v3: allow extensions next to $ref in SchemaRef

[paulmach]

I would like to extent SchemaRef to have a Extensions or RefExtensions to capture extensions next to $ref.

For example, if I have:

type: object
properties:
 id:
   $ref: "#/components/schemas/id"
   x-order: 1
 name:
   type: string

I would like to capture the x-order: 1 within SchemaRef.Extensions["x-order"]

Looking at the code it looks like it's "if $ref only capture $ref"

I don't think the openapi v3 spec official supports this but it would be very helpful.

My use-case is specifying the x-order, a new feature added to oapi-codegen. For example:

type: object
properties:
 start_port:
   $ref: "#/components/schemas/port"
   x-order: 0
 end_port:
   $ref: "#/components/schemas/port"
   x-order: 1

It works if you specify the x-order in the referenced object, but in the above it needs to be context dependent. A change would need to be made to oapi-codegen but it looks to be blocked by this issue.

If this change is okay, I can work on the PR.

[fenollp]

Oh my, thanks for noticing and reporting! This is definitely a bug / not wanted!
Looking forward to your PR.

[paulmach]

I created a pr to add Extension to SchemaRef. If this approach is agreed I can expand to all *Refs.

#901

[paulmach]

I have verified that #901 adds the support needed to fix my use-case in oapi-codegen