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Cleanup a `use` in a raw_vec test
`allocator` is deprecated in favor of `alloc`, and `Alloc` is already imported
through `super::*`.
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Add some explanations for #[must_use]
`#[must_use]` can be given a string argument which is shown whilst warning for things.
We should add a string argument to most of the user-exposed ones.
I added these for everything but the operators, mostly because I'm not sure what to write there or if we need anything there.
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Make `String::new()` const
Following the steps of https://github.com/rust-lang/rust/pull/50233 , make `String::new()` a `const fn`.
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Also remove some unnecessary debug_assert! when creating the shared
root, since the root should be stored in the rodata and thus be
impossible to accidentally modify.
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Rename Pin to PinMut, and some more breaking changes
As discussed at [1] §3 and [2] and [3], a formal look at pinning requires considering a distinguished "shared pinned" mode/typestate. Given that, it seems desirable to at least eventually actually expose that typestate as a reference type. This renames Pin to PinMut, freeing the name Pin in case we want to use it for a shared pinned reference later on.
[1] https://www.ralfj.de/blog/2018/04/10/safe-intrusive-collections-with-pinning.html
[2] https://github.com/rust-lang/rfcs/pull/2349#issuecomment-379250361
[3] https://github.com/rust-lang/rust/issues/49150#issuecomment-380488275
Cc @withoutboats
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`allocator` is deprecated in favor of `alloc`, and `Alloc` is already imported
through `super::*`.
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This splits into_slices() into into_key_slice() and into_val_slice(). While the
extra calls would get optimized out, this is a useful semantic change since we
call keys() while iterating, and we don't want to construct and out-of-bounds
val() pointer in the process if we happen to be pointing to the shared static
root.
This also paves the way for doing the alignment handling conditional differently
for the keys and values.
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We modify the drop implementation in IntoIter to not drop the shared root
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This gives a pointer to that static empty node instead of allocating
a new node, and then whenever inserting makes sure that the root
isn't that empty node.
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This way we can safely statically allocate a LeafNode to use as the
placeholder before allocating, and any type accessing it will be able to
access the metadata at the same offset.
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As discussed at [1] §3 and [2] and [3], a formal look at pinning requires considering a
distinguished "shared pinned" mode/typestate. Given that, it seems desirable to
at least eventually actually expose that typestate as a reference type. This
renames Pin to PinMut, freeing the name Pin in case we want to use it for a
shared pinned reference later on.
[1] https://www.ralfj.de/blog/2018/04/10/safe-intrusive-collections-with-pinning.html
[2] https://github.com/rust-lang/rfcs/pull/2349#issuecomment-379250361
[3] https://github.com/rust-lang/rust/issues/49150#issuecomment-380488275
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The Option is always Some until drop, where it becomes None. Make
this more explicit and avoid unwraps by using ManuallyDrop.
This change should be performance-neutral as LLVM already optimizes
the unwraps away in the inlined code.
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Introduce RangeInclusive::{new, start, end} methods and make the fields private.
cc #49022
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stabilize `#[must_use]` for functions and must-use comparison operators (RFC 1940)
r? @nikomatsakis
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Make `Vec::new` a `const fn`
`RawVec::empty/_in` are a hack. They're there because `if size_of::<T> == 0 { !0 } else { 0 }` is not allowed in `const` yet. However, because `RawVec` is unstable, the `empty/empty_in` constructors can be removed when #49146 is done...
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Added new()/start()/end() methods to RangeInclusive.
Changed the lowering of `..=` to use RangeInclusive::new().
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m*n lines of implementation deserves m*n lines of tests
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GitHub users: I think you can add ?w=1 to the url
for a vastly cleaner whitespace-ignoring diff
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This is in the matter of RFC 1940 and tracking issue #43302.
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std: Mark `ptr::Unique` with `#[doc(hidden)]`
`Unique` is now perma-unstable, so let's hide its docs.
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Partial future-proofing for Box<T, A>
In some ways, this is similar to @eddyb's PR #47043 that went stale, but doesn't cover everything. Notably, this still leaves Box internalized as a pointer in places, so practically speaking, only ZSTs can be practically added to the Box type with the changes here (the compiler ICEs otherwise).
The Box type is not changed here, that's left for the future because I want to test that further first, but this puts things in place in a way that hopefully will make things easier.
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Added missing `.` in docs.
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mark std::str::replace(,n) as #[must_use]
let x = "a b c c";
x.replacen("c", "d", 2");
might not do what people might think it does.
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As of now, Box only contains a Unique pointer, so this is the sole
argument to box_free. Consequently, we remove the code supporting
the previous box_free signature. We however keep the old definition
for bootstrapping purpose.
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Add repeat method on slice
Fixes #48784.
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Add inherent methods in libcore for [T], [u8], str, f32, and f64
# Background
Primitive types are defined by the language, they don’t have a type definition like `pub struct Foo { … }` in any crate. So they don’t “belong” to any crate as far as `impl` coherence is concerned, and on principle no crate would be able to define inherent methods for them, without a trait. Since we want these types to have inherent methods anyway, the standard library (with cooperation from the compiler) bends this rule with code like [`#[lang = "u8"] impl u8 { /*…*/ }`](https://github.com/rust-lang/rust/blob/1.25.0/src/libcore/num/mod.rs#L2244-L2245). The `#[lang]` attribute is permanently-unstable and never intended to be used outside of the standard library.
