fix(runtime): resolve an ancestor's #private brand through the instance's evaluation heritage chain

[proggeramlug]

Fixes #11127
Fixes #11131

Root cause (shared)

Both issues have one runtime cause.

A class declared inside a function is lowered as a per-evaluation class (ClassExprFresh). So is a top-level class that captures a CommonJS-wrapper local. In #11131, const EventEmitter = require("events") puts the module body in the CJS wrapper, and Client captures EventEmitter. That capture is the only part EventEmitter plays: it explains why the import { EventEmitter } form works, and why a user class that is not captured works.

new E() stamps the instance with E's evaluation (meta.private_evaluation_brand). When an inherited method S.read() is dispatched, S's evaluation is pushed as the lexical private brand. private_evaluation_brand(instance, S) then compared the stamp to S's template id exactly. It got None, so every this.#x in a base method threw Cannot access private member from an object whose class did not declare it on a subclass instance. Getters did not throw because they take a path that falls back to the per-field marker, which is why a.l worked but a.read() did not.

I confirmed this with runtime instrumentation. In the method frame, the lexical brand was S's evaluation, the instance stamp was E's evaluation, and the marker was present.

Fix (perry-runtime, 3 files)

For an instance, private_evaluation_brand now walks from the stamped evaluation up each fresh class object's pinned per-evaluation parent (__perry_parent_class, written by js_class_object_pin_parent). It returns the ancestor evaluation for the declaring template. The walk reuses pinned_class_object_for_ancestor from class_constructors.rs, which constructor replay already uses (visibility raised to pub(crate)).

• The walk stops at the first heritage that is not a class object (a static ClassRef, a closure or a builtin) and returns None, the same result as before.
• A class-object receiver (static private members) keeps the exact comparison. Static private elements are not inherited.
• The guard still requires the per-field marker afterwards, so the walk cannot admit an uninitialized element.
• The brand stays exact per evaluation. The gap test checks that a second evaluation's read rejects the first evaluation's instance with a TypeError, and that #l in gives false across evaluations.

Scope and sibling PRs

• Base: current origin/main (36892b7), rebased. Main's 86cb666 makes dynamic-heritage class expressions without static methods evaluate per call, so @redis/client's attachConfig shape (class extends BaseClass {} built in a helper whose extends operand is a parameter) now gets its own evaluation stamp. The walk covers it without fix(hir): give each evaluation of a dynamic-heritage class expression its own class (#11042) #11122 (closed). The 11131 gap test now includes that shape. It fails on main and passes on this branch.
• Still open, filed as Subclass built inside a per-evaluation class's own static method fails '#x in' and instanceof against that class (redis RedisClient.factory shape) #11142: a subclass built inside the base class's own static method (redis's RedisClient.factory). The inherited this.#x read works, but #x in and instanceof return false. The likely cause is that the in-body self-reference RC lowers to the template ClassRef, so the pinned parent chain never reaches the evaluation. That is outside this PR.
• Compatible with fix(codegen): stage no ancestor field initializers a delegated constructor installs itself (#11120) #11129: it merges with no conflicts.

Tests

• test-files/test_gap_11127_private_field_function_local_subclass.ts: method, getter, ++, +=, #l in, a private method, a grandchild, a direct base instance, cross-evaluation rejection, and a factory class expression extending a function-local base.
• test-files/test_gap_11131_private_field_cjs_require_subclass.ts: the issue's shape plus a RedisSocket/RedisClient mirror. Node runs test-files/*.ts as ESM (the repo package.json has "type": "module"), where a bare require is undefined. So this test spells the CJS wrapper scope out as a module-body function with the required EventEmitter as a local.
• crates/perry/tests/private_brand_ancestor_evaluation.rs (new suite): the literal bare-require repro as a .cjs entry and as a .ts entry, with Node 26.5.1's output hardcoded.
• perry-runtime unit test instance_ancestor_evaluation_brand_tests: F→E→S pinned chain. I sabotage-checked it: with the walk disabled it fails at the E assertion (left: None).

Validation (first run on 784ed8e; after the rebase, both gap tests, both integration tests and the private-related runtime unit tests were re-run on 36892b7 with the same verdicts)

(perrymaster, perry-dev builds, Node 26.5.1 at /opt/node-v26.5.1-linux-x64)

• Fails on main, passes with the fix: both issue repros, both new gap tests, and both .cjs and .ts integration fixtures. Main prints private threw Cannot access private member… for Private field holding new EventEmitter() from require("events") is unreadable when its class is constructed as a parent (next redis createClient blocker) #11131, and 0 followed by that TypeError for Base-class method can't read its #private field on a subclass instance when both classes are function-local #11127. The fix arm matches Node byte for byte.
• Related gap A/B, compile-and-diff against Node 26.5.1 (78 tests matching private/brand/extends/class-expr/subclass/events/heritage/super, plus every gap test using this.# or #x in), with main and the fix built the same way: main 73/78, fix 75/78. The only changes are the two new tests going FAIL→PASS. The 3 remaining failures are identical on both arms (enum_in_function_body, events_import_4995, gc_http2_pending_event_callback_rooting; raw byte compare, no harness normalization).
• cargo test -p perry-runtime --lib (RUST_TEST_THREADS=1, perry-dev): 4368 passed, 0 failed, 5 ignored.
• cargo test -p perry --test private_brand_ancestor_evaluation: 2 passed.
• cargo fmt --all -- --check: OK. scripts/check_file_size.sh: OK.
• SKIP_COMPILE_GATES=1 scripts/run_lint_gates.sh: 87 of 88 script gates passed. The one failure is cargo xwin check, because cargo-xwin is not installed on the host (no such command: xwin), not because of this change. The compile tier was not run.

redis@6.1.0 end-to-end

I tested createClient({ socket }) against a private redis-server on port 26531, using this branch with #11122 and #11129 merged on top and an auto-optimize build. It gets past the #11131 error in client.connect(). It then reports Redis Client Error TypeError: Cannot read properties of undefined (reading 'reject') and hangs until the timeout. That read is in commands-queue.js's #onErrorReply: this.#waitingForReply.shift().reject(err). #waitingForReply is new linked_list_1.EmptyAwareSinglyLinkedList(), and entries go in through .push(toSend). That matches #11128 (a user push method on an instance from new <any class value> loses its effects), so #11128 is the likely next blocker. I have not confirmed this with instrumentation.

