DATACMNS-1252 - Improved Vavr collection handling to convert between collection types.

If a query method now uses e.g. a Vavr Set as return type, we now also use a potential source List as input for the LinkedHashSet, even if that changes the characteristics (duplicate policy etc.) of the result. This is consistent with our general handling of collections as we're using a Spring ConversionService for collection mapping anyway.

In general the new conversion algorithm is driven by the expected target type first:

- i.v.c.Seq -> i.v.c.List
- i.v.c.Set -> i.v.c.LinkedHashSet
- i.v.c.Map -> i.v.c.LinkedHashMap

If none of the declared types is assignable we fall back to the previous algorithm choosing an implementation as close as possible to the original source value:

- j.u.List -> i.v.c.List
- j.u.Set  -> i.v.c.LinkedHashSet
- j.u.Map  -> i.v.c.LinkedHashMap

Removed some obsolete full qualifications of types.

src/main/java/org/springframework/data/repository/util/VavrCollections.java

@@ -116,18 +116,35 @@ class VavrCollections {
 			*/
 			@Nullable
 			@Override
-			public Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
+			public Object convert(@Nullable Object source, TypeDescriptor sourceDescriptor, TypeDescriptor targetDescriptor) {
+
+				Class<?> targetType = targetDescriptor.getType();
+
+				if (io.vavr.collection.Seq.class.isAssignableFrom(targetType)) {
+					return io.vavr.collection.List.ofAll((Iterable<?>) source);
+				}
+
+				if (io.vavr.collection.Set.class.isAssignableFrom(targetType)) {
+					return LinkedHashSet.ofAll((Iterable<?>) source);
+				}
+
+				if (io.vavr.collection.Map.class.isAssignableFrom(targetType)) {
+					return LinkedHashMap.ofAll((Map<?, ?>) source);
+				}
+
+				// No dedicated type asked for, probably Traversable.
+				// Try to stay as close to the source value.
 
 				if (source instanceof List) {
 					return io.vavr.collection.List.ofAll((Iterable<?>) source);
 				}
 
-				if (source instanceof java.util.Set) {
+				if (source instanceof Set) {
 					return LinkedHashSet.ofAll((Iterable<?>) source);
 				}
 
-				if (source instanceof java.util.Map) {
-					return LinkedHashMap.ofAll((java.util.Map<?, ?>) source);
+				if (source instanceof Map) {
+					return LinkedHashMap.ofAll((Map<?, ?>) source);
 				}
 
 				return source;

src/test/java/org/springframework/data/repository/util/QueryExecutionConvertersUnitTests.java

@@ -338,4 +338,13 @@ public class QueryExecutionConvertersUnitTests {
 		Set<Class<?>> allowedPageableTypes = QueryExecutionConverters.getAllowedPageableTypes();
 		assertThat(allowedPageableTypes).contains(io.vavr.collection.Seq.class);
 	}
+
+	@Test // DATAJPA-1258
+	public void convertsJavaListsToVavrSet() {
+
+		List<String> source = Collections.singletonList("foo");
+
+		assertThat(conversionService.convert(source, io.vavr.collection.Set.class)) //
+				.isInstanceOf(io.vavr.collection.Set.class);
+	}
 }