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mem::zeroed/uninit: panic on types that do not permit zero-initialization #66059

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merged 10 commits into from
Mar 11, 2020

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RalfJung
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@RalfJung RalfJung commented Nov 3, 2019

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 3, 2019
src/librustc_index/vec.rs Outdated Show resolved Hide resolved
@RalfJung
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RalfJung commented Nov 3, 2019

@pietroalbini how strapped are we on crater resources these days? This PR has the potential to "break" unsafe code that causes UB but got away with it so far. We have linted against some instances of this (on stable for 1 cycle now) but the static check has false negatives, of course, and probably not all affected code got updated. So, it would be good to get a full crater run (with tests) to estimate the fallout.

(Also, looks like CI failed but the but didn't post anything?)

@Mark-Simulacrum
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Crater queue is pretty empty so you can probably queue yourself, we're decently okay on resources these days (and I imagine this is good to land at start of cycle, so you're likely waiting ~3 days anyway for beta branching to finish).

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RalfJung commented Nov 3, 2019

lol, the first thing this finds is an illegal zero-inititalization in the compiler itself.^^

2019-11-03T17:34:47.0150572Z thread 'rustc' panicked at 'attempted to zero-initialize non-zero type `[syntax::ptr::P<syntax::ast::Item>; 1]`', /checkout/src/libcore/mem/mod.rs:493:5
2019-11-03T17:34:47.0150653Z note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

@Mark-Simulacrum Great! I don't have crater powers, but I'll let you know when we have something worth testing. And indeed this should land after beta branching; I expected review + bors queuing to take that long anyway.

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RalfJung commented Nov 3, 2019

The backtrace points to smallvec:

  17: core::mem::uninitialized
             at ./src/libcore/mem/mod.rs:493
  18: smallvec::SmallVec<A>::new
             at /home/r/.cargo/registry/src/github.com-1ecc6299db9ec823/smallvec-0.6.10/lib.rs:410
  19: syntax_expand::expand::MacroExpander::expand_crate
             at src/libsyntax_expand/expand.rs:311

This is thus likely already fixed upstream by servo/rust-smallvec#162.

@mbrubeck @emilio any chance of a patch release with the fix? This is blocking landing better checks for incorrect uses of uninitialized memory, as right now rustc itself violates those checks.

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emilio commented Nov 3, 2019

Yup! Just published smallvec which contains servo/rust-smallvec#175 :)

@RalfJung
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RalfJung commented Nov 3, 2019

Wow, 1.0. :)

But that's a major bump, which we should likely do in a separate PR first.

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RalfJung commented Nov 4, 2019

For now I exempted arrays from the check; given that smallvec 1.0 was only just released, it's probably too early to break users of the 0.6 series. (I also hope we can get a patch release out so users don't need to make a major version bump.)

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RalfJung commented Nov 5, 2019

All right, let's prepare for a crater run

@bors try

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bors commented Nov 5, 2019

⌛ Trying commit 321f9e2 with merge 8045dc6...

bors added a commit that referenced this pull request Nov 5, 2019
mem::zeroed/uninit: panic on types that do not permit zero-initialization

r? @eddyb @oli-obk

Cc #62825
@Centril Centril added needs-fcp This change is insta-stable, so needs a completed FCP to proceed. T-lang Relevant to the language team, which will review and decide on the PR/issue. relnotes Marks issues that should be documented in the release notes of the next release. labels Nov 6, 2019
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RalfJung commented Nov 6, 2019

Need another try build due to the stricter mem::uninitialized checks.

@bors try

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bors commented Nov 6, 2019

⌛ Trying commit f8c69b0 with merge 7469e97dd62119e27ee51feeb04cfdb202e66b2a...

@bors bors added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Mar 11, 2020
@bors bors merged commit a7c2eef into rust-lang:master Mar 11, 2020
@RalfJung RalfJung deleted the panic-on-non-zero branch March 11, 2020 12:51
Centril added a commit to Centril/rust that referenced this pull request Mar 17, 2020
implement zeroed and uninitialized with MaybeUninit

This is the second attempt of doing such a change (first PR: rust-lang#62150). The last change [got reverted](rust-lang#63343) because it [caused](rust-lang#62825) some [issues](rust-lang#52898 (comment)) in [code that incorrectly used these functions](AltF02/x11-rs#99).

Since then, the [problematic code has been fixed](AltF02/x11-rs#101), and rustc [gained a lint](rust-lang#63346) that is able to detect many misuses of these functions statically and a [dynamic check that panics](rust-lang#66059) instead of causing UB for some incorrect uses.

