misra_gries_edge_color panicking on UnGraphMap

[willchet]

Information

• rustworkx version: 0.17.1
• Python version: N/A
• Rust version: 1.96.0-nightly (900485642 2026-04-08)
• Operating system: Fedora Linux 44 (Workstation Edition)

What is the current behavior?

When calling misra_gries_edge_color, I get a panic when passing an UnGraphMap. The panic occurs at rustworkx-core-0.17.1/src/coloring.rs:711:21 with message "edge not found".

The issue vanishes if I convert it to an UnGraph first. However, the documentation does not mention this as being a requirement.

What is the expected behavior?

The function should return DictMap with the coloring without panic.

Steps to reproduce the problem

Use the MWE:

use petgraph::prelude::UnGraphMap;
use rustworkx_core::coloring::misra_gries_edge_color;

fn main() {
    let mut my_graph: UnGraphMap<&str, &str> = UnGraphMap::new();

    my_graph.add_edge("Node 1", "Node 2", "Edge 1");
    my_graph.add_edge("Node 2", "Node 3", "Edge 2");

    misra_gries_edge_color(&my_graph);
}

[willchet]

If you would like more details, let me know! This was my first time using rustworkx-core, so I am not as familiar with it as other users may be.

[IvanIsCoding]

I think your bug is legitimate and a PR fixing the issue is welcome.

I think the main reason behind the bug is: our Python API uses mostly https://docs.rs/petgraph/latest/petgraph/stable_graph/struct.StableGraph.html. So I'd rank our support as excellent for StableGraph, ok for Graph, and everything else after that is something you should consider covering in some sort of tests to confirm it matches the expected behavior. In this case, at least we panicked instead of returning garbage, I guess.

[willchet]

As of now, I don't think I have the bandwidth to fix the issue, but I figure this issue can be left open in case someone else can solve it (or in case I can revisit it later). In the meantime, it might be worthwhile to users of the Rust crate to mention in the crate-level documentation that support is primarily for StableGraph.