Spring GenericTypeResolver does not resolve nested generics - causes issues with Jackson & Spring MVC

This affects spring 6.1.1

The following test passes on 6.0.14 but fails on 6.1.1

import static org.assertj.core.api.Assertions.assertThat;
import static org.springframework.util.ReflectionUtils.findMethod;

import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Map;

import org.junit.jupiter.api.Test;
import org.springframework.core.GenericTypeResolver;
import org.springframework.core.MethodParameter;
import org.springframework.core.ParameterizedTypeReference;

public class GenericConverterTypeTest {

    @Test
    public void foo() {
        Method method = findMethod(Bar.class, "accept", (Class<?>[])null);
        MethodParameter intMessageMethodParam = new MethodParameter(method, 0);
        Type resolveType = GenericTypeResolver.resolveType(intMessageMethodParam.getGenericParameterType(), Bar.class);
        ParameterizedTypeReference<List<Map<String, Integer>>> reference = new ParameterizedTypeReference<List<Map<String, Integer>>>() {
        };
        assertThat(resolveType).isEqualTo(reference.getType());
    }

    public class Bar {
        public void accept(List<Map<String, Integer>> input) {

        }
    }
}

Failure message:

org.opentest4j.AssertionFailedError: 
expected: java.util.List<java.util.Map<java.lang.String, java.lang.Integer>>
 but was: java.util.List<java.util.Map>
    at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
    at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
    at app.hs.platform.server.GenericConverterTypeTest.foo(GenericConverterTypeTest.java:25)
    at java.base/java.lang.reflect.Method.invoke(Method.java:580)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)

I believe this was caused by https://github.com/spring-projects/spring-framework/commit/f075120675028e396a24deb97e3a32327bbaa479

This causes nested generic deserialisation to fail from jackson due to the use of GenericTypeResolver in org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.getJavaType(Type, Class<?>)

Comment From: quaff

It's duplicate of https://github.com/spring-projects/spring-framework/issues/24963 It should be fixed by https://github.com/spring-projects/spring-framework/pull/30079

Comment From: snicoll

Thanks @quaff, I also assumed your work would fix this. However I don't think this is a duplicate as this used to work in 6.0.x and I'd like to understand why it broke.

Comment From: harmonic-ben

Hadn't really had time to look at this properly hence the poorly formatted test and believe line but it seems GenericTypeResolver.resolveType purpose is for using the context class to fill in additional type information. In this case it seems the type arrives will all type information supplied and just needs to be passed back. i.e. https://github.com/spring-projects/spring-framework/pull/30079 seems to be doing a lot of work for a type that needs no enhancement.

Comment From: sdeleuze

That's a bit embarrassing, but it looks like I shipped involuntarily a commit related to #22313 which is still opened while working on another issue, sorry about that. When I worked deeper on that issue, I found that by design Kotlin reflection is required to solve the Kotlin issue, and I was afraid of potential regressions on Java side, and chose to document the behavior via #31370. As a consequence, I plan to revert f075120675028e396a24deb97e3a32327bbaa479.