Provenance tracking issues

[MaulingMonkey]

core::ptr::from_raw_parts is not yet stable

• Tracking Issue for pointer metadata APIs rust-lang/rust#81513

Which is a problem for here:

thindx-xaudio2/crates/thindx-xaudio2/src/xa28/ixaudio2sourcevoice_ext.rs

Lines 57 to 75 in 8b77f0e

	b.pContext = Box::into_raw(Box::new(SourceBuffer::<Context> {
	context,
	audio_len: audio_data.len(),
	audio_data: {
	// ⚠️ WARNING: easy to muck up provenance of ArcInner<[Sample]> here.
	let raw : *const [Sample] = Arc::into_raw(audio_data);
	let raw : *const Sample = unsafe { (*raw).as_ptr() };
	raw.cast()
	},
	audio_free: |data, len| {
	// 🐞 BUG: core::slice::from_raw_parts here incorrectly narrows provenance from ArcInner<[Sample]> to [Sample] here.
	// However, core::ptr::from_raw_parts is not yet stable: https://github.com/rust-lang/rust/issues/81513
	// Local tracking issue: https://github.com/MaulingMonkey/thindx-xaudio2/issues/18
	let audio_data : *const [Sample] = unsafe { core::slice::from_raw_parts(data as *const Sample, len) };
	let audio_data = unsafe { Arc::from_raw(audio_data) };
	drop(audio_data);
	},
	})).cast();