Fix serializing of JSON default values (#969)

* Fix serializing of JSON default values

* fix format of other code due to new nightly

src/types/json.rs

@@ -63,7 +63,7 @@ impl<T: DeserializeOwned + Serialize + Send + Sync> InputType for Json<T> {
     }
 
     fn to_value(&self) -> Value {
-        to_value(&self.0).unwrap_or_default()
+        Value::String(serde_json::to_string(&self.0).unwrap_or_default())
     }
 
     fn as_raw_value(&self) -> Option<&Self::RawValueType> {
@@ -120,7 +120,7 @@ impl InputType for serde_json::Value {
     }
 
     fn to_value(&self) -> Value {
-        to_value(&self).unwrap_or_default()
+        Value::String(self.to_string())
     }
 
     fn as_raw_value(&self) -> Option<&Self::RawValueType> {

tests/introspection.rs

@@ -1,4 +1,5 @@
 use async_graphql::*;
+use chrono::{NaiveDate, NaiveDateTime};
 use futures_util::stream::{self, Stream};
 
 #[derive(Clone, Debug)]
@@ -1378,3 +1379,135 @@ pub async fn test_introspection_only() {
     let res = schema.execute(query).await.into_result().unwrap().data;
     assert_eq!(res, res_json);
 }
+
+#[tokio::test]
+pub async fn test_introspection_default() {
+    #[derive(serde::Serialize, serde::Deserialize, Default)]
+    pub struct MyStruct {
+        a: i32,
+        b: i32,
+    }
+
+    #[derive(InputObject)]
+    pub struct DefaultInput {
+        #[graphql(default)]
+        pub str: String,
+        #[graphql(default_with = "NaiveDate::from_ymd(2016, 7, 8).and_hms(9, 10, 11)")]
+        pub date: NaiveDateTime,
+        // a required json with no default
+        pub json: serde_json::Value,
+        // basic default (JSON null)
+        #[graphql(default)]
+        pub json_def: serde_json::Value,
+        // complex default (JSON object)
+        #[graphql(default_with = "serde_json::Value::Object(Default::default())")]
+        pub json_def_obj: serde_json::Value,
+        #[graphql(default)]
+        pub json_def_struct: Json<MyStruct>,
+    }
+
+    struct LocalMutation;
+
+    #[Object]
+    #[allow(unreachable_code)]
+    impl LocalMutation {
+        async fn simple_mutation(&self, _input: DefaultInput) -> SimpleObject {
+            unimplemented!()
+        }
+    }
+
+    let schema = Schema::build(Query, LocalMutation, EmptySubscription)
+        .introspection_only()
+        .finish();
+
+    // Test whether introspection works.
+    let query = r#"
+        {
+            __type(name: "DefaultInput") {
+                name
+                kind
+                inputFields {
+                    name
+                    defaultValue
+                    type { kind ofType { kind name } }
+                }
+            }
+        }
+    "#;
+    let res_json = value!({
+        "__type": {
+            "name": "DefaultInput",
+            "kind": "INPUT_OBJECT",
+            "inputFields": [
+              {
+                "name": "str",
+                "defaultValue": "\"\"",
+                "type": {
+                  "kind": "NON_NULL",
+                  "ofType": {
+                      "kind": "SCALAR",
+                      "name": "String"
+                  },
+                },
+              },
+              {
+                "name": "date",
+                "defaultValue": "\"2016-07-08T09:10:11\"",
+                "type": {
+                  "kind": "NON_NULL",
+                  "ofType": {
+                      "kind": "SCALAR",
+                      "name": "NaiveDateTime"
+                  },
+                },
+              },
+              {
+                "name": "json",
+                "defaultValue": null,
+                "type": {
+                  "kind": "NON_NULL",
+                  "ofType": {
+                      "kind": "SCALAR",
+                      "name": "JSON"
+                  },
+                },
+              },
+              {
+                "name": "jsonDef",
+                "defaultValue": "\"null\"",
+                "type": {
+                  "kind": "NON_NULL",
+                  "ofType": {
+                      "kind": "SCALAR",
+                      "name": "JSON"
+                  },
+                },
+              },
+              {
+                "name": "jsonDefObj",
+                "defaultValue": "\"{}\"",
+                "type": {
+                  "kind": "NON_NULL",
+                  "ofType": {
+                      "kind": "SCALAR",
+                      "name": "JSON"
+                  },
+                },
+              },
+              {
+                "name": "jsonDefStruct",
+                "defaultValue": "\"{\\\"a\\\":0,\\\"b\\\":0}\"",
+                "type": {
+                  "kind": "NON_NULL",
+                  "ofType": {
+                      "kind": "SCALAR",
+                      "name": "JSON"
+                  },
+                },
+              },
+            ]
+        }
+    });
+    let res = schema.execute(query).await.into_result().unwrap().data;
+    assert_eq!(res, res_json);
+}