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Fix type parameters not being passed to fallback property codec #1765

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For some reason, type parameters weren't passed to fallback property codec, which caused an exception when trying to access them. Now, this issue is fixed.

@GliczDev GliczDev requested a review from a team as a code owner July 11, 2025 00:59
@GliczDev GliczDev requested review from NathanQingyangXu and removed request for a team July 11, 2025 00:59
@NathanQingyangXu
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@rozza , I am not sure about the validity of the code changes proposed. For one thing, it breaks 6 unit testing cases; secondly it seems FallbackPropertyCodecProvider opted for calling CodecRegistry#get(Type) intentionally, for the reason that the other get(Type, List<Type>() might not be overridden, thus defeating the purpose of fallback as the last resort.
How do you think?

@rozza
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rozza commented Jul 21, 2025

@GliczDev looks like this PR needs some tests and as @NathanQingyangXu mentioned this does appear to break some existing test cases.

To run the bson tests and checks run ./gradlew bson:check from the shell.

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I added a couple of requested changes - to support java 8+ and to ensure that types are only provided if the list is not empty.

The LookupCountingCodecRegistry implementation in tests will need to implement <T> Codec<T> get(Class<T> clazz, List<Type> typeArguments) inorder not to throw an exception.

eg:

@Override
public <T> Codec<T> get(final Class<T> clazz, final List<Type> typeArguments) {
        incrementCount(clazz);
        for (CodecProvider provider : codecProviders) {
            Codec<T> codec = provider.get(clazz, typeArguments, this);
            if (codec != null) {
                return codec;
            }
        }
        return null;
}

It would also be good to add a regression test where this code path is used.

@@ -19,6 +19,8 @@
import org.bson.codecs.Codec;
import org.bson.codecs.configuration.CodecRegistry;

import java.lang.reflect.Type;
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Suggested change
import java.lang.reflect.Type;
import java.lang.reflect.Type;
import java.util.List;
import java.util.stream.Collectors;

@@ -35,6 +37,6 @@ public <S> Codec<S> get(final TypeWithTypeParameters<S> type, final PropertyCode
if (clazz == pojoCodec.getEncoderClass()) {
return (Codec<S>) pojoCodec;
}
return codecRegistry.get(type.getType());
return codecRegistry.get(type.getType(), type.getTypeParameters().stream().<Type>map(TypeWithTypeParameters::getType).toList());
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Suggested change
return codecRegistry.get(type.getType(), type.getTypeParameters().stream().<Type>map(TypeWithTypeParameters::getType).toList());
List<Type> types = type.getTypeParameters().stream().<Type>map(TypeWithTypeParameters::getType).collect(Collectors.toList());
if (!types.isEmpty()) {
return codecRegistry.get(type.getType(), types);
}
return codecRegistry.get(type.getType());

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3 participants