JSTypedArray: annotate swjs_create_typed_array for bounds-safety by airspeedswift · Pull Request #749 · swiftwasm/JavaScriptKit

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On recent clang/Swift toolchains, bounds-safety annotations on `void *`
parameters cause the Swift importer to synthesize an
`UnsafeRawBufferPointer`-taking overload alongside the original. Adding
these annotations to `swjs_create_typed_array` gives us that overload
for free, and it lays the foundation for broader `Span` adoption in
JavaScriptKit in follow-up PRs.

Because `elements_ptr` is `void *`, the byte count is
`length * sizeof(element)`. This PR adds a trailing `element_size`
parameter and annotates `elements_ptr` as
`__sized_by_or_null(length * element_size) __noescape`. Both annotations
are correct given the JS implementation: it constructs a typed array view
over WASM linear memory at `elementsPtr` with `length` elements and
immediately calls `.slice()` to copy before returning. The view
constructor reads exactly `length * constructor.BYTES_PER_ELEMENT` bytes,
which equals `length * element_size` since Swift passes
`MemoryLayout<Element>.stride` — matching `BYTES_PER_ELEMENT` for every
`TypedArrayElement` type. And because only the `.slice()` copy is
retained and returned, `elementsPtr` never escapes the call.
`__sized_by_or_null` rather than `__sized_by` preserves the existing
nullable contract: Swift's `Array.baseAddress` is `nil` for empty arrays,
and the JS side already handles `length == 0` without dereferencing the
pointer.

The macros are defined by clang's `<ptrcheck.h>` and `<lifetimebound.h>`
resource headers, both included explicitly: Apple's `<sys/cdefs.h>` pulls
in `<ptrcheck.h>` transitively, but Linux's does not, so direct inclusion
is required for cross-platform consistency.

The only coordinated change is in `JSTypedArray.swift`'s `createTypedArray`,
which passes `Int32(MemoryLayout<Element>.stride)` as the new argument;
the JS dispatch entry is unchanged — extra WASM arguments are silently
dropped.