Fixes rust-lang#62825
Centril added a commit to Centril/rust that referenced this pull request Mar 17, 2020
implement zeroed and uninitialized with MaybeUninit

This is the second attempt of doing such a change (first PR: rust-lang#62150). The last change [got reverted](rust-lang#63343) because it [caused](rust-lang#62825) some [issues](rust-lang#52898 (comment)) in [code that incorrectly used these functions](AltF02/x11-rs#99).

Since then, the [problematic code has been fixed](AltF02/x11-rs#101), and rustc [gained a lint](rust-lang#63346) that is able to detect many misuses of these functions statically and a [dynamic check that panics](rust-lang#66059) instead of causing UB for some incorrect uses.

Fixes rust-lang#62825
Centril added a commit to Centril/rust that referenced this pull request Mar 17, 2020
implement zeroed and uninitialized with MaybeUninit

This is the second attempt of doing such a change (first PR: rust-lang#62150). The last change [got reverted](rust-lang#63343) because it [caused](rust-lang#62825) some [issues](rust-lang#52898 (comment)) in [code that incorrectly used these functions](AltF02/x11-rs#99).

Since then, the [problematic code has been fixed](AltF02/x11-rs#101), and rustc [gained a lint](rust-lang#63346) that is able to detect many misuses of these functions statically and a [dynamic check that panics](rust-lang#66059) instead of causing UB for some incorrect uses.

Fixes rust-lang#62825
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Jun 8, 2020
Pkgsrc changes:
 * Remove a couple diffs which are now integrated upstream.
 * Adjust cargo checksums after upstream upgrades.
 * Belatedly bump the curl dependency
 * Unset DESTDIR during the build phase, to work around a mysterious
   build bug deep in the bowels of llvm.
 * Bump nearly all bootstraps to 1.43.1.

Upstream changes:

Version 1.44.0 (2020-06-04)
==========================

Language
--------
- [You can now use `async/.await` with `#[no_std]` enabled.][69033]
- [Added the `unused_braces` lint.][70081]

**Syntax-only changes**

- [Expansion-driven outline module parsing][69838]
```rust
#[cfg(FALSE)]
mod foo {
    mod bar {
        mod baz; // `foo/bar/baz.rs` doesn't exist, but no error!
    }
}
```

These are still rejected semantically, so you will likely receive an error but
these changes can be seen and parsed by macros and conditional compilation.

Compiler
--------
- [Rustc now respects the `-C codegen-units` flag in incremental mode.][70156]
  Additionally when in incremental mode rustc defaults to 256 codegen units.
- [Refactored `catch_unwind`, to have zero-cost unless unwinding is enabled and
  a panic is thrown.][67502]
- [Added tier 3\* support for the `aarch64-unknown-none` and
  `aarch64-unknown-none-softfloat` targets.][68334]
- [Added tier 3 support for `arm64-apple-tvos` and
  `x86_64-apple-tvos` targets.][68191]

Libraries
---------
- [Special cased `vec![]` to map directly to `Vec::new()`.][70632] This allows
  `vec![]` to be able to be used in `const` contexts.
- [`convert::Infallible` now implements `Hash`.][70281]
- [`OsString` now implements `DerefMut` and `IndexMut` returning
  a `&mut OsStr`.][70048]
- [Unicode 13 is now supported.][69929]
- [`String` now implements `From<&mut str>`.][69661]
- [`IoSlice` now implements `Copy`.][69403]
- [`Vec<T>` now implements `From<[T; N]>`.][68692] Where `N` is less than 32.
- [`proc_macro::LexError` now implements `fmt::Display` and `Error`.][68899]
- [`from_le_bytes`, `to_le_bytes`, `from_be_bytes`, `to_be_bytes`,
  `from_ne_bytes`, and `to_ne_bytes` methods are now `const` for all
  integer types.][69373]

Stabilized APIs
---------------
- [`PathBuf::with_capacity`]
- [`PathBuf::capacity`]
- [`PathBuf::clear`]
- [`PathBuf::reserve`]
- [`PathBuf::reserve_exact`]
- [`PathBuf::shrink_to_fit`]
- [`f32::to_int_unchecked`]
- [`f64::to_int_unchecked`]
- [`Layout::align_to`]
- [`Layout::pad_to_align`]
- [`Layout::array`]
- [`Layout::extend`]

