`OpenAPI.Spec.merge/2` doesn't merge paths resulting in `paths: nil`

[florius0]

When running generation with additional_files, i.e.:

config :oapi_generator,
  tink: [
    reader: [
      file: "spec.yaml",
      additional_files: ["spec.additional.yaml"]
    ],
    naming: [
      base_module: Service,
      default_operation_module: Operation,
      operation_use_tags: true,
      field_casing: :snake
    ],
    output: [
      base_module: Service,
      location: "lib/service",
      default_client: Service.Client,
      operation_use: Service.Encoder,
      extra_fields: [:__meta__]
    ]
  ]

OpenAPI.Spec.merge/2's second clause is being called, and it doesn't set paths in resulting spec.

 @spec merge(t | nil, t) :: t
  defp merge(nil, spec_two), do: spec_two

  defp merge(spec_one, spec_two) do
    %__MODULE__{
      openapi: openapi_one,
      info: info_one,
      servers: servers_one,
      components: components_one,
      security: security_one,
      tags: tags_one,
      external_docs: external_docs_one
    } = spec_one

    %__MODULE__{
      servers: servers_two,
      components: components_two,
      security: security_two,
      tags: tags_two
    } = spec_two

    %__MODULE__{
      openapi: openapi_one,
      info: info_one,
      servers: servers_one ++ servers_two,
      components: Components.merge(components_one, components_two),
      security: security_one ++ security_two,
      tags: tags_one ++ tags_two,
      external_docs: external_docs_one
    }
  end

IMO we should merge Path.Item's, smth like:

...
path_items: Map.merge(paths_one, paths_two, Path.Item.merge/3)
...

I'll implement it shortly.

[aj-foster]

Hi @florius0, thanks for reporting this and for the PR. Do you have an example spec for this, or are the additional files created by you? I'd love to take a look, because there might be other places in the code where I made some bad assumptions about how multiple files should come together.

[florius0]

Hi, I don't suppose that I should share the real specs I got this error on, they are some 30k LOC :D, but I may be able to write example specs this week