TypeError for (o.x of [7]) {} // node: silent Perry: TypeError [o.x] = [7]; // node: silent Perry: TypeError (expression position) o[k] += 1; // node: silent Perry: TypeError o.x++; // node: silent Perry: silent (correct, Expr::PropertyUpdate) o.x = 9; // node: silent Perry: silent (correct, Expr::PutValueSet) ES2024 6.2.5.7 (PutValue) performs Set(O, P, V, Throw) with Throw = IsStrictReference(ref), and 10.1.9 (OrdinarySet) reports `false` -- not a throw -- for a non-writable own or inherited data property, an accessor with no setter, and a new property on a non-extensible object. The reference's own strictness is what turns that `false` into a TypeError. The ordinary-object mirror of #9394 (arrays, fixed by #9426) and the opposite direction from #9422 (an under-throw in strict code). A CommonJS bundle is sloppy top to bottom, so this was a hard failure: a spurious TypeError stopped a program node runs to completion. Root cause: `Expr::PropertySet` carries no strictness field at all, and its codegen tail reaches `js_typed_feedback_object_set_field_by_name_fast` -> `js_object_set_field_by_name`, which has no `strict` parameter and rejects by throwing. `o.x++` was right because it lowers to `Expr::PropertyUpdate` (carries `ctx.current_strict`); `o.x = 9` was right because it lowers to `Expr::PutValueSet` (carries `strict`). Only the spellings that lower to `Expr::PropertySet` -- compound and logical assignment, for-of heads, expression-position destructuring targets -- had no answer to give. The same hole existed on `Expr::IndexSet`'s OBJECT-by-name arms, which #9426 left behind when it carried the flag to that node's array element lanes. The flag comes from the CONTEXT, exactly as #9426 did for `Expr::IndexSet`: `ctx.is_strict_fn` at the ordinary dispatch, `PutValueSet::strict` at the two sites that synthesize a `PropertySet` from a `PutValue`. Deliberately not a new HIR field: `Expr::PropertySet` has 181 mentions across the workspace (119 constructions, 54 in production code), and a large minority live in collectors and transform passes that REBUILD an existing node with no strictness context to copy -- exactly where a wrong default hides. `FnCtx::is_strict_fn` is already the audited answer for the enclosing code (`Function::is_strict`, `Expr::Closure::is_strict`, `Module::init_is_strict` from #9458, and a hard `true` for class methods). Sloppy stores route to `js_put_value_set(target, key, value, receiver, 0)` -- the receiver-aware [[Set]] sloppy `o.x = v` has always used -- so the spellings agree instead of diverging by lane. The class-field fast arm is preserved through `try_lower_sloppy_class_field_store` (#7288/#5094), whose #5093 inline precheck declines every receiver whose store could be rejected, so that arm is mode-independent and only its miss needed a sloppy tail. Strict lowering is byte-identical to before. Two IR tests moved, both because their fixture builders hard-code `is_strict: false` while their subject (the typed-feedback PropertySet site, the property-id store ABI) lives on the strict lane -- the same expectation move #9458 made when `Module::init_is_strict` landed. Each is now asserted on the strict lane AND given a sloppy twin, so neither invariant is pinned on only one of two tails. Verified byte-identical to `node --experimental-strip-types` on test-files/test_gap_9459_property_set_strictness.cts (19 lines differed on unfixed origin/main); perry-codegen --lib 1383 passed / 0 failed; targeted IR suites (typed_feedback, native_proof_regressions, scalar_replaced_slot_roots, class_field_store_pointer_test, shadow_slot_hygiene) 334 passed / 0 failed. Not changed, both pre-existing on main and documented in the fixture: `caller`/`arguments` keep their `js_object_set_field_by_name` route in both modes (that entry's poisoned-accessor handling is not a Throw-flag decision), and strict `+=` against an INHERITED rejecting receiver still skips the prototype walk -- a missing walk rather than a missing Throw flag, filed as #9495. * fix(codegen): SIGSEGV storing to a scalar-replaced object-literal field that is never read (#9460) "use strict"; const o = { x: 1 }; o.x = 7; // SIGSEGV -- nothing reads o.x const p = { x: 1 }; for (p.x of [7]) {} // SIGSEGV, sloppy or strict const q = { x: 1 }; q.y++; // TypeError "Cannot assign to read only property 'y'" Three lines of ordinary code, in both modes. The fault is `str d0, [x8]` with x8 = 0x10 -- a raw field store through a NULL receiver at null + sizeof(ObjectHeader). `stmt/let_stmt.rs`'s scalar-replacement arm elides the heap allocation for a non-escaping `new` and gives each field a stack alloca. For the synthetic `__AnonShape_*` class an object literal lowers to, it creates slots only for the fields in `non_escaping_new_used_fields` -- which tracked READS only, on the argument that a store nothing ever reads is unobservable and its slot can be elided. That is true of the STORE and false of the SLOT: the same arm registers `ctx.locals[id]` as an uninitialized DUMMY alloca (the binding has stopped being an object), so a store lowering that looks up the field slot and finds none does not stop -- it falls through to the class-field / Ptr<Shape> lanes, which load that dummy as an `ObjectHeader*`. The read side has had the matching guard since the synthetic-shape work (`expr/property_get.rs`, whose comment names this exact hazard: "the generic runtime helper that crashes on the dummy slot"). The write side never got it, and needed it on THREE lanes: `Expr::PropertySet` (`o.x += 1`, `for (o.x of ...)