This is logically equivalent to the previous code.

Actually empty matches are still handled by a different code path

This uses the exact same code path that would be used for
`match x { _ if false => {} }`, since in both cases the resulting matrix
is empty. Since we think the behaviour in that case is ok, then we can
remove the special case and use the default code path.

When the feature is on, the special casing is not needed. That way when
we stabilize the feature this `if` can just be removed.

…t().assume_init()

Fix a minor typo

… r=varkor,Centril,estebank

Improve diagnostics and code for exhaustiveness of empty matches

There was a completely separate check and diagnostics for the case of an empty match. This led to slightly different error messages and duplicated code.
This improves code reuse and generally clarifies what happens for empty matches. This also clarifies the action of the `exhaustive_patterns` feature, and ensures that this feature doesn't change diagnostics in places it doesn't need to.

…drAus

VecDeque: drop remaining items on destructor panic

Closes rust-lang#67232

dont ICE in case of invalid drop fn

Fixes rust-lang/miri#1112

r? @oli-obk

Reduce allocs for validation errors

This probably doesn't really matter, but I just felt like I had to do this...

r? @oli-obk

be explicit that mem::uninitialized is the same as MaybeUninit::uninit().assume_init()

Cc @Centril @nikomatsakis

`coerce_inner`: use initial `expected_ty`

Fixes rust-lang#67273.
Follow-up to rust-lang#59439.

r? @oli-obk

docs: std::convert::From: Fix typo

Fix a minor typo