Cargo
-----
- [Added the `cargo tree` command which will print a tree graph of
  your dependencies.][cargo/8062] E.g.
  ```
    mdbook v0.3.2 (/Users/src/rust/mdbook)
  +-- ammonia v3.0.0
  |   +-- html5ever v0.24.0
  |   |   +-- log v0.4.8
  |   |   |   +-- cfg-if v0.1.9
  |   |   +-- mac v0.1.1
  |   |   +-- markup5ever v0.9.0
  |   |       +-- log v0.4.8 (*)
  |   |       +-- phf v0.7.24
  |   |       |   +-- phf_shared v0.7.24
  |   |       |       +-- siphasher v0.2.3
  |   |       |       +-- unicase v1.4.2
  |   |       |           [build-dependencies]
  |   |       |           +-- version_check v0.1.5
  ...
  ```
  You can also display dependencies on multiple versions of the same crate with
  `cargo tree -d` (short for `cargo tree --duplicates`).

Misc
----
- [Rustdoc now allows you to specify `--crate-version` to have rustdoc include
  the version in the sidebar.][69494]

Compatibility Notes
-------------------
- [Rustc now correctly generates static libraries on Windows GNU targets with
  the `.a` extension, rather than the previous `.lib`.][70937]
- [Removed the `-C no_integrated_as` flag from rustc.][70345]
- [The `file_name` property in JSON output of macro errors now points the actual
  source file rather than the previous format of `<NAME macros>`.][70969]
  **Note:** this may not point a file that actually exists on the user's system.
- [The minimum required external LLVM version has been bumped to LLVM 8.][71147]
- [`mem::{zeroed, uninitialised}` will now panic when used with types that do
  not allow zero initialization such as `NonZeroU8`.][66059] This was
  previously a warning.
- [In 1.45.0 (the next release) converting a `f64` to `u32` using the `as`
  operator has been defined as a saturating operation.][71269] This was
  previously undefined behaviour, you can use the `{f64, f32}::to_int_unchecked`
  methods to continue using the current behaviour which may desirable in rare
  performance sensitive situations.

Internal Only
-------------
These changes provide no direct user facing benefits, but represent significant
improvements to the internals and overall performance of rustc and
related tools.

- [dep_graph Avoid allocating a set on when the number reads are small.][69778]
- [Replace big JS dict with JSON parsing.][71250]

[69373]: rust-lang/rust#69373
[66059]: rust-lang/rust#66059
[68191]: rust-lang/rust#68191
[68899]: rust-lang/rust#68899
[71147]: rust-lang/rust#71147
[71250]: rust-lang/rust#71250
[70937]: rust-lang/rust#70937
[70969]: rust-lang/rust#70969
[70632]: rust-lang/rust#70632
[70281]: rust-lang/rust#70281
[70345]: rust-lang/rust#70345
[70048]: rust-lang/rust#70048
[70081]: rust-lang/rust#70081
[70156]: rust-lang/rust#70156
[71269]: rust-lang/rust#71269
[69838]: rust-lang/rust#69838
[69929]: rust-lang/rust#69929
[69661]: rust-lang/rust#69661
[69778]: rust-lang/rust#69778
[69494]: rust-lang/rust#69494
[69403]: rust-lang/rust#69403
[69033]: rust-lang/rust#69033
[68692]: rust-lang/rust#68692
[68334]: rust-lang/rust#68334
[67502]: rust-lang/rust#67502
[cargo/8062]: rust-lang/cargo#8062
[`PathBuf::with_capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.with_capacity
[`PathBuf::capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.capacity
[`PathBuf::clear`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.clear
[`PathBuf::reserve`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve
[`PathBuf::reserve_exact`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve_exact
[`PathBuf::shrink_to_fit`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.shrink_to_fit
[`f32::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_int_unchecked
[`f64::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_int_unchecked
[`Layout::align_to`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.align_to
[`Layout::pad_to_align`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.pad_to_align
[`Layout::array`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.array
[`Layout::extend`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.extend
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Jun 9, 2020
Version 1.44.0 (2020-06-04)
==========================

Language
--------
- [You can now use `async/.await` with `#[no_std]` enabled.][69033]
- [Added the `unused_braces` lint.][70081]

**Syntax-only changes**

- [Expansion-driven outline module parsing][69838]
```rust
#[cfg(FALSE)]
mod foo {
    mod bar {
        mod baz; // `foo/bar/baz.rs` doesn't exist, but no error!
    }
}
```

These are still rejected semantically, so you will likely receive an error but
these changes can be seen and parsed by macros and conditional compilation.