`), `Expr::PutValueSet` (`o.x = v`, via `try_lower_sloppy_class_field_store` and the write IC), and `Expr::PropertyUpdate` (`o.y++`). So the fix is at the source, in the two collectors that decide which fields get slots, rather than in each lane: - collectors/escape_news.rs: `non_escaping_new_used_fields` counts a WRITE as a use, so a written field always has a slot. #9024's rule one step further -- #9024 escapes a write to an UNDECLARED property because it would have no slot; this gives a slot to a DECLARED property that would otherwise have none. It costs nothing at runtime (a store into an alloca nothing loads is removed by LLVM). The walker also had NO arm at all for `Expr::PutValueSet`, which is what `o.x = v` lowers to, so neither the written field nor the value's own nested uses were being recorded. - collectors/escape_check.rs: the `Expr::PropertyUpdate` arm gains #9024's `class_chain_has_field` check that the `PropertySet` and `PutValueSet` arms already had. - expr/property_set.rs: a backstop mirroring `property_get.rs` -- a store to a scalar-replaced local with no field slot lowers the value for its side effects and discards the store, the same shape the `this` arm below it has always had. With the collector fixes this should no longer be reachable; kept because the failure it prevents is a null-pointer store and the read side carries the identical guard. Two corrections to the report, which said the crash "does not reproduce in isolation -- the preceding throws are required": - It reproduces in THREE LINES with no exception at all. The original isolated attempt printed `o.x` afterwards, and that read is what creates the slot and hides the crash. "Several rejections first" was the shape it was found in, not the condition. - It is NOT specific to sloppy mode, so it survives the #9459 fix rather than being masked by it -- confirmed by running the fixture against a build with #9459 applied and #9460 not: still SIGSEGV, at the strict case. Neither the `perry_sjlj_try` transport (#9323) nor a rooting hole (#9417/#9444/#9445) is involved: PERRY_GC_PROTECT_FROMSPACE changes nothing, because the address was never a heap object. Verified byte-identical to `node --experimental-strip-types` on test-files/test_gap_9460_unread_scalar_field_store.cts (SIGSEGV before, clean after), and the #9422/#9423 investigation's original `r_lanes.cts` repro now matches node exactly. --------- Co-authored-by: Ralph Küpper <ralph@skelpo.com>
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…t brackets (PerryTS#9445) Every `let prev = js_implicit_this_set(receiver); …user code…; js_implicit_this_set(prev)` in the runtime held the caller's receiver in a bare Rust local across a call that allocates. An evacuating young-gen minor inside the window moves that object; the restore then installed a retired from-space address as the caller's `this`, which reads as `undefined` on the next member access (the PerryTS#9417 shape). Root the saved value in a RuntimeHandleScope and re-read it at the restore — the idiom PR PerryTS#9444 used for the accessor sites — at all 121 remaining sites, plus the receivers that three of those sites consume again after the call. Claude-Session: https://claude.ai/code/session_01L11XMMWrR9Wz11dHpq4gXS
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…t brackets (#9445) Every `let prev = js_implicit_this_set(receiver); …user code…; js_implicit_this_set(prev)` in the runtime held the caller's receiver in a bare Rust local across a call that allocates. An evacuating young-gen minor inside the window moves that object; the restore then installed a retired from-space address as the caller's `this`, which reads as `undefined` on the next member access (the #9417 shape). Root the saved value in a RuntimeHandleScope and re-read it at the restore — the idiom PR #9444 used for the accessor sites — at all 121 remaining sites, plus the receivers that three of those sites consume again after the call. Claude-Session: https://claude.ai/code/session_01L11XMMWrR9Wz11dHpq4gXS
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A real, previously unknown silent-wrong-answer defect, found while diagnosing #9417. It is not #9417's cause — that diagnosis is posted on the issue and the issue stays open. Landing this on its own merit.
