Adds notes pointing at the non-nullary variants, and uses "custom
discriminant" language to be consistent with the Reference.

…ect_lifetime_defaults_map

…d_lang_items, missing_lang_items, postorder_cnums and maybe_unused_extern_crates

…erister

Use arenas to avoid Lrc in queries rust-lang#2

The `Remove subtle Default impl for Value` makes the compilation stop due earlier due to cycle errors, since there's no longer a default value to continue the compilation with.

Based on rust-lang#59540.

…avis

Suggest dereferencing on assignment to mutable borrow

Fix rust-lang#33570

…=estebank

tweak discriminant on non-nullary enum diagnostic

Adds notes pointing at the non-nullary variants, and uses "custom
discriminant" language to be consistent with the Reference.

Fixes rust-lang#61039.

r? @estebank

fix dangling reference in Vec::append

Turns out I forgot to enable Miri again for the Vec tests. And there was a dangling reference hiding in there!  `get_unchecked_mut` is UB to call on an empty vector (there is no memory to get a reference to), and yet this code did it.

Box::into_unique: do the reborrow-to-raw *after* destroying the Box

Currently we first "reborrow" the box to a raw pointer, and then `forget` it. When tracking raw pointers more strictly (something I am experimenting with locally in Miri), the "use" induced by passing the box to `forget` invalidates the previously created raw pointer.

So adjust my hack from rust-lang#58429 to reorder the two operations.

…oop, r=estebank

Fix overflowing literal lint in loops

Fixes rust-lang#60459.

r? @estebank