Hi,
There is a problem using lifetimes, notated with a single tick. Since there is no second tick, all source code behind the operator is processed as a string.
\begin{lstlisting}[
language=Rust,
style=boxed,
]
fn foo() -> Result<u32, &'static str> {
Ok(42)
}
\end{lstlisting}
Result:

Best,
Roman