Reference in callback

[ShouheiNishi]

If multiple callback objects with same expression are exist, reference in some of these are not resolved by the loader.

package openapi3_test

import (
        "testing"

        "github.com/stretchr/testify/require"

        "github.com/getkin/kin-openapi/openapi3"
)

func TestXXX(t *testing.T) {

        loader := openapi3.NewLoader()

        doc, err := loader.LoadFromFile("testdata/issueNEW.yaml")
        require.NoError(t, err)

        err = doc.Validate(loader.Context)
        require.NoError(t, err)

        require.NotNil(t, (*doc.Paths["/test1"].Post.Callbacks["callback1"].Value)["{request.body#/callback}"].Post.RequestBody.Value.Content["application/json"].Schema.Value)
        require.NotNil(t, (*doc.Paths["/test2"].Post.Callbacks["callback2"].Value)["{request.body#/callback}"].Post.RequestBody.Value.Content["application/json"].Schema.Value)
}

openapi: 3.0.0
info:
  version: 0.0.1
  title: 'test'
paths:
  /test1:
    post:
      requestBody:
        content:
          application/json:
            schema:
              type: object
      responses:
        '200':
          description: 'test'
      callbacks:
        callback1:
          '{request.body#/callback}':
            post:
              requestBody:
                content:
                  application/json:
                    schema:
                      $ref: '#/components/schemas/test'
              responses:
                '200':
                  description: 'test'
  /test2:
    post:
      requestBody:
        content:
          application/json:
            schema:
              type: object
      responses:
        '200':
          description: 'test'
      callbacks:
        callback2:
          '{request.body#/callback}':
            post:
              requestBody:
                content:
                  application/json:
                    schema:
                      $ref: '#/components/schemas/test'
              responses:
                '200':
                  description: 'test'
components:
  schemas:
    test:
      type: string

[fenollp]

Note I've opened #756
I corrected '{request.body#/callback}' to '{$request.body#/callback}' (leading $) but the issue is still present (more: visiting order is not deterministic. cc #695 )

More investigation needed!