Compiler
--------
- [Rustc now respects the `-C codegen-units` flag in incremental mode.][70156]
  Additionally when in incremental mode rustc defaults to 256 codegen units.
- [Refactored `catch_unwind` to have zero-cost, unless unwinding is enabled and
  a panic is thrown.][67502]
- [Added tier 3\* support for the `aarch64-unknown-none` and
  `aarch64-unknown-none-softfloat` targets.][68334]
- [Added tier 3 support for `arm64-apple-tvos` and
  `x86_64-apple-tvos` targets.][68191]


Libraries
---------
- [Special cased `vec![]` to map directly to `Vec::new()`.][70632] This allows
  `vec![]` to be able to be used in `const` contexts.
- [`convert::Infallible` now implements `Hash`.][70281]
- [`OsString` now implements `DerefMut` and `IndexMut` returning
  a `&mut OsStr`.][70048]
- [Unicode 13 is now supported.][69929]
- [`String` now implements `From<&mut str>`.][69661]
- [`IoSlice` now implements `Copy`.][69403]
- [`Vec<T>` now implements `From<[T; N]>`.][68692] Where `N` is at most 32.
- [`proc_macro::LexError` now implements `fmt::Display` and `Error`.][68899]
- [`from_le_bytes`, `to_le_bytes`, `from_be_bytes`, `to_be_bytes`,
  `from_ne_bytes`, and `to_ne_bytes` methods are now `const` for all
  integer types.][69373]

Stabilized APIs
---------------
- [`PathBuf::with_capacity`]
- [`PathBuf::capacity`]
- [`PathBuf::clear`]
- [`PathBuf::reserve`]
- [`PathBuf::reserve_exact`]
- [`PathBuf::shrink_to_fit`]
- [`f32::to_int_unchecked`]
- [`f64::to_int_unchecked`]
- [`Layout::align_to`]
- [`Layout::pad_to_align`]
- [`Layout::array`]
- [`Layout::extend`]

Cargo
-----
- [Added the `cargo tree` command which will print a tree graph of
  your dependencies.][cargo/8062] E.g.
  ```
    mdbook v0.3.2 (/Users/src/rust/mdbook)
  ├── ammonia v3.0.0
  │   ├── html5ever v0.24.0
  │   │   ├── log v0.4.8
  │   │   │   └── cfg-if v0.1.9
  │   │   ├── mac v0.1.1
  │   │   └── markup5ever v0.9.0
  │   │       ├── log v0.4.8 (*)
  │   │       ├── phf v0.7.24
  │   │       │   └── phf_shared v0.7.24
  │   │       │       ├── siphasher v0.2.3
  │   │       │       └── unicase v1.4.2
  │   │       │           [build-dependencies]
  │   │       │           └── version_check v0.1.5
  ...
  ```
  You can also display dependencies on multiple versions of the same crate with
  `cargo tree -d` (short for `cargo tree --duplicates`).

Misc
----
- [Rustdoc now allows you to specify `--crate-version` to have rustdoc include
  the version in the sidebar.][69494]

Compatibility Notes
-------------------
- [Rustc now correctly generates static libraries on Windows GNU targets with
  the `.a` extension, rather than the previous `.lib`.][70937]
- [Removed the `-C no_integrated_as` flag from rustc.][70345]
- [The `file_name` property in JSON output of macro errors now points the actual
  source file rather than the previous format of `<NAME macros>`.][70969]
  **Note:** this may not point to a file that actually exists on the user's system.
- [The minimum required external LLVM version has been bumped to LLVM 8.][71147]
- [`mem::{zeroed, uninitialised}` will now panic when used with types that do
  not allow zero initialization such as `NonZeroU8`.][66059] This was
  previously a warning.
- [In 1.45.0 (the next release) converting a `f64` to `u32` using the `as`
  operator has been defined as a saturating operation.][71269] This was previously
  undefined behaviour, but you can use the `{f64, f32}::to_int_unchecked` methods to
  continue using the current behaviour, which may be desirable in rare performance
  sensitive situations.

Internal Only
-------------
These changes provide no direct user facing benefits, but represent significant
improvements to the internals and overall performance of rustc and
related tools.

