Improve TypeError diagnostics in WeakMap, WeakSet and Object builtins and update tests

[mrhapile]

Improve TypeError diagnostics in WeakMap, WeakSet and Object builtins and update tests

This Pull Request fixes/closes #.

It changes the following:

• Improve TypeError messages in WeakMap, WeakSet, and Object builtins to provide clearer diagnostics.
• Replace generic error messages such as "called with non-object value" and "Expected an object" with explicit messages indicating the expected receiver type.
• Standardize error message format to:
  <Builtin>.<method>: expected 'this' to be a <Type> object
• Update unit tests to match the improved error messages.

Before

Some errors used generic messages that did not clearly indicate which builtin method failed or what type was expected.

Examples:

WeakMap.get: called with non-object value
WeakMap.getOrInsertComputed: called with non-object value
Object prototype may only be an Object or null: undefined
Expected an object

These messages lacked clear context about the failing method or the expected this value.

After

Error messages now explicitly describe the expected receiver type and the builtin method where the error occurred.

Examples:

WeakMap.prototype.get: expected 'this' to be a WeakMap object
WeakMap.prototype.getOrInsert: expected 'this' to be a WeakMap object
WeakMap.prototype.getOrInsertComputed: expected 'this' to be a WeakMap object
Object.create: expected 'proto' to be an Object or null, got `undefined`
Object.defineProperty: expected 'this' to be an Object
Object.defineProperties: expected 'this' to be an Object

Files Modified

Engine changes

• core/engine/src/builtins/weak_map/mod.rs
• core/engine/src/builtins/weak_set/mod.rs
• core/engine/src/builtins/object/mod.rs

These files were updated to replace generic TypeError messages with more descriptive diagnostics.

Test updates

To keep the test suite consistent with the improved diagnostics, expected error strings were updated in:

• core/engine/src/builtins/weak_map/tests.rs
• core/engine/src/builtins/object/tests.rs

No behavioral changes were introduced; only error message diagnostics were improved and tests updated accordingly.

[Copilot]

Pull request overview

This PR improves TypeError diagnostics for receiver/argument validation across the WeakMap, WeakSet, and Object builtins, and updates unit tests to assert the new, more explicit error messages.

Changes:

• Update WeakMap/WeakSet prototype methods to emit clearer “expected 'this' …” TypeErrors when called with an invalid receiver.
• Improve Object builtin TypeError messages (e.g., Object.create, Object.setPrototypeOf, legacy __defineGetter__/__defineSetter__, etc.).
• Update unit tests to match the revised diagnostics.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
core/engine/src/builtins/weak_set/mod.rs	Updates WeakSet prototype receiver TypeError messages to be more explicit.
core/engine/src/builtins/weak_map/mod.rs	Updates WeakMap prototype receiver TypeError messages to be more explicit.
core/engine/src/builtins/weak_map/tests.rs	Adjusts WeakMap tests to assert the new receiver TypeError strings.
core/engine/src/builtins/object/mod.rs	Refines TypeError messages for several Object builtins (create/setPrototypeOf/defineProperty/defineProperties/legacy accessors).
core/engine/src/builtins/object/tests.rs	Updates Object.create error-message assertions to match the new wording.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.

[Copilot]

The TypeError message here refers to "'this'" being an Object, but this check is validating the first argument (args[0]) is an object. This makes the diagnostic misleading (the call receiver is ignored for this builtin). Consider updating the message to refer to the object/target parameter (and ideally include the received type) instead of 'this'.

[Copilot]

Same issue as Object.defineProperty: the error message says it expected 'this' to be an Object, but the code is rejecting non-object first arguments. Updating the message to reference the first parameter (and possibly the received type) would make the diagnostics accurate.

Suggested change

	.with_message("Object.defineProperties: expected 'this' to be an Object")
	.with_message("Object.defineProperties: expected first argument to be an object")

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	49,902	49,902	0
Ignored	2,222	2,222	0
Failed	839	839	0
Panics	0	0	0
Conformance	94.22%	94.22%	0.00%

Tested main commit: 55aed13ba6afc4c1f93b74348b225549e5ed713c
Tested PR commit: fef881c2ae389c8d5d8ad4861ed879f5a539441c
Compare commits: 55aed13...fef881c

[hansl]

Have you thought refactoring to use the js_error! macro instead?

[codecov]

Codecov Report

❌ Patch coverage is 32.69231% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.37%. Comparing base (6ddc2b4) to head (fef881c).
⚠️ Report is 829 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/builtins/object/mod.rs	12.00%	22 Missing ⚠️
core/engine/src/builtins/weak_map/mod.rs	57.89%	8 Missing ⚠️
core/engine/src/builtins/weak_set/mod.rs	37.50%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4863       +/-   ##
===========================================
+ Coverage   47.24%   58.37%   +11.12%     
===========================================
  Files         476      559       +83     
  Lines       46892    61409    +14517     
===========================================
+ Hits        22154    35846    +13692     
- Misses      24738    25563      +825     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[mrhapile]

Have you thought refactoring to use the js_error! macro instead?

I’ve refactored the error construction to use the js_error! macro instead of JsNativeError::typ().with_message(...) across the affected files. This also allowed removing the now-unused JsNativeError imports. All tests pass after the refactor. @hansl

[mrhapile]

@hansl Could you please review this? I’d like to make any necessary changes based on your feedback.

[jedel1043]

Yep, the error messages look much better!