previously, we only held a lock for printing the backtrace itself. since all threads were printing to the same file descriptor, that meant random output in the default panic hook would be interleaved with the backtrace. now, we hold the lock for the full duration of the hook, and the output is ordered.

…matthewjasper

Fix regression in the MIR lowering of or-patterns

In rust-lang#126553 I made a silly indexing mistake and regressed the MIR lowering of or-patterns. This fixes it.

r? `@compiler-errors` because I'd like this to be merged quickly 🙏

…dtolnay

impl FusedIterator and a size hint for the error sources iter

cc tracking issue rust-lang#58520

Automatically taint when reporting errors from ItemCtxt

This isn't very robust yet, as you need to use `itemctxt.dcx()` instead of `tcx.dcx()` for it to take effect, but it's at least more convenient than sprinkling `set_tainted_by_errors` calls in individual places.

based on rust-lang#127357

r? `@fmease`

Use verbose style when suggesting changing `const` with `let`

…workingjubilee

fix interleaved output in the default panic hook when multiple threads panic simultaneously

previously, we only held a lock for printing the backtrace itself. since all threads were printing to the same file descriptor, that meant random output in the default panic hook from one thread would be interleaved with the backtrace from another. now, we hold the lock for the full duration of the hook, and the output is ordered.

---

i noticed some odd things while working on this you may or may not already be aware of.

- libbacktrace is included as a submodule instead of a normal rustc crate, and as a result uses `cfg(backtrace_in_std)` instead of a more normal `cfg(feature = "rustc-dep-of-std")`. probably this is left over from before rust used a cargo-based build system?
- the default panic handler uses `trace_unsynchronized`, etc, in `sys::backtrace::print`. as a result, the lock only applies to concurrent *panic handlers*, not concurrent *threads*.  in other words, if another, non-panicking, thread tried to print a backtrace at the same time as the panic handler, we may have UB, especially on windows.
    - we have the option of changing backtrace to enable locking when `backtrace_in_std` is set so we can reuse their lock instead of trying to add our own.

…e-doc, r=fmease

`#[doc(alias)]`'s doc: say that ASCII spaces are allowed

PR rust-lang#77570 allowed ASCII spaces in doc aliases, but the documentation wasn't updated to say so.

The code checking the aliases:
https://github.com/rust-lang/rust/blob/7fdefb804ec300fb605039522a7c0dfc9e7dc366/compiler/rustc_passes/src/check_attr.rs#L693-L704

`@rustbot` label +A-docs

…=Nadrieril

Update `f16`/`f128` FIXMEs that needed `(NEG_)INFINITY`

Just a small fix to the pattern matching tests now that we can. Also contains a small unrelated comment tweak.

…-errors

small search graph refactor

small improvements which shouldn't impact behavior.

r? `@compiler-errors`