Use ptr::drop_in_place for VecDeque::truncate and VecDeque::clear
This commit allows `VecDeque::truncate` to take advantage of its (largely) contiguous memory layout and is consistent with the change in #64432 for `Vec`. As with the change to `Vec::truncate`, this changes both:
- the drop order, from back-to-front to front-to-back
- the behavior when dropping an element panics
For consistency, it also changes the behavior when dropping an element panics for `VecDeque::clear`.
These changes in behavior can be observed. This example ([playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=d0b1f2edc123437a2f704cbe8d93d828))
```rust
use std::collections::VecDeque;
fn main() {
struct Bomb(usize);
impl Drop for Bomb {
fn drop(&mut self) {
panic!(format!("{}", self.0));
}
}
let mut v = VecDeque::from(vec![Bomb(0), Bomb(1)]);
std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
v.truncate(0);
}));
std::mem::forget(v);
}
```
panics printing `1` today and succeeds. `v.clear()` panics printing `0` today and succeeds. With the change, `v.clear()`, `v.truncate(0)`, and dropping the `VecDeque` all panic printing `0` first and then abort with a double-panic printing `1`.
The motivation for this was making `VecDeque::truncate` more efficient since it was used in the implementation of `VecDeque::clone_from` (#65069), but it also makes behavior more consistent within the `VecDeque` and with `Vec` if that change is accepted (this probably doesn't make sense to merge if not).
This might need a crater run and an FCP as well.
Fixed PhantomData markers in Arc and Rc
Include owned internal structs in `PhantomData` markers in `Arc` (`PhantomData<T>` => `PhantomData<ArcInner<T>>`) and `Rc` (`PhantomData<T>` => `PhantomData<RcBox<T>>`).
improve from_raw_parts docs
Triggered by https://github.com/rust-lang/rfcs/pull/2806. Hopefully this helps clarify that joining slices across allocations is not possible in Rust currently.
r? @Centril
doc(str): show example of chars().count() under len()
the docs are great at explaining that .len() isn't like in other
languages but stops short of explaining how to get the character length.
the docs are great at explaining that .len() isn't like in other
languages but stops short of explaining how to get the character length.
r? @steveklabnik
Implement ordered/sorted iterators on BinaryHeap as per #59278
I've implemented the ordered version of iterator on BinaryHeap as per #59278.
# Added methods:
* `.into_iter_sorted()`
* like `.into_iter()`; but returns elements in heap order
* `.drain_sorted()`
* like `.drain()`; but returns elements in heap order
* It's a bit _lazy_; elements are removed on drop. (Edit: it’s similar to vec::Drain)
For `DrainSorted` struct, I implemented `Drop` trait following @scottmcm 's [suggestion](https://github.com/rust-lang/rust/issues/59278#issuecomment-537306925)
# ~TODO~ DONE
* ~I think I need to add more tests other than doctest.~
# **Notes:**
* we renamed `_ordered` to `_sorted`, because the latter is more common in rust libs. (as suggested by @KodrAus )
Stabilize `Option::flatten`
- PR: https://github.com/rust-lang/rust/pull/60256
- Tracking issue: https://github.com/rust-lang/rust/issues/60258
@elahn
> I was trying to `flat_map()` and found `map().flatten()` does the trick. This has been on nightly for 4 months, can we stabilise it?
@ethanboxx
> @Centril Helped me get this merged. What is the stabilization process?
@Centril
> @ethanboxx I'd just file a PR to stabilize it and we'll ask T-libs to FCP.
So here I am.
I am was unsure what number to put in `since = "-"` so I copied what someone had done in a recent PR.
Rc: value -> allocation
See https://github.com/rust-lang/rust/issues/64484. This does not yet edit `Arc` as I first wanted to be sure we agree on the terminology the way it actually ends up. "value" as a term appears a lot in this file, and sometimes it refers to the value stored inside the `RcBox` while sometimes it refers to the `RcBox` itself. I tried to properly tease these apart but may have made some mistakes. The former should now always be called "inner value" and the latter "allocation".
One area where I was very unsure of which terminology is dropping: the `value` field of the `RcBox` will get dropped *earlier* than the `RcBox` itself if there are weak references. I decided that "dropping the value stored in the allocation" refers to dropping the value field, while "destroying the allocation" refers to actually freeing its backing memory.
r? @Centril
BTreeSet symmetric_difference & union optimized
No scalability changes, but:
- Grew the cmp_opt function (shared by symmetric_difference & union) into a MergeIter, with less memory overhead than the pairs of Peekable iterators now, speeding up ~20% on my machine (not so clear on Travis though, I actually switched it off there because it wasn't consistent about identical code). Mainly meant to improve readability by sharing code, though it does end up using more lines of code. Extending and reusing the MergeIter in btree_map might be better, but I'm not sure that's possible or desirable. This MergeIter probably pretends to be more generic than it is, yet doesn't declare to be an iterator because there's no need to, it's only there to help construct genuine iterators SymmetricDifference & Union.
- Compact the code of #64820 by moving if/else into match guards.
r? @bluss
- Compatible with Emscripten 1.38.46-upstream or later upstream.
- Refactors the Emscripten target spec to share code with other wasm
targets.
- Replaces the old incorrect wasm32 C call ABI with the correct one,
preserving the old one as wasm32_bindgen_compat for wasm-bindgen
compatibility.
- Updates the varargs ABI used by Emscripten and deletes the old one.
- Removes the obsolete wasm32-experimental-emscripten target.
- Uses EMCC_CFLAGS on CI to avoid the timeout problems with #63649.
std::fmt: reorder docs
This moves the "Formatting Parameters" section up above right after the discussion of named and positional arguments. Then comes the "Syntax" section, summarizing the discussion of format string syntax.
And only *then* we get to "Formatting Traits" -- that section has some *huge* code examples, so it really should not interrupt the discussion of the grammar. Also users are much more likely to come here to learn about the format string grammar than to come here to learn about the `Binary` trait.
Split non-CAS atomic support off into target_has_atomic_load_store
This PR implements my proposed changes in https://github.com/rust-lang/rust/issues/32976#issuecomment-518542029 by removing `target_has_atomic = "cas"` and splitting `target_has_atomic` into two separate `cfg`s:
* `target_has_atomic = 8/16/32/64/128`: This indicates the largest width that the target can atomically CAS (which implies support for all atomic operations).
* ` target_has_atomic_load_store = 8/16/32/64/128`: This indicates the largest width that the target can support loading or storing atomically (but may not support CAS).
cc #32976
r? @alexcrichton
