add ui test

compute enclosing_scope_span on demand

add scope test

make tidy happy

stylistic and typo fixes

The exact same logic was used in check_arms and check_match to build the
matrix of relevant patterns. It would actually probably have been a bug
if it was not the case, since exhaustiveness checking should be the same
as checking reachability of an additional `_ => ...` match branch.

We want the lifetimes of the patterns contained in the matrix and the
candidate `PatStack` to be the same so that they can be mixed together.
A lot of this would not be necessary if `SmallVec` was covariant in its
type argument (see servo/rust-smallvec#146).

Also remove a couple of redundant `visit_mac` asserts

…er_tokens`.

Show the sign for signed ops on `exact_div`

r? @RalfJung Cc https://github.com/rust-lang/miri/pull/961/files#r341842128

I'm fairly unhappy with the duplication and the general effort required for this.

Maybe it would be better to add a `display` impl for `ImmTy`?

…=davidtwco

Add `enclosing scope` parameter to `rustc_on_unimplemented`

Adds a new parameter to `#[rustc_on_unimplemented]`, `enclosing scope`, which highlights the function or closure scope with a message.

The wip part refers to adding this annotation to `Try` trait to improve ergonomics (which I don't know how to do since I change both std and librustc)

Closes rust-lang#61709.

Adding docs for keyword match, move

Partial fix of issue rust-lang#34601.

syntax: Unify macro and attribute arguments in AST

The unified form (`ast::MacArgs`) represents parsed arguments instead of an unstructured token stream that was previously used for attributes.
It also tracks some spans and delimiter kinds better for fn-like macros and macro definitions.

I've been talking about implementing this with @nnethercote in rust-lang#65750 (comment).
The parsed representation is closer to `MetaItem` and requires less token juggling during conversions, so it potentially may be faster.

r? @Centril

Remove `ord` lang item

At this point it seems to be unused, and just `partial_ord` is used instead. This removes the unused lang item.

Remove hack for top-level or-patterns in match checking

Follow-up to rust-lang#66612.

Or-patterns are now truly first-class in match checking. As a side-effect, redundant subpatterns are linted as such, making the `unreachable_patterns` lint a bit more general.

cc rust-lang#54883

r? @varkor