fix(engine): replace JsRegExp js_expect with proper error handling

[tkshsbcue]

fix(engine): replace JsRegExp js_expect with proper error handling

Summary

Replaces all js_expect() and expect() calls in the JsRegExp Rust API wrapper with proper JsResult-based error handling. The JsRegExp type is used by applications that embed Boa; previously, invariant violations would panic and crash the host process instead of returning recoverable errors.

Motivation

When Boa is embedded in a Rust application (e.g. via boa_engine), the JsRegExp API is the primary way to create and interact with RegExp objects from Rust. Methods like JsRegExp::new(), .global(), .test(), .exec(), etc. used js_expect() on the assumption that internal RegExp getters always return the expected types (boolean, string, object). If an invariant is ever violated—due to a bug, corrupted state, or future refactor—the host process panics. For embedded use cases, this is unacceptable: the embedder expects to handle errors via Result and continue execution. Replacing panics with proper JsResult propagation ensures the API is robust and embedder-friendly.

Changes

Category	Description
Removed	JsExpect import from jsregexp.rs
Replaced	js_expect("...") with `ok_or_else(
Replaced	to_object(context).js_expect(...) and JsArray::from_object(...).js_expect(...) with ? for exec()
Added	JsError import for explicit error construction

Methods updated:

• new() — as_object().js_expect → ok_or_else with JsError::from
• has_indices(), global(), ignore_case(), multiline(), dot_all(), unicode(), sticky() — as_boolean().js_expect → ok_or_else
• flags(), source(), to_string() — as_string().js_expect → ok_or_else
• test() — as_boolean().js_expect → ok_or_else
• exec() — to_object().js_expect and from_object().js_expect → ? (propagate JsResult)

Technical Details

• File modified: core/engine/src/object/builtins/jsregexp.rs
• Lines changed: +73, -32
• Behavioral impact: Invariant violations that previously panicked now return Err(JsError) with a TypeError message. Normal operation is unchanged; all existing tests pass.

The ok_or_else pattern converts Option<T> to Result<T, JsError> by constructing a JsNativeError::typ() with a descriptive message when the value is None. For exec(), to_object() and JsArray::from_object() already return JsResult, so ? is used to propagate errors.

Testing

• cargo test -p boa_engine --lib — all 930 tests pass
• cargo clippy -p boa_engine — no warnings
• cargo build — successful compilation

[tkshsbcue]

@jedel1043 i hope you can have a look
thanks!

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	49,666	49,666	0
Ignored	2,284	2,284	0
Failed	1,013	1,013	0
Panics	0	0	0
Conformance	93.77%	93.77%	0.00%

Tested main commit: 2ebc979e4492a12a5361b9aaeb727183e1d25462
Tested PR commit: 418b97766a86dcef853f76e232b60713500485f1
Compare commits: 2ebc979...418b977

[codecov]

Codecov Report

❌ Patch coverage is 7.31707% with 38 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.76%. Comparing base (6ddc2b4) to head (418b977).
⚠️ Report is 773 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/object/builtins/jsregexp.rs	7.31%	38 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4915       +/-   ##
===========================================
+ Coverage   47.24%   57.76%   +10.51%     
===========================================
  Files         476      556       +80     
  Lines       46892    60793    +13901     
===========================================
+ Hits        22154    35116    +12962     
- Misses      24738    25677      +939     

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