The documentation states that this `ErrorKind` is not used by the
standard library. Instead, `io::ErrorKind::Uncategorized` should be
used.

This avoids toil when changing other functions in `ObligationForest` to take an `OUT` parameter.

In particular, this allows rustdoc to recover from cycle errors when normalizing associated types for documentation.

In the past, `@jackh726` has said we need to be careful about overflow errors:

> Off the top of my head, we definitely should be careful about treating overflow errors the same as
"not implemented for some reason" errors. Otherwise, you could end up with behavior that is
different depending on recursion depth. But, that might be context-dependent.

But cycle errors should be safe to unconditionally report; they don't depend on the recursion depth, they will always be an error whenever they're encountered.

…se-in-std, r=Mark-Simulacrum

Remove use of `io::ErrorKind::Other` in std

The documentation states that this `ErrorKind` is not used by the standard library. Instead, `io::ErrorKind::Uncategorized` should be used.

The two instances are in the unstable API [linux_pidfd](rust-lang#82971).

Make cycle errors recoverable

In particular, this allows rustdoc to recover from cycle errors when normalizing associated types for documentation.

In the past, ``@jackh726`` has said we need to be careful about overflow errors: rust-lang#91430 (comment)

> Off the top of my head, we definitely should be careful about treating overflow errors the same as
"not implemented for some reason" errors. Otherwise, you could end up with behavior that is
different depending on recursion depth. But, that might be context-dependent.

But cycle errors should be safe to unconditionally report; they don't depend on the recursion depth, they will always be an error whenever they're encountered.

Helps with rust-lang#81091.

r? ``@lcnr`` cc ``@matthewjasper``

…eholk

Always print '_, even for erased lifetimes.

Explicit lifetime arguments are now the recommended syntax in rust 2018 and rust 2021.  This PR applies this discipline to rustc itself.

…opaque, r=oli-obk

Skip `Equate` relation in `handle_opaque_type`

r? `@oli-obk`

…jackh726

rustc_transmute: fix big-endian discriminants

I noticed that some new tests were failing in Fedora on s390x only, which usually means there's a problem with big-endian, and sure enough there's a FIXME(`@jswrenn)` for that in `rustc_transmute`. This patch implements the appropriate consideration for target endianness, rather than using native (host) endian.

Fix a typo “pararmeter” in error message

Issue reported on IRLO: https://internals.rust-lang.org/t/fixing-a-typo/17427