rust/tests/mir-opt/pre-codegen/try_identity.rs

// skip-filecheck
//@ compile-flags: -O -C debuginfo=0 -Zmir-opt-level=2

// Track the status of MIR optimizations simplifying `Ok(res?)` for both the old and new desugarings
// of that syntax.

use std::ops::ControlFlow;

// EMIT_MIR try_identity.new.PreCodegen.after.mir
fn new<T, E>(x: Result<T, E>) -> Result<T, E> {
    Ok(
        match {
            match x {
                Ok(v) => ControlFlow::Continue(v),
                Err(e) => ControlFlow::Break(e),
            }
        } {
            ControlFlow::Continue(v) => v,
            ControlFlow::Break(e) => return Err(e),
        },
    )
}

// EMIT_MIR try_identity.old.PreCodegen.after.mir
fn old<T, E>(x: Result<T, E>) -> Result<T, E> {
    Ok(match x {
        Ok(v) => v,
        Err(e) => return Err(e),
    })
}

fn main() {
    let _ = new::<(), ()>(Ok(()));
    let _ = old::<(), ()>(Ok(()));
}