WebTestClient leaks when ParameterizedTypeReference is used

[MFAshby]

WebTestClient has a special case when a Void response is expected. Method WebTestClient.ResponseSpec#returnResult(java.lang.Class<T>) has this documentation comment:

Note that when {@code Void.class} is passed in, the response body is consumed and released.

The same special case logic is not applied to the overloaded version of this method: WebTestClient.ResponseSpec#returnResult(ParameterizedTypeReference<T>). This is a bit unexpected; and caused a memory leak in my tests when I swapped a Class parameter for a ParameterizedTypeReference parameter. The following sample code shows the problem (additional GC is forced to make the leak happen faster; netty's leak detection happens on GC):

import org.springframework.core.ParameterizedTypeReference;
import org.springframework.http.client.reactive.ReactorClientHttpConnector;
import org.springframework.test.web.reactive.server.WebTestClient;
import reactor.netty.http.client.HttpClient;

class Scratch {
    public static void main(String[] args) throws Exception {
        var client = WebTestClient.bindToServer(new ReactorClientHttpConnector(HttpClient.create()))
                .build();
        var b = client.get().uri("http://localhost:8000");
        long count = 0;
        while(true) {
            count += 1;
            if (count % 10000 == 0) {
                System.out.printf("Done %d requests forcing a G\n", count);
                System.gc();
            }
            b.exchange()
                    .expectStatus().isEqualTo(200)
                    //.returnResult(Void.class);                                       // <-- doesn't leak
                    .returnResult(ParameterizedTypeReference.forType(Void.class)); // <-- leaks
        }
    }
}

The workaround is to use the Class signature, or consume the response body some other way using e.g. by specifying .consumeWith(...).