Follow-up for
rust-lang#119477 (comment)

- lint if the lock was in a nested pattern
- lint if the lock is inside a `Result<Lock, _>`

This shortens the `#[must_use]` diagnostics displayed, in light of the [review comment](https://github.com/rust-lang/rust/pull/62431/files#r300819839) on when this was originally added.

We have several methods indicating the presence of errors, lint errors,
and delayed bugs. I find it frustrating that it's very unclear which one
you should use in any particular spot. This commit attempts to instill a
basic principle of "use the least general one possible", because that
reflects reality in practice -- `has_errors` is the least general one
and has by far the most uses (esp. via `abort_if_errors`).

Specifics:
- Add some comments giving some usage guidelines.
- Prefer `has_errors` to comparing `err_count` to zero.
- Remove `has_errors_or_span_delayed_bugs` because it's a weird one: in
  the cases where we need to count delayed bugs, we should really be
  counting lint errors as well.
- Rename `is_compilation_going_to_fail` as
  `has_errors_or_lint_errors_or_span_delayed_bugs`, for consistency with
  `has_errors` and `has_errors_or_lint_errors`.
- Change a few other `has_errors_or_lint_errors` calls to `has_errors`,
  as per the "least general" principle.

This didn't turn out to be as neat as I hoped when I started, but I
think it's still an improvement.

…_field, r=Nilstrieb

 Explanation that fields are being used when deriving `(Partial)Ord` on enums

When deriving `std::cmp::Ord` or `std::cmp::PartialOrd` on enums, their fields are compared if the variants are equal.
This means that the last assertion in the following snipped panics.
```rust
use std::cmp::{PartialEq, Eq, PartialOrd, Ord};

#[derive(PartialEq, Eq, PartialOrd, Ord)]
enum Sizes {
    Small(usize),
    Big(usize),
}

fn main() {
    let a = Sizes::Big(3);
    let b = Sizes::Big(5);
    let c = Sizes::Small(10);
    assert!( c < a);
    assert_eq!(a, c);
}
```

This is more often expected behavior than not, and can be easily circumvented, as discussed in [this thread](https://users.rust-lang.org/t/how-to-sort-enum-variants/52291/4).
But it is addressed nowhere in the documentation, yet.
So I stumbled across this, as I personally did not expect fields being used in `PartialOrd`.
I added the explanation to the documentation.

Improve `let_underscore_lock`

- lint if the lock was in a nested pattern
- lint if the lock is inside a `Result<Lock, _>`

addresses rust-lang#119704 (comment)

…lstrieb

Tweak Library Integer Division Docs

Improved the documentation and diagnostics related to panicking in the division-like methods in std:

* For signed methods that can overflow, clarified "results in overflow" to "self is -1 and rhs is Self::MIN." This is more concise than saying "results in overflow" and then explaining how it could overflow.
* For floor/ceil_div, corrected the documentation and made it more like the documentation in other methods.
* For signed methods that can overflow, explicitly mention that they are not affected by compiler flags.
* Removed all unused rustc_inherit_overflow_checks attributes. The non-division-like operations will never overflow.
* Added track_caller attributes to all methods that can panic. The panic messages will always be correct. For example, division methods all have / before %.
* Edited the saturating_div documentation to be consistent with similar methods.

…odals, r=fmease

rustdoc: hide modals when resizing the sidebar

Follow-up for
rust-lang#119477 (comment)

CC `@lukas-code`

…compiler-errors,oli-obk

Fix error counting

There is some messiness in how errors get counted. Here are some cleanups.

r? `@compiler-errors`

…-option-must-use, r=Nilstrieb

Shorten `#[must_use]` Diagnostic Message for `Option::is_none`

This shortens the `#[must_use]` diagnostics displayed, in light of the [review comment](https://github.com/rust-lang/rust/pull/62431/files#r300819839) on when this was originally added.

…link, r=dtolnay

Correct the anchor of an URL in an error message

Following error message from rustc points to a URL, but its anchor does not exist.
The destination seems to be https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-link-lib.
This PR makes that correction.

      = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)

…ler-errors

Replace `#!/bin/bash` with `#!/usr/bin/env bash` in rust-installer tests

This allows the rust-installer tests to pass on NixOS

This change has [already been made](rust-lang@302ad21) for the actual installer, it appears that the tests were just forgotten.

…r=compiler-errors

Give nnethercote more reviews

Gulp!