Use target collection type for binding

This commit ensures that the `GraphQlArgumentBinder` is using the target collection type (on the type we're binding to) to create a new collection instance when using constructor binding. Fixes gh-485

Author: bclozel

spring-graphql/src/main/java/org/springframework/graphql/data/GraphQlArgumentBinder.java

@@ -209,7 +209,7 @@ private <T> Collection<T> createCollection(
 return Collections.emptyList();
 }
 
-Collection<T> collection = CollectionFactory.createApproximateCollection(rawCollection, rawCollection.size());
+Collection<T> collection = CollectionFactory.createCollection(collectionType.getRawClass(), elementClass, rawCollection.size());
 int i = 0;
 for (Object rawValue : rawCollection) {
 segments.push("[" + i++ + "]");

spring-graphql/src/test/java/org/springframework/graphql/data/GraphQlArgumentBinderTests.java

@@ -19,8 +19,11 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
@@ -268,6 +271,16 @@ void shouldHaveHigherDefaultAutoGrowLimit() throws Exception {
 assertThat(((ItemListHolder) result).getItems()).hasSize(260);
 }
 
+@Test
+void shouldUseTargetCollectionType() throws Exception {
+String items = IntStream.range(0, 5).mapToObj(value -> "{\"name\":\"test" + value + "\"}").collect(Collectors.joining(","));
+Object result = this.binder.bind(
+environment("{\"key\":{\"items\":[" + items + "]}}"), "key",
+ResolvableType.forClass(ItemSetHolder.class));
+assertThat(result).isNotNull().isInstanceOf(ItemSetHolder.class);
+assertThat(((ItemSetHolder) result).getItems()).hasSize(5);
+}
+
 
 @SuppressWarnings("unchecked")
 private DataFetchingEnvironment environment(String jsonPayload) throws JsonProcessingException {
@@ -401,6 +414,36 @@ public int getAge() {
 public void setAge(int age) {
 this.age = age;
 }
+
+@Override
+public boolean equals(Object o) {
+if (this == o) return true;
+if (o == null || getClass() != o.getClass()) return false;
+Item item = (Item) o;
+return name.equals(item.name);
+}
+
+@Override
+public int hashCode() {
+return Objects.hash(name);
+}
+}
+
+static class ItemSetHolder {
+
+private Set<Item> items;
+
+public ItemSetHolder(Set<Item> items) {
+this.items = items;
+}
+
+public Set<Item> getItems() {
+return items;
+}
+
+public void setItems(Set<Item> items) {
+this.items = items;
+}
 }
 
 }