[BUG] [Dart] Non-string enum decode uses data.toString() without casting value to string

Created by: 0xNF

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

Enums that aren't strings are decoded with a check that includes toString(), but doesn't cast the enum value to a string, resulting in a compile error.

openapi-generator version

6.0.0

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  version: "1.1"
  title: Dart IntegerEnum Fail
servers:
  - url: 'localhost'
    variables:
      host:
        default: localhost
components:
  schemas:
    NonStringEnum:
      type: integer
      enum:
      - 1
      - 2
paths:
  /items:
    get:
      operationId: GetItems
      responses:
        "200":
          description: A list of Items
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/NonStringEnum'

Generation Details

  NonStringEnum? decode(dynamic data, {bool allowNull = true}) {
    if (data != null) {
      switch (data.toString()) {
        case 1: return NonStringEnum.number1;
        case 2: return NonStringEnum.number2;
        default:
          if (!allowNull) {
            throw ArgumentError('Unknown enum value to decode: $data');
          }
      }
    }
    return null;
  }

Compile error is at case 1: and case 2:. Because the raw values are used, even though the data was cast toString(), the types are mismatched and the compiler wont compile.

Steps to reproduce

1. java -jar ..\openapi-generator\modules\openapi-generator-cli\target\openapi-generator-cli.jar generate -i .\shadowspec.yaml -g dart -o string_enums

And then checkout string_enums/lib/model/non_string_enum.dart, line 71

Suggest a fix

1. Ensure that non-string enums are quoted when generating the decode function