PR #1501: Better Error Messages for Linearity Violations in Structs

Today, I wanted to mention another Quantinuum Guppy contribution: improving error messages for linearity violations in quantum data structures.

When developers organized quantum data into structures (like grouping multiple qubits together), they would sometimes move one piece of data out. Then, when they tried to use the whole structure, Guppy’s error message would point at the wrong place — making it confusing to debug.

In PR #1501, I made the error messages point developers to the right place. Instead of pointing at internal data, error messages now explain which specific piece inside the structure caused the problem. This makes it clear both where the violation happened and which member caused it.

Good error messages can mean the difference between fixing a bug in 5 minutes versus spending hours trying to understand what went wrong. This is especially important in quantum programming, where developers are learning unfamiliar concepts like linearity — myself included.

As always, I appreciate the Guppy contributors at Quantinuum for their collaboration.

For more technical details, refer to PR #1501.