Rust 1.47: What's New, Release History & Support Lifecycle

What Is New in Rust 1.47

How does Rust 1.47 improve support for arrays of any length?

Rust 1.47 extends the standard library so that traits such as Debug are implemented for arrays of any compile-time length, not just 0-32.

In practice this means code like:

fn main() {
    let xs = [0; 34];
    println!("{:?}", xs);
}

now compiles and prints the array, whereas older versions emitted an error about LengthAtMost32. The implementation uses the compiler's const-generic support, paving the way for future generic-over-length APIs.

What changes make debugging panics easier in Rust 1.47?

Rust 1.47 shortens the default panic backtrace to show only the frames that are most relevant to the panic location.

• The backtrace now starts with the panic entry point, the user's function, and the core call site.
• All the internal library frames that previously cluttered the output are omitted unless RUST_BACKTRACE=full is set.

This matters if you need to quickly locate the source of a crash without sifting through dozens of lines of noise.

Which standard library APIs became const in Rust 1.47 and why does it matter?

Rust 1.47 marks a large set of integer and character helper methods as const, allowing them to be used in compile-time contexts.

• All NonZero constructors.
• Checked arithmetic: checked_add, checked_sub, checked_mul, checked_neg, checked_shl, checked_shr.
• Saturating arithmetic: saturating_add, saturating_sub, saturating_mul, saturating_abs, saturating_neg.
• Sign handling: signum for signed integers.
• ASCII classification methods on char and u8 (e.g., is_ascii_alphabetic, is_ascii_digit, etc.).

Having these as const means you can compute values at compile time, reducing runtime overhead and enabling more expressive const fn implementations.

What toolchain upgrades are included in Rust 1.47?

Rust 1.47 ships with several behind-the-scenes improvements that affect build performance and security.

• LLVM upgraded to version 11, bringing newer optimizations and better codegen support.
• New -C control-flow-guard flag enables Windows Control Flow Guard hardening; other platforms ignore the flag.
• Rustdoc now includes the Ayu visual theme, giving documentation a fresh look.

Most teams will see no breaking changes, but the LLVM bump may affect custom toolchains that pin an older LLVM version.