At first, you might think, "Why not just click through to the aliased
type?" But, if a type alias instantiates all of the generic parameters
of the aliased type, then it can show layout info even though the
aliased type cannot (because we can't compute layout for generic types).
So, I think it's useful to show layout info for type aliases.

This is a followup of 78d4b453ad2e19d44011b26fc55c949bff5dba3d
(originally part of rust-lang#83501).

This commit does the following.
- Expands on some of the things already mentioned in comments.
- Describes the uniqueness assumption, which is critical but wasn't
  mentioned at all.
- Rewrites `empty()` into a clearer form, as provided by Daniel
  Henry-Mantilla on Zulip.
- Reorders things slightly so that more important things
  are higher up, and incidental things are lower down, which makes
  reading the code easier.

Co-authored-by: Joshua Nelson <github@jyn.dev>

This directive isn't automatically set by compiletest or x.py, but can
be turned on manually for targets that require it.

…k-Simulacrum

Add needs-unwind to tests that depend on panicking

These tests were found by running the test suite on fuchsia which compiles with `panic=abort` by default, then picking through the failures manually to locate the tests that require unwinding support.

Most of these tests are already opted-out on platforms that compile with `panic=abort` by default. This just generalizes it a bit more so that fuchsia tests can be run properly. Currently, the `needs-unwind` directive needs to be manually passed to compiletest (e.g. via `--test-args '--target-panic=abort'`). Eventually, I would like `x.py` or compiletest to determine whether the directive should be used automatically based on the target panic settings.

Make IdFunctor::try_map_id panic-safe

Addresses FIXME comment created in rust-lang#78313

r? ``@lcnr``

…y, r=lcnr

Improve the readability of `List<T>`.

This commit does the following.
- Expands on some of the things already mentioned in comments.
- Describes the uniqueness assumption, which is critical but wasn't
  mentioned at all.
- Rewrites `empty()` into a clearer form, as provided by Daniel
  Henry-Mantilla on Zulip.
- Reorders things slightly so that more important things
  are higher up, and incidental things are lower down, which makes
  reading the code easier.

r? ``@lcnr``

rustdoc: Show type layout for type aliases

Fixes rust-lang#91265.

At first, you might think, "Why not just click through to the aliased
type?" But, if a type alias instantiates all of the generic parameters
of the aliased type, then it can show layout info even though the
aliased type cannot (because we can't compute layout for generic types).
So, I think it's useful to show layout info for type aliases.

This is a followup of 78d4b453ad2e19d44011b26fc55c949bff5dba3d
(originally part of rust-lang#83501).

Add deprecation warning for --passes

Issue rust-lang#91713 mentored by ``@jyn514``

…gisa

give more help in the unaligned_references lint

Cc rust-lang#82523 (comment) `@kaisq`