fix(built-ins): permit preventExtensions on fixed-length typed arrays backed by GSABs

[AlvinThorn008]

This Pull Request fixes/closes #5256.

As required by ecma262, Object.preventExtensions may be applied to typed arrays without error if the IsTypedArrayFixedLength is not false. Prior to this commit, this check was incorrectly implemented via ArrayBuffer::is_fixed_len which does not/can not include an AUTO length check. This discrepancy lies in that the requirements of a fixed-length TypedArray slightly differ from a fixed-length arraybuffer.

It adds and replaces the checks as specified by sec-istypedarrayfixedlength. Now, typed_array_exotic_prevent_extensions should

• return Ok(false) when the TypedArray is auto length or when the backing ArrayBuffer is resizable.
• failing the above, call ordinary_prevent_extensions if the backing array is a SharedArrayBuffer.

This PR also adds a test to ensure what the title of this issue says. In addition, test262's test/staging/built-ins/preventExtensions should now pass completely.

[zhuzhu81998]

I think it would be much nicer if you implement the IsTypedArrayFixedLength operation as a function, similar to:

boa/core/engine/src/builtins/typed_array/builtin.rs

Lines 3269 to 3293 in 2437b67

	/// Abstract operation `IsValidIntegerIndex ( O, index )`.
	///
	/// Returns `true` if the index is valid, or `false` otherwise.
	///
	/// More information:
	/// - [ECMAScript reference][spec]
	///
	/// [spec]: https://tc39.es/ecma262/#sec-isvalidintegerindex
	pub(crate) fn is_valid_integer_index(obj: &JsObject, index: f64) -> JsResult<bool> {
	let inner = obj.downcast_ref::<TypedArray>().js_expect(
	"integer indexed exotic method should only be callable from TypedArray objects",
	)?;
	let buf = inner.viewed_array_buffer();
	let buf = buf.as_buffer();
	// 1. If IsDetachedBuffer(O.[[ViewedArrayBuffer]]) is true, return false.
	// 4. Let taRecord be MakeTypedArrayWithBufferWitnessRecord(O, unordered).
	// 5. NOTE: Bounds checking is not a synchronizing operation when O's backing buffer is a growable SharedArrayBuffer.
	let Some(buf_len) = buf.bytes(Ordering::Relaxed).map(|s| s.len()) else {
	return Ok(false);
	};
	Ok(inner.validate_index(index, buf_len).is_some())
	}

Note that you should put the spec as comment.

[AlvinThorn008]

@zhuzhu81998
That is true. I debated whether it was necessary but it's certainly more in line with the codebase's style. I'll refactor it in a couple minutes.

Thanks

[AlvinThorn008]

I've copied the format of the function you linked. Everything seems to be working as before.

[jedel1043]

I think it's better to put this in TypedArray, such that we can simplify the name to is_fixed_length just like ArrayBuffer.is_fixed_len()

[AlvinThorn008]

Makes sense. I'll do that shortly

[AlvinThorn008]

I ran into a small borrowing error but it resolved now.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,732	50,735	+3
Ignored	1,426	1,426	0
Failed	805	802	-3
Panics	0	0	0
Conformance	95.79%	95.79%	+0.01%

Fixed tests (3):

test/staging/built-ins/Reflect/preventExtensions/preventExtensions-variable-length-typed-arrays.js (previously Failed)
test/staging/built-ins/Object/preventExtensions/preventExtensions-variable-length-typed-arrays.js (previously Failed)
test/staging/built-ins/Object/seal/seal-variable-length-typed-arrays.js (previously Failed)

Tested main commit: 2437b6704c4315f6ec8f0766bf229fba23e0e61e
Tested PR commit: 28bf51bd7811a673eab6e538d17933e0eb9ad26c
Compare commits: 2437b67...28bf51b

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 59.75%. Comparing base (6ddc2b4) to head (28bf51b).
⚠️ Report is 919 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/builtins/typed_array/object.rs	88.88%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5262       +/-   ##
===========================================
+ Coverage   47.24%   59.75%   +12.50%     
===========================================
  Files         476      589      +113     
  Lines       46892    63413    +16521     
===========================================
+ Hits        22154    37890    +15736     
- Misses      24738    25523      +785     

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