[breaking-change]

(for syntax-extensions)

- Token variant identifiers have been converted to PascalCase for consistency with Rust coding standards
- Some free-functions in `syntax::token` have been converted to methods on `syntax::token::Token`:
    - `can_begin_expr`         -> `Token::can_begin_expr`
    - `close_delimiter_for`    -> `Token::get_close_delimiter`
    - `is_lit`                 -> `Token::is_lit`
    - `is_ident`               -> `Token::is_ident`
    - `is_path`                -> `Token::is_path`
    - `is_plain_ident`         -> `Token::is_plain_ident`
    - `is_lifetime`            -> `Token::is_lifetime`
    - `is_mutability`          -> `Token::is_mutability`
    - `to_binop`               -> `Token::to_binop`
    - `is_keyword`             -> `Token::is_keyword`
    - `is_any_keyword`         -> `Token:is_any_keyword`
    - `is_strict_keyword`      -> `Token::is_strict_keyword`
    - `is_reserved_keyword`    -> `Token::is_reserved_keyword`
    - `mtwt_token_eq`          -> `Token::mtwt_eq`
- `token::Ident` now takes an enum instead of a boolean for clarity
- `token::{to_string, binop_to_string}` were moved to `pprust::{token_to_string, binop_to_string}`

Some minor wording fixes to the Closures chapter; my brain tripped a few times when reading it, so I tried to come up with something a bit smoother. I’m not a native speaker, so please do review this critically.

This reverts commit c245c5bb.

Parallel code generation generates invalid code for librand, which is
caught by recent versions of binutils.

This reverts commit c245c5bb.

Parallel code generation generates invalid code for librand, which is
caught by recent versions of binutils.

We now instead use a fresh variable for expressions that diverge.

Closes #14973.
Closes #13847.

[Work in progress]

cc @nikomatsakis

This PR changes the signature of several methods from `foo(self, ...)` to `foo(&self, ...)`/`foo(&mut self, ...)`, but there is no breakage of the usage of these methods due to the autoref nature of `method.call()`s. This PR also removes the lifetime parameter from some traits (`Trait<'a>` -> `Trait`). These changes break any use of the extension traits for generic programming, but those traits are not meant to be used for generic programming in the first place. In the whole rust distribution there was only one misuse of a extension trait as a bound, which got corrected (the bound was unnecessary and got removed) as part of this PR.

I've kept the commits as small and self-contained as possible for reviewing sake, but I can squash them when the review is over.

See this [table] to get an idea of what's left to be done. I've already DSTified [`Show`][show] and I'm working on `Hash`, but bootstrapping those changes seem to require a more recent snapshot (#18259 does the trick)

r? @aturon 
cc #16918 

[show]: https://github.com/japaric/rust/commits/show
[table]: https://docs.google.com/spreadsheets/d/1MZ_iSNuzsoqeS-mtLXnj9m0hBYaH5jI8k9G_Ud8FT5g/edit?usp=sharing

Just to have it somewhere to point to. Updating it will not
automatically update the one on static.rust-lang.org.

We now instead use a fresh variable for expressions that diverge.

Closes #18218

Avoid O(n^2) performance by reconsidering the full set of obligations only when we are about to report an error (#18208). I found it is still important to consider the full set in order to make tests like `let x: Vec<_> = obligations.iter().collect()` work.

I think we lack the infrastructure to write a regression test for this, but when I did manual testing I found a massive reduction in type-checking time for extreme examples like those found in #18208 vs stage0.

f? @dotdash

Avoid O(n^2) performance by reconsidering the full set of obligations only when we are about to report an error (#18208). I found it is still important to consider the full set in order to make tests like `let x: Vec<_> = obligations.iter().collect()` work.

- shrink_to_fit example is now more clear by asserting the capacity value
- annotation [0, mid) changed for [0, mid]

This adds impls of Eq/Ord/PartialEq/PartialOrd/Show/Default to Arc<T>, and it
also removes the `Send + Sync` bound on the `Clone` impl of Arc to make it more
deriving-friendly. The `Send + Sync` requirement is still enforce on
construction, of course!

The goal here is to make it easier to add new platform definitions,
especially when the additions are programmatic (ie: in build scripts).

This adds impls of Eq/Ord/PartialEq/PartialOrd/Show/Default to Arc<T>, and it
also removes the `Send + Sync` bound on the `Clone` impl of Arc to make it more
deriving-friendly. The `Send + Sync` requirement is still enforce on
construction, of course!

This allows unboxed closures that reference free type/region parameters to be monomorphized correctly in trans.

It was necessary to make `ty_unboxed_closure` carry around a `Substs` to accomplish this.  Plumbing this through typeck revealed several areas where type/region parameters in unboxed closure types are possibly not being handled correctly.  Since my goal was just to fix trans, I decided to leave FIXME comments on areas that still need attention and seek feedback on the best way to clean them up, possibly as a follow-up PR.

Closes #16791

This adds a `Substs` field to `ty_unboxed_closure` and plumbs basic
handling of it throughout the compiler. trans now correctly
monomorphizes captured free variables and llvm function defs.  This
fixes uses of unboxed closures which reference a free type or region
parameter from their environment in either their signature or free
variables.  Closes #16791

This PR changes the signature of several methods from `foo(self, ...)` to
`foo(&self, ...)`/`foo(&mut self, ...)`, but there is no breakage of the usage
of these methods due to the autoref nature of `method.call()`s. This PR also
removes the lifetime parameter from some traits (`Trait<'a>` -> `Trait`). These
changes break any use of the extension traits for generic programming, but
those traits are not meant to be used for generic programming in the first
place. In the whole rust distribution there was only one misuse of a extension
trait as a bound, which got corrected (the bound was unnecessary and got
removed) as part of this PR.

[breaking-change]