Rust 1.77: What's New, Release History & Support Lifecycle

What Is New in Rust 1.77

How do C-string literals simplify FFI in Rust?

The new c"..." literal creates a &'static CStr with compile-time validation of interior nul bytes.

• Write c"hello" instead of manually constructing a CStr or using CString::new.
• The compiler guarantees the string ends with a single nul byte and contains no interior nul, preventing undefined behaviour at runtime.
• This matters if your crate talks to C APIs, Windows DLLs, or any foreign interface that expects nul-terminated strings.

use std::ffi::CStr;

extern "C" {
    fn puts(s: *const i8);
}

fn greet() {
    unsafe { puts(c"Hello from Rust!\0".as_ptr()) };
}

Can async functions be recursive in Rust 1.77?

Yes, async functions can now call themselves as long as the recursion is indirected to keep the future size bounded.

• The compiler lifted the previous limitation that treated self-calls as infinite size.
• Typical pattern: box the recursive call with Box::pin or use a custom future type.
• This is useful for algorithms like async Fibonacci, tree traversal, or state-machine loops.

async fn fib(n: u32) -> u32 {
    match n {
        0 | 1 => 1,
        _ => Box::pin(fib(n - 1)).await + Box::pin(fib(n - 2)).await,
    }
}

What is offset_of! and when should I use it?

The offset_of! macro returns the byte offset of a public struct field without needing an instance.

• It expands to a usize constant, safe to use in const contexts.
• Ideal for low-level interop, custom memory layout calculations, or implementing safe wrappers around raw pointers.
• Watch out for changes in struct layout across compiler versions; the macro reflects the layout of the current compilation target.

#[repr(C)]
struct Header {
    magic: u32,
    version: u16,
    flags: u16,
}

const VERSION_OFFSET: usize = offset_of!(Header, version);

How does the default strip setting affect release builds?

Release profiles that disable debug info now automatically strip debug symbols from the final binary.

• This reduces binary size for statically linked executables, especially when the standard library is compiled with debuginfo.
• If you need full debug information for profiling, re-enable it with debug = 1 (or higher) in the relevant Cargo profile.
• Most CI pipelines benefit from smaller artifacts without sacrificing runtime performance.