…rties are ensured by default impls

These were changed in rust-lang#84703.

Co-authored-by: Jane Lusby <[email protected]>

The `RustdocGUI::should_run` condition spawns `npm list` several times
which adds up to seconds of wall-time.
Evaluate the condition lazily to to keep `./x.py test tidy` and similar
short-running tasks fast.

This was unsound since a panic in a.next_back() would result in the
length not being updated which would then lead to the same element
being revisited in the side-effect preserving code.

Account for bad placeholder errors on consts/statics with trait objects

Fixes rust-lang#75889
r? `@estebank`

document PartialEq, PartialOrd, Ord requirements more explicitly

This is the result of discussion in rust-lang#50230, in particular [this summary comment](rust-lang#50230 (comment)).

Fixes rust-lang#50230.

…Simulacrum

Lazify is_really_default condition in the RustdocGUI bootstrap step

The `RustdocGUI::should_run` condition spawns `npm list` several times which adds up to seconds of wall-time.
Evaluate the condition lazily to to keep `./x.py test tidy` and similar short-running tasks fast.

Fixes rust-lang#86147

…ulacrum

Fix a bug in the linkchecker

There was a small typo in the linkchecker (in rust-lang#85652) that caused it to report a `#` fragment link error pointing to the wrong file (it was displaying the path to the source file, not the target of the link).

This also includes a few other changes:
- Fixes the tests due to some changes in the redirect handling in rust-lang#84703.
- Adds the tests to rustbuild to run whenever the linkchecker itself is run.
- Updates the tests to validate more of the output (so that a mistake like this would have been caught).

Closes rust-lang#86144

Specify the kind of the item for E0121

Fixes rust-lang#86005

…, r=Mark-Simulacrum

Updated release note

close rust-lang#77098

base on rust-lang#78690

fix panic-safety in specialized Zip::next_back

This was unsound since a panic in a.next_back() would result in the
length not being updated which would then lead to the same element
being revisited in the side-effect preserving code.

fixes rust-lang#86443

…r=petrochenkov

Do not set depth to 0 in fully_expand_fragment

Fixes rust-lang#84632.

expand: Move some more derive logic to rustc_builtin_macros

And cleanup some `unwrap`s in `cfg_eval`.

Refactorings extracted from rust-lang#83354 and rust-lang#86057.
r? `@Aaron1011`