test(runtime): verify apply_active_realm_protos with all-None clears overrides

[dowdiness]

Summary

Follow-up to #369. Adds a test covering the clearing path of apply_active_realm_protos — identified as a gap during review.

The test:

1. Sets an active map_proto override → verifies fast path is blocked and getter returns the override
2. Calls apply_active_realm_protos(rs, FunctionRealmProtos()) (all-None) → verifies fast path is re-allowed and getter falls back to the base proto

This exercises the branch in apply_active_realm_protos where any_set is false → writes None to active_overrides.

Test plan

• moon test interpreter/runtime: 92/92 pass
• moon check --deny-warn clean

🤖 Generated with Claude Code

Summary by CodeRabbit

• Tests
  • Added test coverage for prototype override clearing behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 78613aae-60cd-4d66-a48e-6abc65d2b1b3

📥 Commits

Reviewing files that changed from the base of the PR and between 3717dea and 6f9f0d9.

📒 Files selected for processing (1)

• interpreter/runtime/factories_wbtest.mbt

---

📝 Walkthrough

Walkthrough

A new whitebox test is added to interpreter/runtime/factories_wbtest.mbt. The test stamps a function, applies an active map prototype override, verifies fast-path blocking and get_map_proto behavior under the override, then calls apply_active_realm_protos with an all-None FunctionRealmProtos() and asserts fast-path re-enablement and fallback to the base map prototype.

Changes

Override Clearance Whitebox Test

Layer / File(s)	Summary
Whitebox test: all-None proto clears map override and restores fast path interpreter/runtime/factories_wbtest.mbt	Adds test apply_active_realm_protos with all-None clears an existing override that stamps a function, activates a map prototype override, asserts fast-path is blocked and get_map_proto returns the override, then calls apply_active_realm_protos with an all-None FunctionRealmProtos() and asserts fast-path is re-enabled and get_map_proto falls back to the base prototype.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• dowdiness/js_engine#369: Directly related — implements the realm_state.has_active_override and fast-path logic inside apply_active_realm_protos that this new test exercises when overrides are cleared.

Poem

🐇 Hop, hop, the override falls away,
The fast path blooms again today!
A None for map, a None for all—
The base prototype answers the call.
With every test, the engine's right,
This rabbit approves with pure delight! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adding a test for apply_active_realm_protos that verifies all-None values clear existing overrides.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch test/apply-active-realm-protos-clearing

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[github-actions]

Benchmark Results

Run: https://github.com/dowdiness/js_engine/actions/runs/27630432811

startup/tiny_program is the PR #153 / issue #141 guardrail for built-in realm-stamping startup cost.

Stage summary

stage	benchmarks	total mean	slowest benchmark	slowest mean	noisy rows
startup	3	2.433 ms	startup/tiny_program	1.271 ms	0
frontend	7	0.866 ms	pipeline/parse_heavy	0.493 ms	2
execution	25	14836.420 ms	exec/fibonacci_30	13439.809 ms	3

Focused bytecode base-vs-head comparison

Base-vs-head deltas are reporting-only. Negative delta and PR/base < 1.00x mean the PR is faster; interpret high-CV or noisy rows cautiously.

benchmark	stage	base mean	PR mean	delta	PR/base	base CV	PR CV	noisy
baseline/bytecode/closure_factory	execution	13.755 ms	14.305 ms	+4.0%	1.04x	6.9%	6.2%	no
pipeline/bytecode/evaluate	execution	9.086 ms	8.812 ms	-3.0%	0.97x	1.5%	1.9%	no
isolate/bytecode/call_frame	execution	8.199 ms	8.868 ms	+8.2%	1.08x	1.1%	1.0%	no
isolate/bytecode/runtime_helpers	execution	12.104 ms	12.621 ms	+4.3%	1.04x	2.2%	0.7%	no
isolate/bytecode/local_access	execution	37.532 ms	38.355 ms	+2.2%	1.02x	1.8%	1.3%	no
isolate/bytecode/env_access	execution	37.954 ms	38.772 ms	+2.2%	1.02x	3.1%	1.9%	no
isolate/bytecode/captured_access	execution	36.061 ms	35.887 ms	-0.5%	1.00x	2.4%	1.9%	no
isolate/bytecode/dispatch_stack	execution	24.300 ms	22.656 ms	-6.8%	0.93x	1.4%	0.5%	no

