The reference automatically coerces to a pointer. Writing an explicit
cast here is slightly misleading because that's most commonly used when
a pointer needs to be converted from one pointer type to another, e.g.
`*const c_void` to `*const sigaction` or vice versa.

…ding

This decomposes an error message in generic constants into more specific branches, for better
readability.

When `cargo report future-incompatibilities` is stabilized
(see rust-lang#71249), this will cause dependencies that trigger
this lint to be included in the report.

Use `libc::sigaction()` instead of `sys::signal()` to prevent a deadlock

Fixes rust-lang#88585. POSIX [specifies](https://man7.org/linux/man-pages/man3/fork.3p.html) that after forking,
> to avoid errors, the child process may only execute async-signal-safe operations until such time as one of the exec functions is called.

Rust's standard library does not currently adhere to this, as evidenced by rust-lang#88585. The child process calls [`sys::signal()`](https://github.com/rust-lang/rust/blob/7bf0736e130e2203c58654f7353dbf9575e49d5c/library/std/src/sys/unix/android.rs#L76), which on Android calls [`libc::dlsym()`](https://github.com/rust-lang/rust/blob/7bf0736e130e2203c58654f7353dbf9575e49d5c/library/std/src/sys/unix/weak.rs#L101), which is [**not**](https://man7.org/linux/man-pages/man7/signal-safety.7.html) async-signal-safe, and in fact causes a deadlock in the example in rust-lang#88585.

I think the easiest solution here would be to just call `libc::sigaction()` instead, which [is](https://man7.org/linux/man-pages/man7/signal-safety.7.html) async-signal-safe, provides the functionality we need, and is apparently available on all Android versions because it is also used e.g. [here](https://github.com/rust-lang/rust/blob/7bf0736e130e2203c58654f7353dbf9575e49d5c/library/std/src/sys/unix/stack_overflow.rs#L112-L114).

Move generic error message to separate branches

This decomposes an error message in generic constants into more specific branches, for better
readability.

r? `@lcnr`

…, r=estebank

Add check for duplicated doc aliases

r? `@estebank`

…lett

Fix Lower/UpperExp formatting for integers and precision zero

Fixes the integer part of rust-lang#89493 (I daren't touch the floating-point formatting code). The issue is that the "subtracted" precision essentially behaves like extra trailing zeros, but this is not currently reflected in the code properly.

…esleywiser

Make `proc_macro_derive_resolution_fallback` a future-breakage lint

When `cargo report future-incompatibilities` is stabilized
(see rust-lang#71249), this will cause dependencies that trigger
this lint to be included in the report.

…um, r=oli-obk,tmiasko

Document behavior of  `MaybeLiveLocals` regarding enums and field-senstivity

This arose from a [discussion on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/189540-t-compiler.2Fwg-mir-opt/topic/MaybeLiveLocals.20and.20Discriminants) where a new contributor attempted to implement a dead-store elimination pass using this analysis. They ran into a nasty hack around `SetDiscriminant` the effect of which is to lets handle assignments of literals to enum-typed locals (e.g. `x = Some(4)`) correctly. This took me a while to figure out.

Document this oddity, so the next person will have an easier time, and add a test to enshrine the current behavior.

r? `@tmiasko`

…r=petrochenkov

Make an initial guess for metadata size to reduce buffer resizes

When reading metadata, the compiler starts with a `Vec::new()`, which will need to grow repeatedly as the metadata gets decompressed into it. Reduce the number of resizes by starting out at the size of the compressed data.