Not run

• The gap harness (run_parity_tests.sh) itself. Port 17891 was held by another agent's sweep the whole time, so I used the compile-and-diff loop above.
• A full gap sweep, instruction-count perf stat A/B, a -D warnings workspace check on the default dev profile, and cargo test for crates other than perry-runtime and the new perry suite.
• No existing test in another suite is expected to change. None of the A/B tests changed apart from the two new ones.

Summary by CodeRabbit

• Bug Fixes

  • Fixed inherited private-field access on instances of per-evaluation subclasses. Parent methods can now read and write private fields, and private-brand checks work across class inheritance.
  • Preserved separate private names across class evaluations, so private access from one evaluation does not apply to instances from another.

• Tests

  • Added coverage for function-local subclasses, dynamically created subclasses, and CommonJS require scenarios, including inherited field access and private-brand checks.

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📝 Walkthrough

Walkthrough

The runtime now resolves instance private brands through pinned per-evaluation class ancestors. New unit and integration tests cover inherited private access, class-evaluation boundaries, and CommonJS and TypeScript entry points.

Changes

Private brand lookup

Layer / File(s)	Summary
Resolve private brands through instance ancestry crates/perry-runtime/src/object/class_constructors.rs, crates/perry-runtime/src/object/field_get_set/ic_miss.rs, crates/perry-runtime/src/object/field_get_set/ic_miss/private_member_access.rs, changelog.d/11141-private-brand-ancestor-evaluation.md	The runtime uses pinned class-object ancestry to resolve an instance’s private brand for a declaring class. Class-object receivers retain direct class-ID matching. A unit test checks ancestor and unrelated-class lookups.
Cover inherited private access crates/perry/tests/private_brand_ancestor_evaluation.rs, test-files/test_gap_11127_private_field_function_local_subclass.ts, test-files/test_gap_11131_private_field_cjs_require_subclass.ts	New tests check inherited private-field and private-method access, private-brand checks, and behavior across class evaluations. The integration test runs a CommonJS fixture as both CJS and TypeScript entries.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant BrandLookup as private_evaluation_brand
  participant AncestorLookup as instance_ancestor_evaluation_brand
  participant PinnedParents as pinned_class_object_for_ancestor
  BrandLookup->>AncestorLookup: Resolve instance brand for declaring class
  AncestorLookup->>PinnedParents: Walk pinned class-object parents
  PinnedParents-->>AncestorLookup: Return matching ancestor evaluation or None
  AncestorLookup-->>BrandLookup: Return resolved evaluation brand

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Merge Risk: 🟡 Moderate · up to 14239

Inherited private-member access may select the wrong class evaluation in the reported case. Resolve or explicitly accept that risk before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 56.25% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 16 functions across 6 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR meets the coding requirements for #11127 and #11131. private_evaluation_brand now resolves instance brands through the stamped evaluation's pinned ancestor chain. Static private-member checks…
Out of Scope Changes check	✅ Passed	The changed runtime code, focused unit test, integration test, issue-specific tests, and changelog entry support #11127 or #11131. No unrelated product behavior is shown. The reported Redis end-to-end…
Title check	✅ Passed	The title clearly and concisely describes the main runtime change: resolving an ancestor's private brand through the instance's evaluation heritage chain.
Description check	✅ Passed	The description provides detailed root cause, implementation changes, related issues, tests, validation results, and known limitations. It does not use the template headings or complete the checklist,…

Full details: Docstring Coverage

Explanation

Docstring coverage is 56.25% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 16 functions across 6 files. (1 skipped: 1 unsupported.)

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Inline comments:
In
`@crates/perry-runtime/src/object/field_get_set/ic_miss/private_member_access.rs`:
- Around line 288-289: Update the `pinned_class_object_for_ancestor` lookup so
it matches the expected lexical evaluation against the pinned ancestry, rather
than returning the first ancestor with the same `declaring_class_id`; preserve
private-name identity across repeated evaluations of one class declaration. Add
a regression covering two evaluations of the same declaration in one inheritance
chain.

In `@test-files/test_gap_11127_private_field_function_local_subclass.ts`:
- Around line 55-57: Replace the dynamic-heritage class expression returned by
the factory with a function-local class declaration extending Counter, then
return that declared class; keep the twice method behavior unchanged so the test
exercises private-field lookup from the subclass.

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• crates/perry-runtime/src/object/class_constructors.rs
• crates/perry-runtime/src/object/field_get_set/ic_miss.rs
• crates/perry-runtime/src/object/field_get_set/ic_miss/private_member_access.rs
• crates/perry/tests/private_brand_ancestor_evaluation.rs
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[proggeramlug]

Ready for a train. Rebased onto 36892b7, head 1423921. Fixes #11131 and #11127. It now covers redis's attachConfig shape on main without #11122, which is closed. The rebase applied cleanly, but the 78-test A/B and the full perry-runtime suite ran on the previous base and were not re-run. Remaining related redis gaps have their own agents: #11142 (subclass built in the base's own static method: #x in / instanceof) and #11150 (this.#tail.next = this.#tail = node evaluation order).