[BUG] [PHP] [Symfony] Several issues for parameters of type date-time

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

When I declare a parameter of with type: string and format: date-time and generate a symfony bundle with it, then I observe that queries on that endpoint get a 400 response with message This value should be of type string.

openapi-generator version

I've observed this behavior with openapi-generator 6.3.0, as well as on a version built from source with today's master branch (140d941d)

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: Test
  version: 0.0.1
paths:
  /my-route:
    get:
      summary: Get stuff
      parameters:
        - name: myparam
          in: query
          required: false
          schema:
            type: string
            format: date-time
      responses:
        "200":
          description: OK

Generation Details

java -jar openapi.jar generate -i openapi.yaml -g php-symfony -o out

Steps to reproduce

Plug the symfony bundle generated into a symfony app (following the steps in the auto-generated README). Then launch the symfony server and perform a query against this route, for instance:

  curl -i http://localhost:8000/my-route # this should be ok because the parameter is marked as non required
  # or also
  curl -i 'http://localhost:8000/my-route?myparam=2017-07-21T17:32:28Z'

Expected behavior: I receive a 200 response. Actual behavior: I receive a 400 response with content This value should be of type string`

Related issues/PRs

I've looked at https://github.com/OpenAPITools/openapi-generator/issues?q=is%3Aissue+symfony+date-time but those issues are not related to mine.

Suggest a fix

I think thos 3 changes may be needed to fix that issue:

Currently the generated Controller/DefaultController.php looks like that:

        // Read out all input parameter values into variables
        $myparam = $request->query->get('myparam');

        // Use the default value if no value was provided

        // Deserialize the input values that needs it
        try {
            $myparam = $this->deserialize($myparam, '\DateTime', 'string');
        } catch (SerializerRuntimeException $exception) {
            return $this->createBadRequestResponse($exception->getMessage());
        }

        // Validate the input values
        $asserts = [];
        $asserts[] = new Assert\DateTime();
        $response = $this->validate($myparam, $asserts);
        if ($response instanceof Response) {
            return $response;
        }

Here we see that the validation occurs after the deserialization. That explains the issue observed since the validation expects $myparam to be a string but it was already deserialized to DateTime. So I think the validation part should go before the deserialization, so that $myparam would still be a string at the moment where it is checked.

In the snippet above we see that the generated code relies on Symfony's Symfony\Component\Validator\DateTime to perform the assertion, however that class checks against the format Y-m-d H:i:s though open api specification considers that date-time should conform to RFC 3339 which would be for instance 2017-07-21T17:32:28Z. So I think this check should be adapted as well (not sure by what it should be replaced though)
The generated file service/JmsSerializer.php has a method deserializeString which returns new DateTime($data) for parameter of type date-time. But since new DateTime(null) represents "now" it means that if the parameter is not provided by the query (which should be ok since I marked it has non required) then the deserialization would return "now" instead of null. (perhaps this handling of null $data should also be applied to other format of strings? I don't know)