…oo one day

Fixes: rust-lang#84561

On bootstrap the IntoIterator trait is not implemented
yet for arrays.

Searching for "reduce" currently puts the `reduce` alias for `fold`
above the actual `reduce` function. The `reduce` function already has a
cross-reference for `fold`, and vice versa.

Each label needs to be separated by a comma (see the ICE issue template
for an example of correct usage).

As a result of this problem, the `regression-untriaged` label has not
been automatically added to issues opened with this template.

See c127530 for another example of this.

…rent process

This is a straightforward wrapper that uses the existing helpers for C
string handling and errno handling.

Having this available is convenient for UNIX utility programs written in
Rust, and avoids having to call the unsafe `libc::chroot` directly and
handle errors manually, in a program that may otherwise be entirely safe
code.

Use flex more consistently

Builds on rust-lang#84376, related to rust-lang#84354.

- Fully replaces `float: right` with `flex` on `.content .out-of-band`.
- Uses `flex` more consistently with existing usage (on `h3`, `h4`, etc.).

Tested on various widths to make sure the pages behave as before.

Vastly improves coverage spans for macros

Fixes: rust-lang#84561

This resolves problems where macros like `trace!(...)` would show zero coverage if tracing was disabled, and `assert_eq!(...)` would show zero coverage if the assertion did not fail, because only one coverage span was generated, for the branch.

This PR started with an idea that I could just drop branching blocks with same span as expanded macro. (See the fixed issue for more details.)

That did help, but it didn't resolve everything.

I also needed to add a span specifically for the macro name (plus `!`) to ensure the macro gets coverage even if it's internal expansion adds conditional branching blocks that are retained, and would otherwise drop the outer span. Now that outer span is _only_ the `(argument, list)`, which can safely be dropped now), because the macro name has its own span.

While testing, I also noticed the spanview debug output can cause an ICE on a function with no body. The
workaround for this is included in this PR (separate commit).

r? ````@tmandry````
cc? ````@wesleywiser````

Point out that behavior might be switched on 2015 and 2018 too one day

Reword documentation to make it clear that behaviour can be switched on older editions too, one day in the future. It doesn't *have* to be switched, but I think it's good to have it as an option and re-evaluate it a few months/years down the line when e.g. the crates that showed up in crater were broken by different changes in the language already.

cc rust-lang#25725, rust-lang#65819, rust-lang#66145, rust-lang#84147 , and rust-lang#84133 (comment)

…r=nikomatsakis

Don't rebind in `transitive_bounds_that_define_assoc_type`

Fixes rust-lang#83737
Fixes rust-lang#84604

Also fixes another issue that I don't have a test for, popped up in [zulip](https://rust-lang.zulipchat.com/#narrow/stream/144729-wg-traits/topic/Duplicate.20symbol.20error.20.2384604/near/236570445)

r? ``@nikomatsakis``

…vink

Minor grammar tweaks for readability to btree internals

I was reading through the btree implementation and I noticed some grammar that could be improved in Node.rs so here is what I think would be a minor improvement.

…ss-for-search-results, r=Nemo157

Remove unnecessary CSS rules for search results

Discovered that this was useless when working on rust-lang/docs.rs#1382.

r? `````@Nemo157`````

…in-search-results, r=Nemo157

Remove unneeded bottom margin on search results

As you can see, there is still more than enough space at the bottom:

![Screenshot from 2021-04-29 11-26-57](https://user-images.githubusercontent.com/3050060/116530090-ea797800-a8dd-11eb-8eef-2288cf68e0d2.png)

r? ```@Nemo157```

…lett

make feature recommendations optional

this is what we're already doing for other feature gates, so it's better to be consistent

Drop alias `reduce` for `fold` - we have a `reduce` function

Searching for "reduce" currently puts the `reduce` alias for `fold`
above the actual `reduce` function. The `reduce` function already has a
cross-reference for `fold`, and vice versa.

…te, r=Mark-Simulacrum

Fix labels for regression issue template

Each label needs to be separated by a comma (see the ICE issue template
for an example of correct usage).

As a result of this problem, the `regression-untriaged` label has not
been automatically added to issues opened with this template.

See c127530 for another example of this.

r? ``@Mark-Simulacrum``

Add std::os::unix::fs::chroot to change the root directory of the current process

This is a straightforward wrapper that uses the existing helpers for C
string handling and errno handling.

Having this available is convenient for UNIX utility programs written in
Rust, and avoids having to call the unsafe `libc::chroot` directly and
handle errors manually, in a program that may otherwise be entirely safe
code.