[BUG] Error during deserialization for elements with discriminator and mapping type name

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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

There is an exception during the deseralization of an element defined with a discriminator and a mapping type name, in the read(JsonReader) method of the generated model java class.

Failed deserialization for MetadataFieldAny: 5 classes match result, expected 1.
JSON: {"type":"int","value":1}

Multiple match was found while a discriminator was provided.

openapi-generator version

6.2.1

OpenAPI declaration file content or url

    MetadataField_Any:
      description: metadata field
      oneOf:
      - $ref: '#/components/schemas/BoolMeta'
      - $ref: '#/components/schemas/DateTimeMeta'
      - $ref: '#/components/schemas/DoubleMeta'
      - $ref: '#/components/schemas/IntMeta'
      - $ref: '#/components/schemas/MultipleDateTimeMeta'
      - $ref: '#/components/schemas/MultipleDoubleMeta'
      - $ref: '#/components/schemas/MultipleIntMeta'
      - $ref: '#/components/schemas/MultipleStringMeta'
      - $ref: '#/components/schemas/StringMeta'
      discriminator:
        propertyName: type
        mapping:
          bool: '#/components/schemas/BoolMeta'
          datetime: '#/components/schemas/DateTimeMeta'
          double: '#/components/schemas/DoubleMeta'
          int: '#/components/schemas/IntMeta'
          multidatetime: '#/components/schemas/MultipleDateTimeMeta'
          multidouble: '#/components/schemas/MultipleDoubleMeta'
          multiint: '#/components/schemas/MultipleIntMeta'
          multistring: '#/components/schemas/MultipleStringMeta'
          string: '#/components/schemas/StringMeta'

    BoolMeta:
      required:
      - value
      - type
      type: object
      properties:
        value:
          type: boolean
        type:
          type: string

    DateTimeMeta:
      required:
      - value
      - type
      type: object
      properties:
        value:
          type: string
          format: date-time
        type:
          type: string

    DoubleMeta:
      required:
      - value
      - type
      type: object
      properties:
        value:
          type: number
          format: double
        type:
          type: string

    IntMeta:
      required:
      - value
      - type
      type: object
      properties:
        value:
          type: integer
          format: int32
        type:
          type: string

    ...

Generation Details

Generated with maven plugin

This is an extract of the generated read method.

@Override
public MetadataFieldAny read(JsonReader in) throws IOException {
	Object deserialized = null;
	JsonObject jsonObject = elementAdapter.read(in).getAsJsonObject();

	int match = 0;
	ArrayList<String> errorMessages = new ArrayList<>();
	TypeAdapter actualAdapter = elementAdapter;

	// deserialize BoolMeta
	try {
		// validate the JSON object to see if any exception is thrown
		BoolMeta.validateJsonObject(jsonObject);
		actualAdapter = adapterBoolMeta;
		match++;
		log.log(Level.FINER, "Input data matches schema 'BoolMeta'");
	} catch (Exception e) {
		// deserialization failed, continue
		errorMessages.add(String.format("Deserialization for BoolMeta failed with `%s`.", e.getMessage()));
		log.log(Level.FINER, "Input data does not match schema 'BoolMeta'", e);
	}

	// deserialize DateTimeMeta
	try {
		// validate the JSON object to see if any exception is thrown
		DateTimeMeta.validateJsonObject(jsonObject);
		actualAdapter = adapterDateTimeMeta;
		match++;
		log.log(Level.FINER, "Input data matches schema 'DateTimeMeta'");
	} catch (Exception e) {
		// deserialization failed, continue
		errorMessages.add(String.format("Deserialization for DateTimeMeta failed with `%s`.", e.getMessage()));
		log.log(Level.FINER, "Input data does not match schema 'DateTimeMeta'", e);
	}

	...

	if (match == 1) {
		MetadataFieldAny ret = new MetadataFieldAny();
		ret.setActualInstance(actualAdapter.fromJsonTree(jsonObject));
		return ret;
	}

	throw new IOException(String.format("Failed deserialization for MetadataFieldAny: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonObject.toString()));
}

Steps to reproduce

1. Write an openapi file with an element with discriminator and a mapping type name
2. Generate the code with the maven plugin
3. Try to read the response containing the element

Related issues/PRs

Suggest a fix

Reproduce the issue with the YAML declaration and Maven plugin, then inspect the generated Java model's read(JsonReader) method shown in the report. Trace how the discriminator mapping is handled during oneOf deserialization. Done means the mapped type is selected without the multiple-match exception for the provided JSON.