@SuperQ I think initial allocation when we create the collector is fine, right? We should just make sure not to allocate during scrape?

Yes, but this should also help with the AST-based doc generator that people are working on.

I can't really say that I am a fan of this change. It heavily pollutes an already-crowded global namespace in the collector package. I was already going to propose that each collector should be split out into a separate package (perhaps in a v2) because of this overcrowding.

Since the collectors are essentially singletons, if the objective was to make the descriptions more easily discoverable by AST, why not a compromise like declaring package-level collector vars (with the descriptions still as struct members)? e.g.

type arpCollector struct {
    fs           procfs.FS
    deviceFilter deviceFilter
    entries      *prometheus.Desc
    logger       *slog.Logger
}

var (
    arpCollector = arpCollector{
        entries: prometheus.NewDesc(...),
    }
)

The init() function would still need to take care of initializing stuff like fs, logger etc, but the descriptions would be declared at compile-time and should be traversable by AST.

Alternatively, how about adding something like a Document() method to the Collector interface, so that collectors must be self-documenting?