A Rust attribute macro to require that the compiler prove a function can't ever panic.
 = "0.1"
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:
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+
Functions that require some amount of optimization to prove that they do not panic may no longer compile in debug mode after being marked
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 buildof library crates and
cargo checkof 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
 = 1
If the code that you need to prove isn't panicking makes function calls to non-generic non-inline functions from a different crate, you may need thin LTO enabled for the linker to deduce those do not panic.
 = "thin"
If you want no_panic to just assume that some function you call doesn't panic,
and get Undefined Behavior if it does at runtime, see dtolnay/no-panic#16; try
wrapping that call in an
unsafe extern "C" wrapper.
The linker error technique is based on Kixunil's crate
out that crate for other convenient ways to require absence of panics.