fix(hir): preserve nested object callback methods (#9701)

[proggeramlug]

Summary

• defer callback/comparator Array fast paths when a nested property receiver is
  not proven to be an Array
• retain dense Array HIR for statically typed nested Array fields
• add lowering-verdict and executable parity regressions for the reported
  React Children.map(children, callback) shape

Root cause

The failing Lw5 frame calls qC.default.Children.map(children, callback).
The arbitrary-expression Array lowering selected ArrayLikeMethod from the
method name and two-argument shape alone. It therefore interpreted children
as the Array callback and threw object is not a function before React's own
method was entered.

Unknown nested property receivers now fall through to shape-aware dynamic
dispatch. Real Arrays still select the runtime Array implementation, while
plain objects retain their own methods. This is a deterministic dispatch bug,
not a Yoga or GC failure.

PR #9700's prerequisite promise fix has landed on main through merge train
#9711; this branch is rebased on that result.

Validation

All compilation and runtime checks below ran on perrymaster.skelpo.net:

• cargo build --release -j4 -p perry -p perry-runtime-static -p perry-stdlib-static
• cargo test --release -p perry-hir --lib (382 passed, 1 ignored)
• cargo test --release -p perry --test issue_9701_nested_object_map -- --nocapture
• pre-fix executable regression: TypeError: object is not a function
• patched Perry output matches Node: custom-map-entered, 3,6, 8,10
• compiled the full cc 2.1.112 bundle and completed onboarding from a fresh HOME
  through theme selection and REPL entry (VERDICT: PASS)
• repeated the full fresh-HOME onboarding run with
  PERRY_GC_PROTECT_FROMSPACE=1 (VERDICT: PASS)
• cargo fmt --all -- --check
• ./scripts/check_file_size.sh
• python3 scripts/check_test_registration.py
• git diff --check

No version metadata was changed.

Closes #9701.

Summary by CodeRabbit

• Bug Fixes
  • Fixed method dispatch for nested object properties with names shared by array methods, such as map, filter, and reduce.
  • Calls like React’s Children.map now correctly use the object’s own implementation instead of being treated as array operations.
  • Preserved optimized array behavior when the receiver is known to be an array.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Team

Run ID: 57c7c941-1c1a-465b-b101-488ee6d86465

📥 Commits

Reviewing files that changed from the base of the PR and between 28c2925 and ed7af75.

📒 Files selected for processing (6)

• changelog.d/9701-nested-object-array-method.md
• crates/perry-hir/src/lower/expr_call/array_only_methods.rs
• crates/perry-hir/src/lower/expr_call/array_only_methods_tests.rs
• crates/perry-hir/src/lower/expr_call/mod.rs
• crates/perry/tests/issue_9701_nested_object_map.rs
• test-files/test_issue_9701_nested_object_map.ts

Included review availability: Your plan provides up to 8 included reviews per hour; 7 remain after this review.

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📝 Walkthrough

Walkthrough

Nested callback-taking array methods now defer lowering for ambiguous nested property receivers. New unit and integration tests verify custom nested method dispatch and retain optimized lowering for statically typed arrays.

Changes

Nested array-method dispatch

Layer / File(s)	Summary
Ambiguous receiver lowering crates/perry-hir/src/lower/expr_call/array_only_methods.rs, crates/perry-hir/src/lower/expr_call/mod.rs, crates/perry-hir/src/lower/expr_call/array_only_methods_tests.rs	Nested callback and comparator-taking methods use dynamic dispatch unless the receiver is proven to be an array. Unit tests cover custom nested methods and typed array specialization.
Nested method regression coverage test-files/test_issue_9701_nested_object_map.ts, crates/perry/tests/issue_9701_nested_object_map.rs, changelog.d/9701-nested-object-array-method.md	The integration fixture exercises nested Children.map and an array stored behind an untyped property. The test validates the compiled output, and the changelog records the fix.

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

Merge Risk: ⚪ Minimal · up to ed7af

This change preserves custom nested method dispatch while retaining optimized handling for proven arrays, with targeted lowering and runtime regression coverage. No merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 9 functions across 5 files. (1 skipped: 1…	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 changes address issue [#9701] by preventing nested object methods such as React Children.map from being incorrectly lowered as Array methods. The implementation preserves Array specialization when…
Out of Scope Changes check	✅ Passed	The implementation, changelog entry, unit tests, integration test, and TypeScript fixture all support the nested object method dispatch fix described in [#9701]. No unrelated code changes are evident.
Title check	✅ Passed	The title clearly and concisely identifies the HIR fix for nested object callback methods, which is the main change.
Description check	✅ Passed	The description provides a clear summary, root cause, implementation details, related issue, validation commands, regression coverage, and output results. It does not use every template heading or che…

Full details: Docstring Coverage

Explanation

Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 9 functions across 5 files. (1 skipped: 1 unsupported.)

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[proggeramlug]

Landed on main via merge train #9723 (rebase-merged, so your commit keeps its authorship). Thanks!