feat: handle null coercion in cynic-parser-deser (#1100)

cynic-parser-deser/src/deserialize.rs

@@ -152,7 +152,17 @@ where
     fn deserialize(input: DeserValue<'a>) -> Result<Self, Error> {
         match input {
             DeserValue::List(list) => list.items().map(T::deserialize).collect(),
-            other => Err(Error::unexpected_type(ValueType::List, other)),
+            other => {
+                if !other.is_null() {
+                    // List coercion
+                    //
+                    // I am not 100% sure this is right but lets see...
+                    if let Ok(inner) = T::deserialize(other) {
+                        return Ok(vec![inner]);
+                    }
+                }
+                Err(Error::unexpected_type(ValueType::List, other))
+            }
         }
     }
 }

cynic-parser-deser/tests/deser.rs

@@ -93,6 +93,37 @@ fn test_rename_rule() {
     assert_eq!(deser::<RenameRule>("@id(fooBar: 1)").unwrap().foo_bar, 1);
 }
 
+#[derive(ValueDeserialize, PartialEq, Debug)]
+struct ListCoercion {
+    ints: Vec<u32>,
+    strings: Vec<String>,
+}
+
+#[test]
+fn test_list_coercion() {
+    assert_eq!(
+        deser::<ListCoercion>("@id(ints: 1, strings: \"hello\")").unwrap(),
+        ListCoercion {
+            ints: vec![1],
+            strings: vec!["hello".into()]
+        }
+    );
+
+    assert_eq!(
+        deser::<ListCoercion>("@id(ints: \"hello\", strings: 1)")
+            .unwrap_err()
+            .to_string(),
+        "found a String where we expected a List"
+    );
+
+    assert_eq!(
+        deser::<ListCoercion>("@id(ints: null, strings: 1)")
+            .unwrap_err()
+            .to_string(),
+        "found a Null where we expected a List"
+    );
+}
+
 fn deser<T>(input: &str) -> Result<T, cynic_parser_deser::Error>
 where
     T: ValueDeserializeOwned,