Language

• You can now write open "from" range patterns (X..), which will start at X and will end at the maximum value of the integer.
• You can now explicitly import the prelude of different editions through std::prelude (e.g. use std::prelude::rust_2021::*;).

Compiler

• Added tier 3* support for powerpc64le-unknown-freebsd.

* Refer to Rust's platform support page for more information on Rust's tiered platform support.

Libraries

• Updated std's float parsing to use the Eisel-Lemire algorithm. These improvements should in general provide faster string parsing of floats, no longer reject certain valid floating point values, and reduce the produced code size for non-stripped artifacts.
• string::Drain now implements AsRef<str> and AsRef<[u8]>.

Stabilised APIs

• Bound::cloned
• Drain::as_str
• IntoInnerError::into_error
• IntoInnerError::into_parts
• MaybeUninit::assume_init_mut
• MaybeUninit::assume_init_ref
• MaybeUninit::write
• array::map
• ops::ControlFlow
• x86::_bittest
• x86::_bittestandcomplement
• x86::_bittestandreset
• x86::_bittestandset
• x86_64::_bittest64
• x86_64::_bittestandcomplement64
• x86_64::_bittestandreset64
• x86_64::_bittestandset64

The following previously stable functions are now const.

• str::from_utf8_unchecked

Cargo

• Cargo will now deduplicate compiler diagnostics to the terminal when invoking rustc in parallel such as when using cargo test.
• The package definition in cargo metadata now includes the "default_run" field from the manifest.
• Added cargo d as an alias for cargo doc.
• Added {lib} as formatting option for cargo tree to print the "lib_name" of packages.

Rustdoc

• Added "Go to item on exact match" search option.
• The "Implementors" section on traits no longer shows redundant method definitions.
• Trait implementations are toggled open by default. This should make the implementations more searchable by tools like CTRL+F in your browser.
• Intra-doc links should now correctly resolve associated items (e.g. methods) through type aliases.
• Traits which are marked with #[doc(hidden)] will no longer appear in the "Trait Implementations" section.

Compatibility Notes

• std functions that return an io::Error will no longer use the ErrorKind::Other variant. This is to better reflect that these kinds of errors could be categorised into newer more specific ErrorKind variants, and that they do not represent a user error.
• Using environment variable names with process::Command on Windows now behaves as expected. Previously using envionment variables with Command would cause them to be ASCII-uppercased.
• Rustdoc will now warn on using rustdoc lints that aren't prefixed with rustdoc::
• RUSTFLAGS is no longer set for build scripts. Build scripts should use CARGO_ENCODED_RUSTFLAGS instead. See the documentation for more details.