- [dep_graph Avoid allocating a set on when the number reads are small.][69778]
- [Replace big JS dict with JSON parsing.][71250]

[69373]: rust-lang/rust#69373
[66059]: rust-lang/rust#66059
[68191]: rust-lang/rust#68191
[68899]: rust-lang/rust#68899
[71147]: rust-lang/rust#71147
[71250]: rust-lang/rust#71250
[70937]: rust-lang/rust#70937
[70969]: rust-lang/rust#70969
[70632]: rust-lang/rust#70632
[70281]: rust-lang/rust#70281
[70345]: rust-lang/rust#70345
[70048]: rust-lang/rust#70048
[70081]: rust-lang/rust#70081
[70156]: rust-lang/rust#70156
[71269]: rust-lang/rust#71269
[69838]: rust-lang/rust#69838
[69929]: rust-lang/rust#69929
[69661]: rust-lang/rust#69661
[69778]: rust-lang/rust#69778
[69494]: rust-lang/rust#69494
[69403]: rust-lang/rust#69403
[69033]: rust-lang/rust#69033
[68692]: rust-lang/rust#68692
[68334]: rust-lang/rust#68334
[67502]: rust-lang/rust#67502
[cargo/8062]: rust-lang/cargo#8062
[`PathBuf::with_capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.with_capacity
[`PathBuf::capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.capacity
[`PathBuf::clear`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.clear
[`PathBuf::reserve`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve
[`PathBuf::reserve_exact`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve_exact
[`PathBuf::shrink_to_fit`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.shrink_to_fit
[`f32::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_int_unchecked
[`f64::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_int_unchecked
[`Layout::align_to`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.align_to
[`Layout::pad_to_align`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.pad_to_align
[`Layout::array`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.array
[`Layout::extend`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.extend
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Jul 6, 2020
Pkgsrc changes:
 * Remove the clutter caused by the cross-compile setup from Makefile
   (Now consigned to my own private cross.mk file.)
 * Remove a couple of patches which are now integrated upstream.
 * Minor adjustments to a couple of other patches.
 * Adjust cargo checksums after upstream upgrades.
 * Belatedly bump the curl dependency
 * If doing a "dist" build, unset DESTDIR during the build phase,
   to work around a mysterious build bug deep in the bowels of llvm,
   causing llvm tools to be installed to a directory unexpecetd by
   the rest of the rust build, ref.
   rust-lang/rust#73132
   A "dist" build is not expected to be followed by an "install".
 * Bump nearly all bootstraps to 1.43.1; NetBSD earmv7hf bootstrap
   bumped to 1.44.0, as that one now finally builds and works.

Upstream changes:

Version 1.44.0 (2020-06-04)
==========================

Language
--------
- [You can now use `async/.await` with `#[no_std]` enabled.][69033]
- [Added the `unused_braces` lint.][70081]

**Syntax-only changes**

- [Expansion-driven outline module parsing][69838]
```rust
#[cfg(FALSE)]
mod foo {
    mod bar {
        mod baz; // `foo/bar/baz.rs` doesn't exist, but no error!
    }
}
```

These are still rejected semantically, so you will likely receive an error but
these changes can be seen and parsed by macros and conditional compilation.

Compiler
--------
- [Rustc now respects the `-C codegen-units` flag in incremental mode.][70156]
  Additionally when in incremental mode rustc defaults to 256 codegen units.
- [Refactored `catch_unwind`, to have zero-cost unless unwinding is enabled and
  a panic is thrown.][67502]
- [Added tier 3\* support for the `aarch64-unknown-none` and
  `aarch64-unknown-none-softfloat` targets.][68334]
- [Added tier 3 support for `arm64-apple-tvos` and
  `x86_64-apple-tvos` targets.][68191]

Libraries
---------
- [Special cased `vec![]` to map directly to `Vec::new()`.][70632] This allows
  `vec![]` to be able to be used in `const` contexts.
- [`convert::Infallible` now implements `Hash`.][70281]
- [`OsString` now implements `DerefMut` and `IndexMut` returning
  a `&mut OsStr`.][70048]
- [Unicode 13 is now supported.][69929]
- [`String` now implements `From<&mut str>`.][69661]
- [`IoSlice` now implements `Copy`.][69403]
- [`Vec<T>` now implements `From<[T; N]>`.][68692] Where `N` is less than 32.
- [`proc_macro::LexError` now implements `fmt::Display` and `Error`.][68899]
- [`from_le_bytes`, `to_le_bytes`, `from_be_bytes`, `to_be_bytes`,
  `from_ne_bytes`, and `to_ne_bytes` methods are now `const` for all
  integer types.][69373]

