While better, a person modifying PizzaDetails might or might not expect this change to affect the downstream pizza deduplication logic (wherever it got sprinkled throughout the code). They might not even know that it exists.
Ideally, imho, a struct is a dumb data holder - it is there to pass associated pieces of data together (or hold a complex unavoidable state change hidden from the user like Arc or Mutex).
All that is to say that adding a field to an existing struct and possibly populating it sparsely in some remote piece of code should not changed existing behavior.
I wonder whether there's a way to communicate to whoever makes changes to the pizza details struct that it might have unintended consequences down the line.
Should one wrap PizzaDetails with PizzaComparator? Or better even provide it as a field in PizzaOrder? Or we are running into Java-esq territory of PizzaComparatorBuilderDefaultsConstructorFactory?
Should we introduce a domain specific PizzaFlavor right under PizzaDetails that copies over relevant fields from PizzaDetails, and PizzaOrder compares two orders by constructing and comparing their flavours instead? A lot of boilerplate.. but what is being considered important to the pizza flavor is being explicitly marked.
In a prod codebase I'd annotate this code with "if change X chaange Y" pre submit hook - this constraint appears to be external to the language itself and live in the domain of "code changes over time". Protobufs successfully folded versioning into the language itself though. Protobufs also have field annotations, "{important_to_flavour=true}" field annotation would be useful here.