probable compiler bug results in rust_decimal Ord not working and a panic

[hydra]

I've not found a way to minimal compiler test case, but I do have a repeatable example and video evidence in the form of debugger step-through session.

Code

here's a snippet of the code:

                let l = &row_l.placement_state.unit_position.x;
                let r = &row_r.placement_state.unit_position.x;
                println!("l: {:?}, r: {:?}", l, r);
                let ordering1 = l.cmp(r);
                println!("ordering1: {:?}", ordering1);
                
                println!("l: {:?}, r: {:?}", &row_l.placement_state.unit_position.x, &row_r.placement_state.unit_position.x);
                let ordering2 = row_l
                    .placement_state
                    .unit_position
                    .x
                    .cmp(&row_r.placement_state.placement.x);

                println!("ordering2: {:?}", ordering2);

                if ordering1 != ordering2 {
                    panic!("ordering1: {:?}, ordering2: {:?}", ordering1, ordering2);  // <-- the above code causes this panic to execute.  if this check is removed, rust 1.81 and onwards will cause a panic since this code is used in `sort_by`.
                }
                ordering1

this prints out:

l: 114.5, r: 117
ordering1: Less
l: 114.5, r: 117
ordering2: Greater

it should print out:

l: 114.5, r: 117
ordering1: Less
l: 114.5, r: 117
ordering2: Less

The commit with the above is here:

MakerPnP/makerpnp@63b0bbe

The video walkthough is here:

https://www.youtube.com/watch?v=0bD76RJmrgI

The original bug report against rust_decimal is here, though I do not currently think there's anything wrong with the rust_decimal Ord implementation.

paupino/rust-decimal#741

Meta

rustc --version --verbose:

rustc 1.87.0 (17067e9ac 2025-05-09)
binary: rustc
commit-hash: 17067e9ac6d7ecb70e50f92c1944e545188d2359
commit-date: 2025-05-09
host: x86_64-pc-windows-msvc
release: 1.87.0
LLVM version: 20.1.1

Error output

N/A

[hydra]

never mind, an edit ___location was missed in recent change to the code that showed unit positions instead of placement.

this line:

let ordering2 = row_l
                    .placement_state
                    .unit_position
                    .x
                    .cmp(&row_r.placement_state.placement.x);

should have read:

let ordering2 = row_l
                    .placement_state
                    .unit_position
                    .x
                    .cmp(&row_r.placement_state.unit_position.x);

quite how I missed that I don't know, long day I suppose.

sorry for the noise, and thanks to beelzebufo 𓆏 (evil frog) and cratermoon on the Rust Programming Longuage Community discord for pointing out my failure! https://discord.com/channels/273534239310479360/273541522815713281/1400181518323941438

🤦