no-panic 0.1.12

Attribute macro to require that the compiler prove a function can't ever panic.
no-panic-0.1.12 doesn't have any documentation.

#[no_panic]

Build Status Latest Version

A Rust attribute macro to require that the compiler prove a function can't ever panic.

[dependencies]
no-panic = "0.1"
use no_panic::no_panic;

#[no_panic]
fn demo(s: &str) -> &str {
    &s[1..]
}

fn main() {
    println!("{}", demo("input string"));
}

If the function does panic (or the compiler fails to prove that the function cannot panic), the program fails to compile with a linker error that identifies the function name. Let's trigger that by passing a string that cannot be sliced at the first byte:

fn main() {
    println!("{}", demo("\u{1f980}input string"));
}
   Compiling no-panic-demo v0.0.1
error: linking with `cc` failed: exit code: 1
  |
  = note: /no-panic-demo/target/release/deps/no_panic_demo-7170785b672ae322.no_p
anic_demo1-cba7f4b666ccdbcbbf02b7348e5df1b2.rs.rcgu.o: In function `_$LT$no_pani
c_demo..demo..__NoPanic$u20$as$u20$core..ops..drop..Drop$GT$::drop::h72f8f423002
b8d9f':
          no_panic_demo1-cba7f4b666ccdbcbbf02b7348e5df1b2.rs:(.text._ZN72_$LT$no
_panic_demo..demo..__NoPanic$u20$as$u20$core..ops..drop..Drop$GT$4drop17h72f8f42
3002b8d9fE+0x2): undefined reference to `

          ERROR[no-panic]: detected panic in function `demo`
          '
          collect2: error: ld returned 1 exit status

The error is not stellar but notice the ERROR[no-panic] part at the end that provides the name of the offending function.

Compiler support: requires rustc 1.31+

Caveats

  • Functions that require some amount of optimization to prove that they do not panic may no longer compile in debug mode after being marked #[no_panic].

  • Panic detection happens at link time across the entire dependency graph, so any Cargo commands that do not invoke a linker will not trigger panic detection. This includes cargo build of library crates and cargo check of binary and library crates.

  • The attribute is useless in code built with panic = "abort".

If you find that code requires optimization to pass #[no_panic], either make no-panic an optional dependency that you only enable in release builds, or add a section like the following to Cargo.toml to enable very basic optimization in debug builds.

[profile.dev]
opt-level = 1

Acknowledgments

The linker error technique is based on Kixunil's crate dont_panic. Check out that crate for other convenient ways to require absence of panics.

License