Co-Authored-By: Alexander Regueiro <alexreg@me.com>

Co-authored-by: Alexander Regueiro <alexreg@me.com>

Co-authored-by: Alexander Regueiro <alexreg@me.com>

`TokenStream::Stream` can represent a token stream containing any number
of token trees. `TokenStream::Tree` is the special case representing a
single token tree. The latter doesn't occur all that often dynamically,
so this commit removes it, which simplifies the code quite a bit.

This change has mixed performance effects.

- The size of `TokenStream` drops from 32 bytes to 8 bytes, and there
  is one less case for all the match statements.

- The conversion of a `TokenTree` to a `TokenStream` now requires two
  allocations, for the creation of a single element Lrc<Vec<_>>. (But a
  subsequent commit in this PR will reduce the main source of such
  conversions.)

`TokenStream` is now almost identical to `ThinTokenStream`. This commit
removes the latter, replacing it with the former.

This avoids some allocations.

Because that's the more typical way of representing an all-or-nothing
type.

This requires restructuring things a little so that there is only one
callsite, ensuring that inlinining doesn't cause unnecessary code bloat.

This reduces instruction counts for the `unicode_normalization`
benchmark by up to 4%.

…re, r=petrochenkov

Simplify `TokenStream` some more

These commits simplify `TokenStream`, remove `ThinTokenStream`, and avoid some clones. The end result is simpler code and a slight perf win on some benchmarks.

r? @petrochenkov

…nikomatsakis

make trait-aliases work across crates

This is rebase of a small part of @alexreg's PR rust-lang#55994. It focuses just on the changes that integrate trait aliases properly into crate metadata, excluding the stylistic edits and the trait objects.

The stylistic edits I also rebased and can open a separate PR.

The trait object stuff I found challenging and decided it basically needed to be reimplemented. For now I've excluded it.

Since this is really @alexreg's work (I really just rebased) I am going to make it r=me once it is working.

Fixes rust-lang#56488.
Fixes rust-lang#57023.

Add missing unpretty option help message

There are some missing help messages that is printed `ructc -Zunpretty help` and receiving invalid option.

related with rust-lang#16419, rust-lang#45721, rust-lang#21085, rust-lang#31916

privacy: Account for associated existential types

Turns out they *can* be associated (but only in impls, not traits).
Fixes rust-lang#53546 (comment)

r? @arielb1

…xcrichton

Fix release manifest generation

r? @alexcrichton

…enkov

add applicability to remaining suggestions

Fixes rust-lang#50723.

I noticed that the suggestion methods on `DiagnosticBuilder` weren't actually deprecated due to rust-lang#57679. This PR deprecates them properly and fixes the remaining usages.

There's also a PR for clippy at rust-lang/rust-clippy#3667.

…=nikomatsakis

Tweak `expand_node`

These commits speed up the `unicode_normalization` benchmark a little.