Conversion results unreliable for array schemas in formData parameters with multipart/form-data content type

[ghost]

When in an OpenAPIv2 file, an operation contains a parameter in: formData that has an array schema and the request's body is specified to have Content-Type: multipart/form-data, the Mermade produced OpenAPIv3 equivalent ignores the collectionFormat property. It has been stated in

• Encoding is not exploding a array property in requestBody in swagger-ui. swagger-api/swagger-ui#5106
• Submit An Array of Integer Elements In formdata swagger-api/swagger-ui#4741 especially the comment from 24 Aug 2018
• broken curl commands for formData with collectionFormat=multi swagger-api/swagger-ui#3838
  that the OpenAPIv3 spec is not clear about which serialization is used for such parameters.

Until this is fixed, the Mermade converter should signal an error "don't know how to convert in:formData parameter with array schema in Content-Type: multipart/form-data".

Checklist

• Conversion: I have checked my source definition is valid OpenAPI 2.0
• Conversion: On valid OpenAPI 2.0 input, the conversion looks wrong

Detailed Description

Assume an operation with Content-Type: multipart/form-data.

In OpenAPIv2 the serialization of parameters that have an array schema is guided by the collectionFormat property.

In OpenAPIv3, on the other hand, such parameters are first-level properties in the schema of the mediaType of the content of the requestBody.
The important sections here in the OpenAPIv3 spec https://github.com/OAI/OpenAPI-Specification/blob/676b48d8385244d5b02a9cfe40059d4a41f329cc/versions/3.0.2.md are:

• Encoding object
• Special Considerations for multipart Content

In particular, the serialization is specified through an encoding object outside the schema object, but in this object the properties style and explode are ignored for Content-Type: multipart/form-data.

I have prepared 4 test cases.

$ swagger2openapi -o form-multipart-parameter-array-of-strings-csv.v3m.json form-multipart-parameter-array-of-strings-csv.v2.json

$ swagger2openapi -o form-multipart-parameter-array-of-strings-ssv.v3m.json form-multipart-parameter-array-of-strings-ssv.v2.json
{ S2OError: collectionFormat:ssv is no longer supported except for in:query parameters
    at throwError (/openapi/node_modules/swagger2openapi/index.js:39:15)
    at throwOrWarn (/openapi/node_modules/swagger2openapi/index.js:54:9)
    at processParameter (/openapi/node_modules/swagger2openapi/index.js:564:21)
    at processPaths (/openapi/node_modules/swagger2openapi/index.js:936:30)
    at main (/openapi/node_modules/swagger2openapi/index.js:1170:5)
    at /openapi/node_modules/swagger2openapi/index.js:1505:13 name: 'S2OError' }

$ swagger2openapi -o form-multipart-parameter-array-of-strings-pipes.v3m.json form-multipart-parameter-array-of-strings-pipes.v2.json
{ S2OError: collectionFormat:pipes is no longer supported except for in:query parameters
    at throwError (/openapi/node_modules/swagger2openapi/index.js:39:15)
    at throwOrWarn (/openapi/node_modules/swagger2openapi/index.js:54:9)
    at processParameter (/openapi/node_modules/swagger2openapi/index.js:572:21)
    at processPaths (/openapi/node_modules/swagger2openapi/index.js:936:30)
    at main (/openapi/node_modules/swagger2openapi/index.js:1170:5)
    at /openapi/node_modules/swagger2openapi/index.js:1505:13 name: 'S2OError' }

$ swagger2openapi -o form-multipart-parameter-array-of-strings-multi.v3m.json form-multipart-parameter-array-of-strings-multi.v2.json

All should provide the same error message.

Other stuff

Version: swagger2openapi-5.3.0

form-multipart-parameter-array-of-strings-csv.v2.json.gz
form-multipart-parameter-array-of-strings-ssv.v2.json.gz
form-multipart-parameter-array-of-strings-pipes.v2.json.gz
form-multipart-parameter-array-of-strings-multi.v2.json.gz