BTreeMap: move up reference to map's root from NodeRef
Since the introduction of `NodeRef` years ago, it also contained a mutable reference to the owner of the root node of the tree (somewhat disguised as *const). Its intent is to be used only when the rest of the `NodeRef` is no longer needed. Moving this to where it's actually used, thought me 2 things:
- Some sort of "postponed mutable reference" is required in most places that it is/was used, and that's exactly where we also need to store a reference to the length (number of elements) of the tree, for the same reason. The length reference can be a normal reference, because the tree code does not care about tree length (just length per node).
- It's downright obfuscation in `from_sorted_iter` (transplanted to #75329)
- It's one of the reasons for the scary notice on `reborrow_mut`, the other one being addressed in #73971.
This does repeat the raw pointer code in a few places, but it could be bundled up with the length reference.
r? `@Mark-Simulacrum`
This avoids overlapping a reference covering the data field,
which may be changed due in concurrent conditions. This fully
fixed the UB mainfested with `new_cyclic`.
Since trait implementations cannot be unstable, we should only add them
when the as_str feature gets stabilized. Until then, only `.as_str()` is
available (behind a feature gate).
Move various ui const tests to `library`
Move:
- `src\test\ui\consts\const-nonzero.rs` to `library\core`
- `src\test\ui\consts\ascii.rs` to `library\core`
- `src\test\ui\consts\cow-is-borrowed` to `library\alloc`
Part of #76268
r? @matklad
Move some Vec UI tests into alloc unit tests
A bit of work towards #76268, makes a number of the Vec UI tests that are simply running code into unit tests. Ensured that they are being run when testing liballoc locally.
rename MaybeUninit slice methods
The `first` methods conceptually point to the whole slice, not just its first element, so rename them to be consistent with the raw ptr methods on ref-slices.
Also, do the equivalent of https://github.com/rust-lang/rust/pull/76047 for the slice reference getters, and make them part of https://github.com/rust-lang/rust/issues/63569 (so far they somehow had no tracking issue).
* first_ptr -> slice_as_ptr
* first_ptr_mut -> slice_as_mut_ptr
* slice_get_ref -> slice_assume_init_ref
* slice_get_mut -> slice_assume_init_mut
BTreeMap: introduce marker::ValMut and reserve Mut for unique access
The mutable BTreeMap iterators (apart from `DrainFilter`) are double-ended, meaning they have to rely on a front and a back handle that each represent a reference into the tree. Reserve a type category `marker::ValMut` for them, so that we guarantee that they cannot reach operations on handles with borrow type `marker::Mut`and that these operations can assume unique access to the tree.
Including #75195, benchmarks report no genuine change:
```
benchcmp old new --threshold 5
name old ns/iter new ns/iter diff ns/iter diff % speedup
btree::map::iter_100 3,333 3,023 -310 -9.30% x 1.10
btree::map::range_unbounded_vs_iter 36,624 31,569 -5,055 -13.80% x 1.16
```
r? @Mark-Simulacrum
This is very similar to the existing `Box<[T; N]>: TryFrom<Box<[T]>>`, but allows avoiding the `shrink_to_fit` if you have a vector and not a boxed slice.
Move:
- `src\test\ui\consts\const-nonzero.rs` to `library\core`
- `src\test\ui\consts\ascii.rs` to `library\core`
- `src\test\ui\consts\cow-is-borrowed` to `library\alloc`
Part of #76268
The InPlaceIterable debug assert checks that the write pointer
did not advance beyond the read pointer. But TrustedRandomAccess
never advances the read pointer, thus triggering the assert.
Skip the assert if the source pointer did not change during iteration.
The optimization meant that every extend code path had to emit llvm
IR for from_iter and extend spec_extend, which likely impacts
compile times while only improving a few edge-cases
switch to try_fold and segregate the drop handling to keep
collect::<Vec<u8>>() and similar optimizer-friendly
It comes at the cost of less accurate debug_asserts and code complexity
