Commit1862054

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Describe Sized requirements for mem::offset_of

The container doesn't have to be sized, but the field must be sized (atleast untilrust-lang#126151 is stable).

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Original file line number	Diff line number	Diff line change
`@@ -1266,6 +1266,20 @@ impl<T> SizedTypeProperties for T {}`
`1266`	`1266`	/// // ^^^ error[E0616]: field `private` of struct `Struct` is private
`1267`	`1267`	/// ```
`1268`	`1268`	`///`
	`1269`	+/// Only [`Sized`] fields are supported, but the container may be unsized:
	`1270`	+/// ```
	`1271`	`+/// # use core::mem;`
	`1272`	`+/// #[repr(C)]`
	`1273`	`+/// pub struct Struct {`
	`1274`	`+/// a: u8,`
	`1275`	`+/// b: [u8],`
	`1276`	`+/// }`
	`1277`	`+///`
	`1278`	`+/// assert_eq!(mem::offset_of!(Struct, a), 0); // OK`
	`1279`	`+/// // assert_eq!(mem::offset_of!(Struct, b), 1);`
	`1280`	`+/// // ^^^ error[E0277]: doesn't have a size known at compile-time`
	`1281`	+/// ```
	`1282`	`+///`
`1269`	`1283`	`/// Note that type layout is, in general, [subject to change and`
`1270`	`1284`	`/// platform-specific](https://doc.rust-lang.org/reference/type-layout.html). If`
`1271`	`1285`	/// layout stability is required, consider using an [explicit `repr` attribute].

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