…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`

…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

…eworking, r=lcnr

More trait error reworking

More work on rust-lang#127492, specifically those sub-bullets under "Move trait error reporting to `error_reporting::traits`". Stacked on top of rust-lang#127493.

This does introduce new `TypeErrCtxt.*Ext` traits, but those will be deleted soon. Splitting this work into bite-sized pieces is the only way that it's gonna be feasible to both author and review ❤️

r? lcnr

…=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``