`@EmptySource` not working with `ArgumentConverter` accepting its supported types

[scordio]

Currently, EmptyArgumentsProvider directly checks the type of the first declared parameter and does not know of potential converters declared for that parameter, so it will throw a PreconditionViolationException if the declared type doesn't match the expectations.

Looking ahead to when #4219 is integrated, a globally-configured converter might even make the situation more complicated.

Steps to reproduce

Given an ArgumentConverter accepting strings, like:

class StringToBytesConverter extends TypedArgumentConverter<String, byte[]> {

    protected StringToBytesConverter() {
        super(String.class, byte[].class);
    }

    @Override
    protected byte[] convert(String source) {
        return source.getBytes();
    }

}

the following test passes:

@ParameterizedTest
@FieldSource
void fieldSourceTest(@ConvertWith(StringToBytesConverter.class) byte[] bytes) {
    assertEquals(0, bytes.length);
}

static List<String> fieldSourceTest = List.of("");

but the following test does not:

@ParameterizedTest
@EmptySource
void emptySourceTest(@ConvertWith(StringToBytesConverter.class) byte[] bytes) {
    assertEquals(0, bytes.length);
}

failing with:

org.junit.jupiter.api.extension.ParameterResolutionException: Error converting parameter at index 0: MyConverter cannot convert objects of type [[B]. Only source objects of type [java.lang.String] are supported.

Similar reproducers can be composed for all other @EmptySource supported types, like Collection, Map, etc.

Context

• Used versions (Jupiter/Vintage/Platform): 5.13.4
• Build Tool/IDE: Maven/IntelliJ IDEA

Deliverables

• @EmptySource provides the empty argument accepted by the available converter

or

• @EmptySource Javadoc explicitly mentions its incompatibility with argument conversion

[scordio]

The more I think about it, the more I feel like a solution might require a level of complexity that doesn't justify the gain...

I mentioned as a deliverable:

@EmptySource provides the empty argument accepted by the available converter

What if the available converter accepts more than one type supported by @EmptySource, e.g., both Collection and Map? Which empty instance should @EmptySource provide?