refactor: extract type-check boilerplate into a single require_internal_slot! macro

[Nakshatra480]

Summary

This PR introduces a new require_internal_slot! macro to replace the repetitive 5-line this-type-checking boilerplate found across the engine's built-in prototype methods.

Previously, almost every prototype method (across Temporal, Date, TypedArrays, etc.) manually downcasted this and returned a TypeError if the internal slot was missing:

let object = this.as_object();
let date = object
    .as_ref()
    .and_then(JsObject::downcast_ref::<Self>)
    .ok_or_else(|| JsNativeError::typ().with_message("'this' is not a Date"))?;

This PR refactors those occurrences into a single, much cleaner macro call that correctly handles the necessary borrowing and lifetime scoping:

require_internal_slot!(date = this, Date, "Date");

Scope of changes

While originally intended for just the Temporal built-ins, I realized this boilerplate is heavily duplicated across the entire engine. Therefore, I've broadened the scope and applied the macro to all affected built-ins, including:

• Temporal (all modules)
• Date
• ArrayBuffer & SharedArrayBuffer
• DataView
• TypedArray
• WeakRef, WeakMap, WeakSet
• Intl (Collator, Segmenter, Segments)

Error Messages & Testing

As part of standardizing this pattern, all error messages across the engine for missing internal slots have been unified to use the generic format: TypeError: "the this object must be a {Type} object.".

All existing tests (specifically in Builtin::Date) that previously relied on custom error strings like "'this' is not a Date" have been updated to expect the new standardized message. CI tests now pass cleanly with these updates.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,732	50,732	0
Ignored	1,426	1,426	0
Failed	805	805	0
Panics	0	0	0
Conformance	95.79%	95.79%	0.00%

Tested main commit: 2437b6704c4315f6ec8f0766bf229fba23e0e61e
Tested PR commit: f0b154ada75b5fbb1804b3bba535e99ebaed4bb4
Compare commits: 2437b67...f0b154a

[codecov]

Codecov Report

❌ Patch coverage is 22.13855% with 517 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.25%. Comparing base (6ddc2b4) to head (f0b154a).
⚠️ Report is 919 commits behind head on main.

Files with missing lines	Patch %	Lines
.../engine/src/builtins/temporal/zoneddatetime/mod.rs	0.00%	116 Missing ⚠️
...ngine/src/builtins/temporal/plain_date_time/mod.rs	2.00%	98 Missing ⚠️
...gine/src/builtins/temporal/plain_year_month/mod.rs	0.00%	57 Missing ⚠️
core/engine/src/builtins/temporal/duration/mod.rs	14.54%	47 Missing ⚠️
...ore/engine/src/builtins/temporal/plain_date/mod.rs	0.00%	46 Missing ⚠️
core/engine/src/builtins/temporal/instant/mod.rs	0.00%	45 Missing ⚠️
...ore/engine/src/builtins/temporal/plain_time/mod.rs	10.00%	36 Missing ⚠️
...ngine/src/builtins/temporal/plain_month_day/mod.rs	0.00%	29 Missing ⚠️
core/engine/src/builtins/intl/collator/mod.rs	0.00%	12 Missing ⚠️
...ore/engine/src/builtins/intl/segmenter/segments.rs	0.00%	10 Missing ⚠️
... and 5 more

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5233       +/-   ##
===========================================
+ Coverage   47.24%   60.25%   +13.01%     
===========================================
  Files         476      589      +113     
  Lines       46892    62702    +15810     
===========================================
+ Hits        22154    37783    +15629     
- Misses      24738    24919      +181     

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[nekevss]

I do sort of like the change for how succinct it is, and it's potential for making the code more readable.

One question: why change just the temporal objects and not the built-ins in general? Had you looked at other built-ins?

[Nakshatra480]

Hey @nekevss Thanks for the review!

To answer your question: Yes, while originally working on Temporal, I realized that the 5-line this-type-check boilerplate is heavily duplicated across almost all built-ins. I have now expanded the scope of this PR to apply the macro across the entire engine, not just Temporal.

Here is a summary of the updates in the latest push:

1. Scope Expanded: Applied the macro to all affected built-ins, including Date, ArrayBuffer, SharedArrayBuffer, DataView, TypedArray, WeakRef, WeakMap, WeakSet, and Intl (Collator, Segmenter, Segments), replacing hundreds of lines of repetitive downcasting boilerplate.
2. Macro Renamed: Renamed the macro to require_internal_slot! as suggested.
3. js_error! Used: Updated the macro to use js_error! internally as requested.
4. Error Messages: The macro standardizes the error message to TypeError: "the this object must be a {Type} object.". A few tests (specifically in Builtin::Date) that explicitly asserted the old "'this' is not a Date" error string have been updated to expect the new standardized message.

All CI tests, including cargo fmt and cargo clippy, now pass cleanly. Let me know if there's anything else you'd like me to adjust!

[Nakshatra480]

Hey @jedel1043 I've pushed the requested changes using JsObject::downcast, and all builds and tests are now passing cleanly. The PR is ready for another look whenever you have time!