Support custom route generators through the plugin system?

[amtellezfernandez]

Using a custom route source (an external routing service, hand-authored scenario routes) currently means editing core code: RouteGeneratorType is a closed enum and RouteGenerator.create() dispatches to the two built-in generators directly.

PLUGIN_SYSTEM.md states the direction for this kind of extension: "Any installed package can register models, configs, or tools without modifying the core codebase." Route generators aren't one of the extension points today, and I can't tell from the outside whether that's a deliberate boundary or just not built yet, hence a question before any PR.

If you'd take it, the shape I have in mind follows the doc's guideline that plugins extend components and never replace built-in ones: an alpasim.route_generators registry plus an optional route_generator_plugin config field that resolves through it when set. Unset keeps the enum dispatch untouched, so existing configs see no change. I would deliberately not migrate the two built-in generators to entry points in the same change; RouteGenerator is an ABC, and retrofitting a uniform construction contract onto both existing classes is more than this needs.

I have a working version of this, small and strictly additive, and can open a PR if the direction sounds right, or build a different shape if you'd draw the boundary elsewhere.

[mwatson-nvidia]

This is not a deliberate omission. The plugin idea was added relatively late in the development and so there are cases like this where we haven't changed over.

So, yes, we would welcome additional submissions, and maybe the only question I would ask is, does the work belong in a plugin or as a built-in route generation strategy?

[amtellezfernandez]

Thanks for the feedback! Regarding your question, I propose using plugins for project-specific route generators or integrations with external dependencies. Generally useful routing strategies can still be added as built-ins.

I’ve put together a proposal in #179 using AlpaSim’s existing plugin system. It adds an optional route_generator_plugin setting so external packages can provide a generator without changing the runtime factory. Leaving it unset keeps the existing built-in behavior.

The PR adds the extension point, not a new routing strategy, and includes documentation and tests. A shared registry for built-in and external generators could be cleaner eventually, but I’ve kept the built-ins unchanged for this first step.

Let me know what you think of this approach!