Rollup of 8 pull requests Successful merges: - #66498 (Remove unused feature gates) - #68816 (Tweak borrow error on `FnMut` when `Fn` is expected) - #68824 (Enable Control Flow Guard in rustbuild) - #69022 (traits: preallocate 2 Vecs of known initial size) - #69031 (Use `dyn Trait` more in tests) - #69044 (Don't run coherence twice for future-compat lints) - #69047 (Don't rustfmt check the vendor directory.) - #69055 (Clean up E0307 explanation) Failed merges: r? @ghost
For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc guide.