Tracking issue for RFC 2043: Add `align_offset` intrinsic (formerly: and `[T]::align_to` function)

[aturon]

This is a tracking issue for the RFC "Add align_offset intrinsic and [T]::align_to function " (rust-lang/rfcs#2043). align_to is stable, so this tracks just align_offset now.

Steps:

• Implement the RFC (align_offset: Add align_offset intrinsic #43903; align_to: Implement [T]::align_to #50319)
• Adjust documentation (see instructions on forge)
• Stabilization PR (see instructions on forge): align_to: stabilize slice_align_to #53754

Unresolved questions:

• "produce a lint in case sizeof<T>() % sizeof<U>() != 0 and in case the expansion is not part of a monomorphisation, since in that case align_to is statically known to never be effective

[SimonSapin]

@oli-obk Is it useful to stabilize align_offset before align_to is implemented?

[oli-obk]

Generally yes, because that's the key feature. Align_to is just convenience

[SimonSapin]

Alright, then. Let’s stabilize align_offset and leave this issue open for tracking align_to.

@rfcbot fcp merge