v4.9.3

Highlights

Jint 4.9.3 is a maintenance release on top of 4.9.2 that closes the remaining test262 gaps from the 4.9.x line, hardens bulk built-ins against runaway inputs, and delivers large TypedArray performance gains. There are no public API surface changes, but host code that reads an error's stack should review the breaking-change note below, plus one additional minor behavioral note.

ECMAScript spec coverage

The bundled test262 suite was bumped to its latest snapshot and the spec gaps it surfaced were implemented — the full conformance suite now passes with 0 failures (#2489, #2490):

• Error.prototype.stack accessor (error-stack-accessor proposal) — stack is now a configurable get/set accessor on %Error.prototype% rather than an own data property on each instance. This is a breaking change for host (C#) code that reads stack — see the breaking-change note below.
• Immutable ArrayBuffer write rejection — %TypedArray%.prototype mutators (copyWithin / fill / reverse / set / sort), the Atomics read-modify-write ops, and Uint8Array setFromBase64 / setFromHex now throw TypeError before any observable side effect when the backing buffer is immutable.
• Intl legacy-constructor mode (normative-optional) for NumberFormat and DateTimeFormat, plus the new Intl.PluralRules compactDisplay option.
• Temporal.ZonedDateTime — rejects not-yet-adopted calendar annotations and correctly rounds to start-of-day when midnight occurs twice across a fall-back DST transition.
• Source-phase import re-exports — import source x from "…"; export { x }; is now supported (#2490).

Performance

• TypedArray bulk operations were rewritten around System.Array.Copy / Span<T> instead of per-element decode/encode loops. set, slice, copyWithin, with, fill, reverse, toReversed, and the indexOf / lastIndexOf / includes scans are now roughly 80×–350× faster with drastically lower allocations (#2488).

Robustness

• Bulk built-ins are now interruptible by execution constraints (#2487, fixes #2486). Operations such as 'x'.padStart(2147483647) or Array.from({ length: 50000000 }), along with the Array / %TypedArray% / RegExp / JSON / String bulk loops, now honor TimeoutInterval / MaxStatements / LimitMemory and raise a catchable RangeError instead of hanging or throwing an uncatchable OutOfMemoryException.

Correctness

• Custom regex engine: fixed flag v patterns that were incorrectly rejected (e.g. /-/v, /&&/v, /[\!]/v) (#2481).
• Corrected escaping of regexp patterns built at run-time via new RegExp(...), RegExp(...), .compile(...), String.prototype.match, etc. (#2482).

⚠️ Breaking change — reading an error's stack from host code

The Error.prototype.stack accessor change above also affects host (C#) code that inspects an error's stack trace. Previously stack was an own data property of every error instance, so an own-property read found the trace directly. It is now a get/set accessor defined on %Error.prototype% and is no longer an own property of the instance (#2489).

As a result, reading the trace with ObjectInstance.TryGetValue("stack", out var v) now yields undefined. TryGetValue still walks the prototype chain and finds the accessor on %Error.prototype%, but it invokes the inherited getter with the prototype as the receiver instead of the original error instance. The prototype has no [[ErrorData]] internal slot, so the getter returns undefined and the captured trace is lost.

Read the value through the accessor-aware Get, which threads the correct receiver:

// before — now returns undefined
errorObject.TryGetValue("stack", out var stack);

// after — invokes the getter with the error instance as the receiver
var stack = errorObject.Get("stack");

⚠️ Minor behavioral change

For .NET Regex objects exposed to the engine, JsRegExp.Source / ToString() now return the placeholder ?[native regex] instead of the raw .NET pattern — the .NET pattern was misleading because it isn't a valid JS pattern (#2482).

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What's Changed

• Fix flag v bugs in custom regex engine by @adams85 in #2481
• Correct escaping of regexp patterns created at run-time by @adams85 in #2482
• Bump the all-dependencies group with 5 updates by @dependabot[bot] in #2485
• Make bulk built-ins interruptible by execution constraints (#2486) by @lahma in #2487
• Optimize TypedArray bulk operations with Span/Array.Copy by @lahma in #2488
• Update test262 suite and implement newly-surfaced features by @lahma in #2489
• Support re-exporting source-phase imports by @lahma in #2490

Full Changelog: v4.9.2...v4.9.3