Base-vs-head comparison

benchmark	stage	base mean	PR mean	delta	PR/base	base CV	PR CV	noisy
startup/tiny_program	startup	1.143 ms	1.271 ms	+11.2%	1.11x	5.1%	5.8%	no
lexer/small	frontend	0.030 ms	0.030 ms	-1.0%	0.99x	26.4%	27.9%	base, PR
lexer/large	frontend	0.261 ms	0.264 ms	+1.1%	1.01x	0.8%	1.0%	no
exec/fibonacci_30	execution	13083.630 ms	13439.809 ms	+2.7%	1.03x	1.3%	0.5%	no
exec/property_chain	execution	14.869 ms	14.840 ms	-0.2%	1.00x	13.3%	8.9%	no
startup/phase/parse_tiny	frontend	0.002 ms	0.002 ms	+1.4%	1.01x	0.9%	1.7%	no
startup/phase/new_interpreter	startup	1.120 ms	1.161 ms	+3.7%	1.04x	13.2%	9.0%	no
startup/phase/execute_preparsed_tiny	execution	0.001 ms	0.000 ms	-4.4%	0.96x	0.7%	0.8%	no
startup/phase/event_loop_drain_empty	startup	0.000 ms	0.000 ms	+1.8%	1.02x	0.9%	1.3%	no
startup/phase/result_stringify_output	execution	0.000 ms	0.000 ms	-0.1%	1.00x	0.5%	0.6%	no
exec/array_map_filter	execution	21.025 ms	20.223 ms	-3.8%	0.96x	18.7%	20.8%	base, PR
exec/closure_factory	execution	29.343 ms	28.785 ms	-1.9%	0.98x	6.3%	8.5%	no
baseline/closure_legacy/closure_factory	execution	28.537 ms	28.020 ms	-1.8%	0.98x	8.0%	9.8%	no
baseline/bytecode/closure_factory	execution	13.755 ms	14.305 ms	+4.0%	1.04x	6.9%	6.2%	no
isolate/bytecode/dispatch_stack	execution	24.300 ms	22.656 ms	-6.8%	0.93x	1.4%	0.5%	no
isolate/bytecode/local_access	execution	37.532 ms	38.355 ms	+2.2%	1.02x	1.8%	1.3%	no
isolate/bytecode/env_access	execution	37.954 ms	38.772 ms	+2.2%	1.02x	3.1%	1.9%	no
isolate/bytecode/captured_access	execution	36.061 ms	35.887 ms	-0.5%	1.00x	2.4%	1.9%	no
isolate/bytecode/call_frame	execution	8.199 ms	8.868 ms	+8.2%	1.08x	1.1%	1.0%	no
isolate/bytecode/runtime_helpers	execution	12.104 ms	12.621 ms	+4.3%	1.04x	2.2%	0.7%	no
isolate/bytecode/property_get	execution	45.093 ms	45.157 ms	+0.1%	1.00x	1.8%	2.9%	no
isolate/bytecode/property_set	execution	41.783 ms	40.597 ms	-2.8%	0.97x	0.6%	2.7%	no
isolate/bytecode/method_call	execution	9.382 ms	9.979 ms	+6.4%	1.06x	0.6%	0.9%	no
isolate/bytecode/object_literal	execution	13.497 ms	13.600 ms	+0.8%	1.01x	2.6%	1.4%	no
isolate/bytecode/array_literal	execution	14.982 ms	15.005 ms	+0.2%	1.00x	1.5%	1.2%	no
exec/arithmetic_loop	execution	948.943 ms	934.861 ms	-1.5%	0.99x	0.4%	0.5%	no
exec/object_construction	execution	7.619 ms	7.610 ms	-0.1%	1.00x	11.1%	6.1%	no
exec/string_ops	execution	1.833 ms	1.987 ms	+8.4%	1.08x	12.2%	18.6%	PR
pipeline/exec/lex	frontend	0.028 ms	0.028 ms	+0.3%	1.00x	0.5%	0.8%	no
pipeline/exec/parse	frontend	0.027 ms	0.028 ms	+1.9%	1.02x	2.8%	3.3%	no
pipeline/exec/evaluate	execution	25.785 ms	30.211 ms	+17.2%	1.17x	5.0%	20.1%	PR
pipeline/closure_legacy/evaluate	execution	24.619 ms	25.462 ms	+3.4%	1.03x	4.2%	6.8%	no
pipeline/bytecode/compile	frontend	0.023 ms	0.023 ms	-0.7%	0.99x	32.1%	26.5%	base, PR
pipeline/bytecode/evaluate	execution	9.086 ms	8.812 ms	-3.0%	0.97x	1.5%	1.9%	no
pipeline/parse_heavy	frontend	0.487 ms	0.493 ms	+1.2%	1.01x	7.2%	5.0%	no

Mean-time chart (log scale)

benchmark	stage	mean	chart
startup/tiny_program	startup	1.271 ms	##
lexer/small	frontend	0.030 ms ⚠	#
lexer/large	frontend	0.264 ms	#
exec/fibonacci_30	execution	13439.809 ms	##############################
exec/property_chain	execution	14.840 ms	########
startup/phase/parse_tiny	frontend	0.002 ms	#
startup/phase/new_interpreter	startup	1.161 ms	##
startup/phase/execute_preparsed_tiny	execution	0.000 ms	#
startup/phase/event_loop_drain_empty	startup	0.000 ms	#
startup/phase/result_stringify_output	execution	0.000 ms	#
exec/array_map_filter	execution	20.223 ms ⚠	#########
exec/closure_factory	execution	28.785 ms	##########
baseline/closure_legacy/closure_factory	execution	28.020 ms	##########
baseline/bytecode/closure_factory	execution	14.305 ms	########
isolate/bytecode/dispatch_stack	execution	22.656 ms	#########
isolate/bytecode/local_access	execution	38.355 ms	###########
isolate/bytecode/env_access	execution	38.772 ms	###########
isolate/bytecode/captured_access	execution	35.887 ms	###########
isolate/bytecode/call_frame	execution	8.868 ms	#######
isolate/bytecode/runtime_helpers	execution	12.621 ms	########
isolate/bytecode/property_get	execution	45.157 ms	############
isolate/bytecode/property_set	execution	40.597 ms	###########
isolate/bytecode/method_call	execution	9.979 ms	#######
isolate/bytecode/object_literal	execution	13.600 ms	########
isolate/bytecode/array_literal	execution	15.005 ms	########
exec/arithmetic_loop	execution	934.861 ms	#####################
exec/object_construction	execution	7.610 ms	######
exec/string_ops	execution	1.987 ms ⚠	###
pipeline/exec/lex	frontend	0.028 ms	#
pipeline/exec/parse	frontend	0.028 ms	#
pipeline/exec/evaluate	execution	30.211 ms ⚠	##########
pipeline/closure_legacy/evaluate	execution	25.462 ms	##########
pipeline/bytecode/compile	frontend	0.023 ms ⚠	#
pipeline/bytecode/evaluate	execution	8.812 ms	#######
pipeline/parse_heavy	frontend	0.493 ms	#

Closure-conversion comparison

• unavailable