[BUG] [Dart] Problem with enum generation, when enum value is a symbol, like the character %

Created by: ka-zo

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?

Description

There is a problem with the generated dart code for enums, as those enums in the openapi.json file, where the enum value is a special character, like %, will end up in the generated dart code with the name _.

openapi-generator version

4.3.1

Support file contents

The openapi.json file content is shown below. The part of the specification that results in the problematic dart code is components/schemas/PercentileUnit/enum.

{
    "openapi": "3.0.2",
    "info": {
        "title": "FastAPI",
        "version": "0.1.0"
    },
    "paths": {
        "/enum/": {
            "get": {
                "tags": [
                    "Administration"
                ],
                "summary": "Test Enum",
                "description": "Test get enum.",
                "operationId": "test_enum_enum__get",
                "responses": {
                    "200": {
                        "description": "Successful Response",
                        "content": {
                            "application/json": {
                                "schema": {
                                    "$ref": "#/components/schemas/PercentileValue"
                                }
                            }
                        }
                    }
                }
            }
        }
    },
    "components": {
        "schemas": {
            "PercentileUnit": {
                "title": "PercentileUnit",
                "enum": [
                    "%"
                ],
                "type": "string",
                "description": "An enumeration."
            },
            "PercentileValue": {
                "title": "PercentileValue",
                "required": [
                    "unit",
                    "value"
                ],
                "type": "object",
                "properties": {
                    "unit": {
                        "$ref": "#/components/schemas/PercentileUnit"
                    },
                    "value": {
                        "title": "Value",
                        "maximum": 97,
                        "minimum": 3,
                        "type": "number",
                        "description": "Value of the percentile."
                    }
                }
            }
        }
    }
}

The flutterconfig-dart.json file is the following:

{
    "pubAuthor": "Agent Moo",
    "pubDescription": "Security level BBR (Burn Before Read)",
    "pubName": "PeekAMooOpenAPI",
    "browserClient": false,
    "useEnumExtension": true
}

The generated percentile_unit.dart model file that has an issue is the following:

part of PeekAMooOpenAPI.api;

class PercentileUnit {
  /// The underlying value of this enum member.
  final String value;

  const PercentileUnit._internal(this.value);

  /// An enumeration.
  static const PercentileUnit _ = const PercentileUnit._internal("%");

  static PercentileUnit fromJson(String value) {
    return new PercentileUnitTypeTransformer().decode(value);
  }
  
  static List<PercentileUnit> listFromJson(List<dynamic> json) {
    return json == null ? new List<PercentileUnit>() : json.map((value) => PercentileUnit.fromJson(value)).toList();
  }
}

class PercentileUnitTypeTransformer {

  dynamic encode(PercentileUnit data) {
    return data.value;
  }

  PercentileUnit decode(dynamic data) {
    switch (data) {
      case "%": return PercentileUnit._;
      default: throw('Unknown enum value to decode: $data');
    }
  }
}

The problem I have with the code above:

  /// An enumeration.
  static const PercentileUnit _ = const PercentileUnit._internal("%");

Dart code outside the generated dart package cannot reference enume value with PercentileUnit._. Somehow special characters, like % should be translated to a string, that can be used as valid parameter name in Dart, because currently the special characters are translated to an empty string. Most likely the problem is with the content of {{{name}}} in https://github.com/OpenAPITools/openapi-generator/blob/b6091571aa4a93d086f8618bdf3d12092f24d157/modules/openapi-generator/src/main/resources/dart/enum.mustache#L13 and in https://github.com/OpenAPITools/openapi-generator/blob/b6091571aa4a93d086f8618bdf3d12092f24d157/modules/openapi-generator/src/main/resources/dart/enum.mustache#L30.

Generation Details

The Dart code is generated on Windows with the following shell command.

java -jar openapi-generator-cli-4.3.1.jar generate -i .\openapi.json -g dart -o .\peekamoo-openapi -c flutterconfig-dart.json

Steps to reproduce

Execute shell command written above, using the support files included above, then check the generated dart code in .\peekamoo-openapi\lib\model\percentile_unit.dart.

Related issues/PRs

none

Suggest a fix

The content of {{{name}}} in https://github.com/OpenAPITools/openapi-generator/blob/b6091571aa4a93d086f8618bdf3d12092f24d157/modules/openapi-generator/src/main/resources/dart/enum.mustache#L13 and in https://github.com/OpenAPITools/openapi-generator/blob/b6091571aa4a93d086f8618bdf3d12092f24d157/modules/openapi-generator/src/main/resources/dart/enum.mustache#L30 should not be simply _ when the enum value is a special character.