Short-form of supergraph.yaml

[dbanty]

Description

Right now, if you want to introspect subgraphs for supergraph compose or dev --supergraph-config, you need to duplicate the routing URL:

subgraphs:
  products:
    routing_url: http://localhost:4001
    schema:
      subgraph_url: http://localhost:4001

There are certainly cases where you'll want to use separate URLs, but most cases it probably makes sense to assume they are the same. If schema is omitted, we could assume we should attempt introspection at routing_url.

Additionally, when no other config is needed, it might be best to have an even shorter form of this config file that looks something like this:

subgraphs:
  products: http://localhost:4001

This will all require changes over in federation-rs, but they will be used here, so the issue is here.

[WolffRuoff]

This behavior wouldn't be usable if the URLs are the same, but there are introspection headers. Maybe an alternative solution would be to have subgraph_url's default value be the routing_url value. That way, if you don't have any headers, it would still be:

subgraphs:
   products:
      routing_url: http://localhost:4001