Stop BTreeMap casts from reborrowing
Down in btree/node.rs, the interface and use of `cast_unchecked` look a bit shady. It's really just there for inverting `forget_type` which does not borrow. By borrowing we can't write the same `cast_unchecked` in the same way at the Handle level.
No change in undefined behaviour or performance.
Hard way to respect BTreeMap's minimum node length
Resolves#74834 the hard way (though not the hardest imaginable).
Benchmarks (which are all biased/realistic, inserting keys in ascending order) say:
```
benchcmp r0 r1 --threshold 10
name r0 ns/iter r1 ns/iter diff ns/iter diff % speedup
btree::map::clone_slim_100_and_clear 2,183 2,723 540 24.74% x 0.80
btree::map::clone_slim_100_and_drain_all 3,652 4,173 521 14.27% x 0.88
btree::map::clone_slim_100_and_drain_half 3,320 3,940 620 18.67% x 0.84
btree::map::clone_slim_100_and_into_iter 2,154 2,717 563 26.14% x 0.79
btree::map::clone_slim_100_and_pop_all 3,372 3,870 498 14.77% x 0.87
btree::map::clone_slim_100_and_remove_all 5,111 5,647 536 10.49% x 0.91
btree::map::clone_slim_100_and_remove_half 3,259 3,821 562 17.24% x 0.85
btree::map::iter_0 1,733 1,509 -224 -12.93% x 1.15
btree::map::iter_100 2,714 3,739 1,025 37.77% x 0.73
btree::map::iter_10k 3,728 4,269 541 14.51% x 0.87
btree::map::range_unbounded_unbounded 28,426 36,631 8,205 28.86% x 0.78
btree::map::range_unbounded_vs_iter 28,808 34,056 5,248 18.22% x 0.85
```
This difference is not caused by the `debug_assert`-related code in the function `splitpoint`, it's the same without.
The previous `assert_eq` generated quite some code, which is especially
problematic when this call is inlined. This commit also slightly
improves the panic message from:
assertion failed: `(left == right)`
left: `3`,
right: `2`: destination and source slices have different lengths
...to:
source slice length (2) does not match destination slice length (3)
fix wrong word in documentation
Change "two" to "three", since there are three significantly different things printed below that sentence:
---
While these:
```rust
println!("{}, `{name:.*}` has 3 fractional digits", "Hello", 3, name=1234.56);
println!("{}, `{name:.*}` has 3 characters", "Hello", 3, name="1234.56");
println!("{}, `{name:>8.*}` has 3 right-aligned characters", "Hello", 3, name="1234.56");
```
print two significantly different things:
``` rust
Hello, `1234.560` has 3 fractional digits
Hello, `123` has 3 characters
Hello, ` 123` has 3 right-aligned characters
```
---
[`https://doc.rust-lang.org/std/fmt/#precision`](https://doc.rust-lang.org/std/fmt/#precision)
Implement `into_keys` and `into_values` for associative maps
This PR implements `into_keys` and `into_values` for HashMap and BTreeMap types. They are implemented as unstable, under `map_into_keys_values` feature.
Fixes#55214.
r? @dtolnay
Move bulk of BTreeMap::insert method down to new method on handle
Adjust the boundary between the map and node layers for insertion: do more in the node layer, keep root manipulation and pointer dereferencing separate. No change in undefined behaviour or performance.
r? @Mark-Simulacrum
BTreeMap: define forget_type only when relevant
Similar to `forget_node_type` for handles.
No effect on generated code, apart maybe from the superfluous calls that might not have been optimized away.
r? @Mark-Simulacrum
BTreeMap::drain_filter should not touch the root during iteration
Although Miri doesn't point it out, I believe there is undefined behaviour using `drain_filter` when draining the 11th-last element from a tree that was larger. When this happens, the last remaining child nodes are merged, the root becomes empty and is popped from the tree. That last step establishes a mutable reference to the node elected root and writes a pointer in `node::Root`, while iteration continues to visit the same node.
This is mostly code from #74437, slightly adapted.
Stabilize Vec::leak as a method
Closes https://github.com/rust-lang/rust/issues/62195
The signature is changed to a method rather than an associated function:
```diff
-pub fn leak<'a>(vec: Vec<T>) -> &'a mut [T]
+pub fn leak<'a>(self) -> &'a mut [T]
```
The reason for `Box::leak` not to be a method (`Deref` to an arbitrary `T` which might have its own, different `leak` method) does not apply.
add `slice::array_chunks` to std
Now that #74113 has landed, these methods are suddenly usable. A rebirth of #72334
Tests are directly copied from `chunks_exact` and some additional tests for type inference.
r? @withoutboats as you are both part of t-libs and working on const generics. closes#60735
