Can't generate an enum with value "null" or "NULL"

[bgolding355]

The problem

If you provide an openAPI spec:

openapi: "3.0.0"
info:
  version: 1.0.0
  title: some title
paths:
  /some-path:
    get:
      responses:
        '200':
          description: some description
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/NullEnum'
components:
  schemas:
    NullEnum:
      type: object
      properties:
        someEnum:
          type: string
          enum:
            - null
            - NULL
            - parses_correctly

with a config file:

# yaml-language-server: $schema=https://raw.githubusercontent.com/deepmap/oapi-codegen/HEAD/configuration-schema.json

package: example
output: api.gen.go
generate:
  models: true

Then the generated code looks like:

// Package example provides primitives to interact with the openapi HTTP API.
//
// Code generated by github.com/oapi-codegen/oapi-codegen/v2 version v2.4.1 DO NOT EDIT.
package example

// Defines values for NullEnumSomeEnum.
const (
	LessThannil     NullEnumSomeEnum = "<nil>"
	ParsesCorrectly NullEnumSomeEnum = "parses_correctly"
)

// NullEnum defines model for NullEnum.
type NullEnum struct {
	SomeEnum *NullEnumSomeEnum `json:"someEnum,omitempty"`
}

// NullEnumSomeEnum defines model for NullEnum.SomeEnum.
type NullEnumSomeEnum string

So as you can see, the enum:

type: string
enum:
  - null
  - NULL
  - parses_correctly

Is rendered as:

// Defines values for NullEnumSomeEnum.
const (
	LessThannil     NullEnumSomeEnum = "<nil>"
	ParsesCorrectly NullEnumSomeEnum = "parses_correctly"
)

Which is not what I would expect.

My setup

go version: 1.24.0
oapi-codegen version: v2.4.1
generate command: go:generate go tool github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen -config cfg.yaml api.yaml

[bgolding355]

As a workaround you can wrap the string null in double quotes. So:

someEnum:
  type: string
  enum:
    - "null"

Generates a reasonable type. But the fact that you need to wrap this value in double-quotes, but don't need to for other values is less then ideal

[psunderhaus-alto]

I've been experiencing this exact issue since moving from deepmap/[email protected] to oapi-codegen/[email protected].

If I include an enum in my spec for a property that is nullable, and I follow the instructions from OpenAPI on this scenario to include a null entry in the enum listing, oapi-codegen produces variable names that appear to be matching on the < symbol used as the value "<nil>" in the const definition.

Example generated code output:

// Defines values for SomeEnum.
const (
	SomeEnumExample1    SomeEnum = "accredited-investor"
	SomeEnumLessThannil SomeEnum = "<nil>"
)

As another workaround, you can specify an x-enum-varnames to override the automatically generated variable names for your enum values.

someEnum:
  type: string
  nullable: true
  enum:
    - example-1
    - null
  x-enum-varnames:
    - Example1
    - Nil

[jamietanna]

the fact that you need to wrap this value in double-quotes, but don't need to for other values is less then ideal

This seems like it's a YAML issue, rather than oapi-codegen 🤔

That being said, if it's then generating <nil> then yes that's likely to be a bug!

[bgolding355]

the fact that you need to wrap this value in double-quotes, but don't need to for other values is less then ideal

This seems like it's a YAML issue, rather than oapi-codegen 🤔

That being said, if it's then generating <nil> then yes that's likely to be a bug!

@jamietanna Given that if you wrap the string null in quotes (i.e. "null" > null) it generates a reasonable type. Could the solution be:

1. If a user provides an enum with value null oapi-codegen fails with a message saying that this is not a valid type and they need to use null instead OR
2. oapi-codegen implicitly wraps the enum value null (case-insensitive) in quotes ?