The defect
crates/perry-runtime/src/object/field_get_set/accessors.rs:464/493, ininvoke_accessor_getter/invoke_accessor_setter:previs a bare Rust local held across the entire accessor body. That body is user code and can allocate, so an evacuating young-gen minor can move the objectprevpoints at — and the restore then installs a retired from-space address as the caller'sthis.Nothing crashes at that point. The stale pointer is read later,
obj_type == GC_TYPE_OBJECTfails on the recycled cell, and the read answersundefined— so the failure surfaces as a property access onundefinedseveral steps downstream, naming a property that has nothing to do with the defect.The same shape applies three more times in that file:
get_bits/set_bitsacrosscoerce_call_this(primitive boxing allocates), the receiver acrossclone_closure_rebind_this(allocates a freshClosureHeader), and the setter'svalue. All four are now held in aRuntimeHandleScopeand re-read at point of use. This is longjmp-safe:exception.rssaves and restores the handle stack at trap boundaries.The correct idiom already exists in-tree —
iterator_helpers.rs:157andprototype_chain.rs:551/572root theirs. These sites were simply missed.Verification
test-files/test_gap_9417_accessor_this_restore.tson unfixedorigin/main@70eaabe57:Deterministic — no GC environment knobs required — identical across 3/3 runs, and it reproduces cc's exact error message. After the fix, byte-identical to
node --experimental-strip-types, 3/3.The file contains a second
getter-thishalf that pins the contract but never failed; the fixture says so in a comment rather than implying both halves demonstrate the gap.cargo test -p perry-runtime --lib -- --test-threads=1→ 2929 passed, 0 failed, 4 ignoredscripts/run_gap_tests.sh→ 621 tests, 616 pass, 5 fail, 0 compile-fail, 0 crash (99.1%),GAP_RC=0, "Gap snapshot OK". The 5 failures are the pre-existinggap_snapshot.jsonentries; the new test passes without a snapshot edit.What this does NOT fix
cc level: no measurable improvement. Same toolchain and flags, base vs fixed binary: 8/8 vs 8/8
reading 'def'in one batch; 6/25 vs 16/25 and 11/25 vs 9/25 in another — the rate swings with machine load and there is no effect.PERRY_GC_MOVING_LOOP_POLLS=0still makes the fixed binary correct 6/6, so cc's residual is the same GC class but a different site. See the #9417 diagnosis comment for the actual root cause (a codegen precise-root gap).I am landing this separately rather than folding it into a #9417 fix, because it is independently demonstrated, independently verified, and its own regression test would otherwise be lost inside a much larger change.
Follow-up identified
Roughly 20 more unrooted
js_implicit_this_set(prev)save/restores exist in perry-runtime with the identical latent shape —timer.rs×3,node_stream.rs×3,node_stream_readwrite.rs×4,os_process_streams.rs×3,property_key.rs×4, plusdescriptor_state.rs,dgram.rs,event_target.rs,util_promisify.rs,map.rs,set.rs,class_constructors.rs. Filed as a sweep rather than fixed here, to keep this change reviewable against its demonstrated test.Summary by CodeRabbit
Bug Fixes
thisremains correct even when garbage collection occurs during execution.Tests
thispreservation during allocation-heavy operations.Documentation
Chores