Fixes rust-lang#54302.

There is no reason not to do it.

This makes evaluation more consistent with fulfillment.

I noticed a small typo while reading over this document.

In  rust-lang#51833, I improved the performance of `copy_undef_mask()`. As such, the old FIXME wasn't appropriate anymore. The main remaining thing left to do is to implement a fast path for non-overlapping copies (per @oli-obk).

Joshua Netterfield reported an ICE when the unused-parentheses lint
triggered around an async block (rust-lang#54752). In order to compose an
autofixable suggestion, the lint invokes the pretty-printer on the
unnecessarily-parenthesized expression. (One wonders why the lint
doesn't just use `SourceMap::span_to_snippet` instead, to preserve the
formatting of the original source?—but for that, you'd have to ask the
author of 5c9f806.)

But then the pretty-printer panics when trying to call `<pprust::State
as PrintState>::end` when `State.boxes` is empty. Empirically, the
problem would seem to be solved if we start some "boxes" beforehand in
the `ast::ExprKind::Async` arm of the big match in
`print_expr_outer_attr_style`, exactly like we do in the
immediately-preceding match arm for `ast::ExprKind::Block`—it would
seem pretty ("pretty") reasonable for the pretty-printing of async
blocks to work a lot like the pretty-printing of ordinary non-async
blocks, right??

Of course, it would be shamefully cargo-culty to commit code on the
basis of this kind of mere reasoning-by-analogy (in contrast to
understanding the design of the pretty-printer in such detail that the
correctness of the patch is comprehended with all the lucid certainty
of mathematical proof, rather than being merely surmised by
intuition). But maybe we care more about fixing the bug with high
probability today, than with certainty in some indefinite hypothetical
future?  Maybe the effort is worth a fifth of a shirt??

Humbly resolves rust-lang#54752.

Fixes rust-lang#52187.

…ror, r=GuillaumeGomez

Add doc for impl From for Std Error

As part of issue rust-lang#51430 (cc @skade).

I am not sure if it is going to a correct direction so put up here so that people can comment.

…tsakis

handle outlives predicates in trait evaluation

This handles higher-ranked outlives predicates in trait evaluation the same way they are handled in projection.

Fixes rust-lang#54302. I think this is a more correct fix than rust-lang#54401 because it fixes the root case in evaluation instead of making evaluation used in less cases. However, we might want to go to a direction closer to @nikomatsakis's solution with Chalk.

r? @nikomatsakis

…tion, r=varkor

Fix range literals borrowing suggestions

Fixes rust-lang#54505. The compiler issued incorrect range borrowing suggestions (missing `()` around borrows of range literals). This was not correct syntax (see the issue for an example).

With changes in this PR, this is fixed for all types of `Range` literals.

Thanks again to @varkor and @estebank for their invaluable help and guidance.

r? @varkor

Make spec_extend use for_each()

`for_each` will use an iterator's own implementation of `try_fold`, which I understand to be generally preferable (because nested iterator adapter's will use each other's `try_fold` and be designed for the specific adaptation in a way that promotes performance and inlining.

Fix typo in CONTRIBUTING.md

I noticed a small typo while reading over this document.

…i-obk

Update a FIXME in memory.rs

In  rust-lang#51833, I improved the performance of `copy_undef_mask()`. As such, the old FIXME wasn't appropriate anymore. The main remaining thing left to do is to implement a fast path for non-overlapping copies (per @oli-obk).

r? @oli-obk

…ertj

abolish ICE when pretty-printing async block

@jnetterf reported an ICE when the unused-parentheses lint triggered around an async block (rust-lang#54752). In order to compose an autofixable suggestion, the lint invokes the pretty-printer on the unnecessarily-parenthesized expression. (One wonders why the lint doesn't just use `SourceMap::span_to_snippet` instead, to preserve the formatting of the original source?—but to answer that, you'd have to ask the author of 5c9f806.)

But then the pretty-printer panics when trying to call `<pprust::State as PrintState>::end` when `State.boxes` is empty. Empirically, the problem would seem to be solved if we start some "boxes" beforehand in the `ast::ExprKind::Async` arm of the big match in `print_expr_outer_attr_style`, exactly like we do in the immediately-preceding match arm for `ast::ExprKind::Block`—it would seem pretty ("pretty") reasonable for the pretty-printing of async blocks to work a lot like the pretty-printing of ordinary non-async blocks, right??

Of course, it would be shamefully cargo-culty to commit code on the basis of this kind of mere reasoning-by-analogy (in contrast to understanding the design of the pretty-printer in such detail that the correctness of the patch is comprehended with all the lucid certainty of mathematical proof, rather than being merely surmised by intuition). But maybe we care more about fixing the bug with high probability today, than with certainty in some indefinite hypothetical future?  Maybe the effort is worth [a fifth of a shirt](https://hacktoberfest.digitalocean.com/stats/zackmdavis)??

Humbly resolves rust-lang#54752.

r? @cramertj

Remove duplicate predicates in `explicit_predicates_of`

I took a more brutal approach than described in rust-lang#52187. I could have used the `linked_hash_map` crate but this seems overkill, especially as we need a vec storage in the end.

r? @nikomatsakis

A handful of cleanups for rustc/mir

- use the "regular" `into()` instead of `graphviz::IntoCow` in `mod.rs`
- `format!("{}", x)` > `x.to_string()`
- remove one unnecessary `String` allocation
- shorten the logic of one loop
- `assert!(x == y)` > `assert_eq!(x, y)`
- whitespace & formatting fixes

r? @oli-obk

Introduce `TyKind::UnnormalizedProjection`

Introduce a new variant used for lazy normalization in chalk integration. Mostly `bug!` everywhere.

r? @nikomatsakis