Fix const keyword being used in OpenAPI 3.0.3 (#241)

[BITespresso]

Fixes issue #241 so that for OpenAPI 3.0.3 the const keyword gets replaced be a single valued enum.

[adamw]

is this correctly rendered, since in components we define both a const and an enum, and the const_and_enum.json file contains only one enum?

[BITespresso]

The reason is that in order to get rid of the const we need to replace the enum. As the Schema itself does not forbid to have a const and an enum defined for the same item (which of course makes not sense) we will just overwrite the enum with the value defined in const. Hence, what were two different things in the Schema (const and enum) will be reduced to just an enum in the JSON.

Does that make sense?

[BITespresso]

Or explained by example:

For this schemaComponent

schemaComponent("const and enum")(
  Schema(
    const = Some("const1").map(ExampleSingleValue(_)),
    `enum` = Some(List("enum1", "enum2").map(ExampleSingleValue(_)))
  )
)

the following would be the JSON for OpenAPI 3.1.0 (although it does not make sense to have something being an enum and const at the same time):

{
  "openapi" : "3.1.0",
  "info" : {
    "title" : "API",
    "version" : "1.0.0"
  },
  "components" : {
    "schemas" : {
      "const and enum" : {
        "description" : "const and enum",
        "enum" : [
          "enum1",
          "enum2"
        ],
        "const" : "const1"
      }
    }
  }
}

for OpenAPI 3.0.x this will be transformed to:

{
  "openapi" : "3.0.1",
  "info" : {
    "title" : "API",
    "version" : "1.0.0"
  },
  "components" : {
    "schemas" : {
      "const and enum" : {
        "description" : "const and enum",
        "enum" : [
          "const1"
        ]
      }
    }
  }
}

The above is only an edge case test. In reality it is more important to have the correct result for the "full 3.0 schema" and "full 3.1 schema" tests.

in "/spec/3.1/schema.json"

      "const" : {
        "const" : "const1",
        "description" : "const"
      },

versus in "/spec/3.0/schema.json"

      "const" : {
        "description" : "const",
        "enum" : [
          "const1"
        ]
      }

[adamw]

Ah ok the edge case mislead me :)

[adamw]

Thanks!