An initial refactoring before working on rust-lang#61809.

This moves the whole block into a method so that it can be reused in the
annotate-snippet output. It's already used in the new emitter, but
there's no UI tests with suggestions included in this PR.

A first look at some UI tests with suggestions showed that there's some
more work to do in [annotate-snippet-rs][annotate-snippet-rs] before the
new output is closer to the current one.

This avoids needlessly creating and threading the buffers through when
we only use them once.

This means that callers can pass in a closure like
`|buf| some_function(..., &mut buf)` and pass in arbitrary arguments to
that function without complicating the trait definition. We also keep
the impl for str and String, since it's useful to be able to just pass
in "" or format!("{}"...) results in some cases.

This changes Print's definition to take self, instead of &self, because
otherwise FnOnce cannot be called directly. We could instead take FnMut
or even Fn, but that seems like it'd merely complicate matters -- most
of the time, the FnOnce does not constrain us at all anyway. If it does,
a custom Print impl for &'_ SomeStruct is not all that painful.

Fix `window.hashchange is not a function`

Closes rust-lang#63707.

…GuillaumeGomez

Rustdoc: formatting to buffers

This should be reviewed commit-by-commit.

I've not attempted to fully flesh out what the end state of this PR could look like yet as I wanted to get it up for some early feedback (I already think this has some wins, too, so we could land it as-is).

The primary idea with `Buffer` is that it internally tracks whether we're printing to HTML or text, and the goal is that eventually instead of branch on `fmt.alternate()` anywhere, we'd call a helper like `buf.nbsp()` which would either return ` ` or ` ` depending on the target we're printing to. Obviously, that's not included in this PR, in part because it was already getting quite big.

Emit a single error on if expr with expectation and no else clause

Fix rust-lang#60254.

r? @Centril

…ntril

Account for arbitrary self types in E0599

Fix rust-lang#62373

…bank

librustc_errors: Extract sugg/subst handling into method

An initial refactoring before working on rust-lang#61809.

This moves the whole block into a method so that it can be reused in the
annotate-snippet emitter. The method is already used in the new emitter, but
there's no UI tests with suggestions included in this PR.

A first look at some UI tests with suggestions showed that there's some
more work to do in [annotate-snippet-rs][annotate-snippet-rs] before the new output is closer to the
current one, so I opted to do that in a second step.

r? @estebank

[annotate-snippet-rs]: https://github.com/rust-lang/annotate-snippets-rs

Fix const_err with `-(-0.0)`

Fixes rust-lang#64059

r? @oli-obk

use just one name when parameters and fields are the same

…ark-Simulacrum

Fix regex replacement in theme detection

Fixes rust-lang#64061.

This is sadly a lot of bad luck: after making the changes and re-build the docs, I just forgot to force reload the page. Hence having the old (working) version with two replacements instead of the failing regex. Sorry again about that...

cc @fenhl
r? @Mark-Simulacrum

…e, r=estebank

Emit error on intrinsic to fn ptr casts

I'm not sure if a type error is the best way of doing this but it seemed like a relatively correct place to do it, and I expect this is a pretty rare case to hit anyway.

Fixes rust-lang#15694