Stabilized APIs
---------------
- [`PathBuf::with_capacity`]
- [`PathBuf::capacity`]
- [`PathBuf::clear`]
- [`PathBuf::reserve`]
- [`PathBuf::reserve_exact`]
- [`PathBuf::shrink_to_fit`]
- [`f32::to_int_unchecked`]
- [`f64::to_int_unchecked`]
- [`Layout::align_to`]
- [`Layout::pad_to_align`]
- [`Layout::array`]
- [`Layout::extend`]

Cargo
-----
- [Added the `cargo tree` command which will print a tree graph of
  your dependencies.][cargo/8062] E.g.
  ```
    mdbook v0.3.2 (/Users/src/rust/mdbook)
  +-- ammonia v3.0.0
  |   +-- html5ever v0.24.0
  |   |   +-- log v0.4.8
  |   |   |   +-- cfg-if v0.1.9
  |   |   +-- mac v0.1.1
  |   |   +-- markup5ever v0.9.0
  |   |       +-- log v0.4.8 (*)
  |   |       +-- phf v0.7.24
  |   |       |   +-- phf_shared v0.7.24
  |   |       |       +-- siphasher v0.2.3
  |   |       |       +-- unicase v1.4.2
  |   |       |           [build-dependencies]
  |   |       |           +-- version_check v0.1.5
  ...
  ```
  You can also display dependencies on multiple versions of the same crate with
  `cargo tree -d` (short for `cargo tree --duplicates`).

Misc
----
- [Rustdoc now allows you to specify `--crate-version` to have rustdoc include
  the version in the sidebar.][69494]

Compatibility Notes
-------------------
- [Rustc now correctly generates static libraries on Windows GNU targets with
  the `.a` extension, rather than the previous `.lib`.][70937]
- [Removed the `-C no_integrated_as` flag from rustc.][70345]
- [The `file_name` property in JSON output of macro errors now points the actual
  source file rather than the previous format of `<NAME macros>`.][70969]
  **Note:** this may not point a file that actually exists on the user's system.
- [The minimum required external LLVM version has been bumped to LLVM 8.][71147]
- [`mem::{zeroed, uninitialised}` will now panic when used with types that do
  not allow zero initialization such as `NonZeroU8`.][66059] This was
  previously a warning.
- [In 1.45.0 (the next release) converting a `f64` to `u32` using the `as`
  operator has been defined as a saturating operation.][71269] This was
  previously undefined behaviour, you can use the `{f64, f32}::to_int_unchecked`
  methods to continue using the current behaviour which may desirable in rare
  performance sensitive situations.

Internal Only
-------------
These changes provide no direct user facing benefits, but represent significant
improvements to the internals and overall performance of rustc and
related tools.

- [dep_graph Avoid allocating a set on when the number reads are small.][69778]
- [Replace big JS dict with JSON parsing.][71250]

[69373]: rust-lang/rust#69373
[66059]: rust-lang/rust#66059
[68191]: rust-lang/rust#68191
[68899]: rust-lang/rust#68899
[71147]: rust-lang/rust#71147
[71250]: rust-lang/rust#71250
[70937]: rust-lang/rust#70937
[70969]: rust-lang/rust#70969
[70632]: rust-lang/rust#70632
[70281]: rust-lang/rust#70281
[70345]: rust-lang/rust#70345
[70048]: rust-lang/rust#70048
[70081]: rust-lang/rust#70081
[70156]: rust-lang/rust#70156
[71269]: rust-lang/rust#71269
[69838]: rust-lang/rust#69838
[69929]: rust-lang/rust#69929
[69661]: rust-lang/rust#69661
[69778]: rust-lang/rust#69778
[69494]: rust-lang/rust#69494
[69403]: rust-lang/rust#69403
[69033]: rust-lang/rust#69033
[68692]: rust-lang/rust#68692
[68334]: rust-lang/rust#68334
[67502]: rust-lang/rust#67502
[cargo/8062]: rust-lang/cargo#8062
[`PathBuf::with_capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.with_capacity
[`PathBuf::capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.capacity
[`PathBuf::clear`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.clear
[`PathBuf::reserve`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve
[`PathBuf::reserve_exact`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve_exact
[`PathBuf::shrink_to_fit`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.shrink_to_fit
[`f32::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_int_unchecked
[`f64::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_int_unchecked
[`Layout::align_to`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.align_to
[`Layout::pad_to_align`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.pad_to_align
[`Layout::array`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.array
[`Layout::extend`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.extend
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