Each lang item can only be defined once. Before this PR there is one impl-coherence-rule-bending lang item per primitive type (plus one for `[u8]`, which overlaps with `[T]`). And so one `impl` block each. These blocks for `str`, `[T]` and `[u8]` are in liballoc rather than libcore because *some* of the methods (like `<[T]>::to_vec(&self) -> Vec<T> where T: Clone`) need a global memory allocator which we don’t want to make a requirement in libcore. Similarly, `impl f32` and `impl f64` are in libstd because some of the methods are based on FFI calls to C’s `libm` and we want, as much as possible, libcore not to require “runtime support”.
In libcore, the methods of `str` and `[T]` that don’t allocate are made available through two **unstable traits** `StrExt` and `SliceExt` (so the traits can’t be *named* by programs on the Stable release channel) that have **stable methods** and are re-exported in the libcore prelude (so that programs on Stable can *call* these methods anyway). Non-allocating `[u8]` methods are not available in libcore: https://github.com/rust-lang/rust/issues/45803. Some `f32` and `f64` methods are in an unstable `core::num::Float` trait with stable methods, but that one is **not in the libcore prelude**. (So as far as Stable programs are concerns it doesn’t exist, and I don’t know what the point was to mark these methods `#[stable]`.)
https://github.com/rust-lang/rust/issues/32110 is the tracking issue for these unstable traits.
# High-level proposal
Since the standard library is already bending the rules, why not bend them *a little more*? By defining a few additional lang items, the compiler can allow the standard library to have *two* `impl` blocks (in different crates) for some primitive types.
The `StrExt` and `SliceExt` traits still exist for now so that we can bootstrap from a previous-version compiler that doesn’t have these lang items yet, but they can be removed in next release cycle. (`Float` is used internally and needs to be public for libcore unit tests, but was already `#[doc(hidden)]`.) I don’t know if https://github.com/rust-lang/rust/issues/32110 should be closed by this PR, or only when the traits are entirely removed after we make a new bootstrap compiler.
# Float methods
Among the methods of the `core::num::Float` trait, three are based on LLVM intrinsics: `abs`, `signum`, and `powi`. PR https://github.com/rust-lang/rust/pull/27823 “Remove dependencies on libm functions from libcore” moved a bunch of `core::num::Float` methods back to libstd, but left these three behind. However they aren’t specifically discussed in the PR thread. The `compiler_builtins` crate defines `__powisf2` and `__powidf2` functions that look like implementations of `powi`, but I couldn’t find a connection with the `llvm.powi.f32` and `llvm.powi.f32` intrinsics by grepping through LLVM’s code.
In discussion starting at https://github.com/rust-lang/rust/issues/32110#issuecomment-370647922 Alex says that we do not want methods in libcore that require “runtime support”, but it’s not clear whether that applies to these `abs`, `signum`, or `powi`. In doubt, I’ve **removed** them for the trait and moved them to inherent methods in libstd for now. We can move them back later (or in this PR) if we decide that’s appropriate.
# Change details
For users on the Stable release channel:
* I believe this PR does not make any breaking change
* Some methods for `[u8]`, `f32`, and `f64` are newly available to `#![no_std]` users (fixes https://github.com/rust-lang/rust/issues/45803)
* There should be no visible change for `std` users in terms of what programs compile or what their behavior is. (Only in compiler error messages, possibly.)
For Nightly users, additionally:
* The unstable `StrExt` and `SliceExt` traits are gone
* Their methods are now inherent methods of `str` and `[T]` (so only code that explicitly named the traits should be affected, not "normal" method calls)
* The `abs`, `signum` and `powi` methods of the `Float` trait are gone
* The `Float` trait’s unstable feature name changed to `float_internals` with no associated tracking issue, to reflect it being a permanently unstable implementation detail rather than a public API on a path to stabilization.
* Its remaining methods are now inherent methods of `f32` and `f64`.
-----
CC @rust-lang/libs for the API changes, @rust-lang/compiler for the new lang items
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smaller PR just to fix #50002
I pulled this out of #50010 to make it easier to backport to beta if necessary, considering that inclusive range syntax is stabilizing soon (?).
It fixes a bug in `<str>::index_mut` with `(..=end)` ranges (#50002), which prior to this fix was not only unusable but also UB in the cases where it "worked" (it gave improperly truncated UTF-8).
(not that I can imagine why anybody would *use* `<str>::index_mut`... but I'm not here to judge)
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`Float` still needs to be public for libcore unit tests.
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… previously in the unstable core::num::Float trait.
Per https://github.com/rust-lang/rust/issues/32110#issuecomment-379503183,
the `abs`, `signum`, and `powi` methods are *not* included for now
since they rely on LLVM intrinsics and we haven’t determined yet whether
those instrinsics lower to calls to libm functions on any platform.
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