DATACMNS-783 - DefaultTypeMapper now specializes raw generic types.

If the type lookup from the store source returns a raw generic type (e.g. resolving the value of a generic property against a value of that generic type - i.e. not a more concrete type binding the generic information) in the context of a generic property, we previously did not apply the generics information of the contextual instance to that very raw type.

We now expose a TypeInformation.specialize(ClassTypeInformation) which applies the current generics context to the given raw type and basically creates a synthetic parameterized TypeInformation instance.

DefaultTypeMapper applies this specialization by default now with ClassTypeInformation simply returning the given type as is so that we don't create any resolution overhead in case no generics are involved in the first place.

src/main/java/org/springframework/data/convert/DefaultTypeMapper.java

@@ -147,10 +147,16 @@ public class DefaultTypeMapper<S> implements TypeMapper<S> {
 
 		Class<T> rawType = basicType == null ? null : basicType.getType();
 
-		boolean isMoreConcreteCustomType = rawType == null ? true : rawType.isAssignableFrom(documentsTargetType)
-				&& !rawType.equals(documentsTargetType);
-		return isMoreConcreteCustomType ? (TypeInformation<? extends T>) ClassTypeInformation.from(documentsTargetType)
-				: basicType;
+		boolean isMoreConcreteCustomType = rawType == null ? true
+				: rawType.isAssignableFrom(documentsTargetType) && !rawType.equals(documentsTargetType);
+
+		if (!isMoreConcreteCustomType) {
+			return basicType;
+		}
+
+		ClassTypeInformation<?> targetType = ClassTypeInformation.from(documentsTargetType);
+
+		return (TypeInformation<? extends T>) (basicType != null ? basicType.specialize(targetType) : targetType);
 	}
 
 	/**

src/main/java/org/springframework/data/util/ClassTypeInformation.java

@@ -167,6 +167,15 @@ public class ClassTypeInformation<S> extends TypeDiscoverer<S> {
 		return getType().isAssignableFrom(target.getType());
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.util.TypeDiscoverer#specialize(org.springframework.data.util.ClassTypeInformation)
+	 */
+	@Override
+	public TypeInformation<?> specialize(ClassTypeInformation<?> type) {
+		return type;
+	}
+
 	/* 
 	 * (non-Javadoc)
 	 * @see java.lang.Object#toString()

src/main/java/org/springframework/data/util/TypeDiscoverer.java

@@ -493,6 +493,20 @@ class TypeDiscoverer<S> implements TypeInformation<S> {
 		return target.getSuperTypeInformation(getType()).equals(this);
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.util.TypeInformation#specialize(org.springframework.data.util.ClassTypeInformation)
+	 */
+	@Override
+	public TypeInformation<?> specialize(ClassTypeInformation<?> type) {
+
+		Assert.isTrue(getType().isAssignableFrom(type.getType()));
+
+		List<TypeInformation<?>> arguments = getTypeArguments();
+
+		return arguments.isEmpty() ? type : createInfo(new SyntheticParamterizedType(type, arguments));
+	}
+
 	private TypeInformation<?> getTypeArgument(Class<?> bound, int index) {
 
 		Class<?>[] arguments = GenericTypeResolver.resolveTypeArguments(getType(), bound);
@@ -537,4 +551,63 @@ class TypeDiscoverer<S> implements TypeInformation<S> {
 	public int hashCode() {
 		return hashCode;
 	}
+
+	/**
+	 * A synthetic {@link ParameterizedType}.
+	 *
+	 * @author Oliver Gierke
+	 * @since 1.11
+	 */
+	private static class SyntheticParamterizedType implements ParameterizedType {
+
+		private final ClassTypeInformation<?> typeInformation;
+		private final List<TypeInformation<?>> typeParameters;
+
+		/**
+		 * @param typeInformation must not be {@literal null}.
+		 * @param typeParameters must not be {@literal null}.
+		 */
+		public SyntheticParamterizedType(ClassTypeInformation<?> typeInformation, List<TypeInformation<?>> typeParameters) {
+
+			Assert.notNull(typeInformation, "Type must not be null!");
+			Assert.notNull(typeParameters, "Type parameters must not be null!");
+
+			this.typeInformation = typeInformation;
+			this.typeParameters = typeParameters;
+		}
+
+		/*
+		 * (non-Javadoc)
+		 * @see java.lang.reflect.ParameterizedType#getRawType()
+		 */
+		@Override
+		public Type getRawType() {
+			return typeInformation.getType();
+		}
+
+		/*
+		 * (non-Javadoc)
+		 * @see java.lang.reflect.ParameterizedType#getOwnerType()
+		 */
+		@Override
+		public Type getOwnerType() {
+			return null;
+		}
+
+		/*
+		 * (non-Javadoc)
+		 * @see java.lang.reflect.ParameterizedType#getActualTypeArguments()
+		 */
+		@Override
+		public Type[] getActualTypeArguments() {
+
+			Type[] result = new Type[typeParameters.size()];
+
+			for (int i = 0; i < typeParameters.size(); i++) {
+				result[i] = typeParameters.get(0).getType();
+			}
+
+			return result;
+		}
+	}
 }

src/main/java/org/springframework/data/util/TypeInformation.java

@@ -140,4 +140,14 @@ public interface TypeInformation<S> {
 	 * @return
 	 */
 	List<TypeInformation<?>> getTypeArguments();
+
+	/**
+	 * Specializes the given (raw) {@link ClassTypeInformation} using the context of the current potentially parameterized
+	 * type, basically turning the given raw type into a parameterized one. Will return the given type as is if no
+	 * generics are involved.
+	 * 
+	 * @param type must not be {@literal null}.
+	 * @return will never be {@literal null}.
+	 */
+	TypeInformation<?> specialize(ClassTypeInformation<?> type);
 }