fix(discriminator): union nullable

src/core/ir/discriminator.rs

@@ -36,10 +36,14 @@ where
         if let Some(obj) = self.as_object_mut() {
             obj.insert_key(TYPENAME_FIELD, T::string(type_name.into()));
 
-            Ok(())
-        } else {
-            bail!("Expected object")
+            return Ok(());
         }
+
+        if self.is_null() {
+            return Ok(());
+        }
+
+        bail!("Value expected to be object")
     }
 }
 
@@ -70,6 +74,8 @@ pub struct Discriminator {
     /// Set of all fields that are part of types with
     /// the [FieldInfo] about their relations to types.
     fields_info: IndexMap<String, FieldInfo>,
+    /// The name of parent type
+    name: String,
 }
 
 impl std::fmt::Debug for Discriminator {
@@ -227,7 +233,7 @@ impl Discriminator {
                 .collect()
         };
 
-        let discriminator = Self { fields_info, types };
+        let discriminator = Self { fields_info, types, name: union_name.to_string() };
 
         tracing::debug!(
             "Generated discriminator for union type '{union_name}':\n{discriminator:?}",
@@ -238,7 +244,7 @@ impl Discriminator {
 
     pub fn resolve_type(&self, value: &Value) -> Result<&str> {
         let Value::Object(obj) = value else {
-            bail!("Value expected to be object");
+            return Ok(&self.name);
         };
 
         let mut possible_types = Repr::all_covered(self.types.len());
@@ -1228,17 +1234,15 @@ mod tests {
         assert_eq!(
             discriminator
                 .resolve_type(&Value::from_json(json!("string")).unwrap())
-                .unwrap_err()
-                .to_string(),
-            "Value expected to be object"
+                .unwrap(),
+            "Test"
         );
 
         assert_eq!(
             discriminator
                 .resolve_type(&Value::from_json(json!(25)).unwrap())
-                .unwrap_err()
-                .to_string(),
-            "Value expected to be object"
+                .unwrap(),
+            "Test"
         );
     }
 }

tests/core/snapshots/test-union-optional.md_0.snap

@@ -0,0 +1,15 @@
+---
+source: tests/core/spec.rs
+expression: response
+---
+{
+  "status": 200,
+  "headers": {
+    "content-type": "application/json"
+  },
+  "body": {
+    "data": {
+      "nodes": null
+    }
+  }
+}

tests/core/snapshots/test-union-optional.md_client.snap

@@ -0,0 +1,59 @@
+---
+source: tests/core/spec.rs
+expression: formatted
+---
+scalar Bytes
+
+scalar Date
+
+scalar DateTime
+
+scalar Email
+
+scalar Empty
+
+scalar Int128
+
+scalar Int16
+
+scalar Int32
+
+scalar Int64
+
+scalar Int8
+
+scalar JSON
+
+union Node = Page | User
+
+type Page {
+  id: ID!
+  slug: String!
+}
+
+scalar PhoneNumber
+
+type Query {
+  nodes: Node
+}
+
+scalar UInt128
+
+scalar UInt16
+
+scalar UInt32
+
+scalar UInt64
+
+scalar UInt8
+
+scalar Url
+
+type User {
+  id: ID!
+  username: String!
+}
+
+schema {
+  query: Query
+}

tests/core/snapshots/test-union-optional.md_merged.snap

@@ -0,0 +1,23 @@
+---
+source: tests/core/spec.rs
+expression: formatter
+---
+schema @server @upstream {
+  query: Query
+}
+
+union Node = Page | User
+
+type Page {
+  id: ID!
+  slug: String!
+}
+
+type Query {
+  nodes: Node @expr
+}
+
+type User {
+  id: ID!
+  username: String!
+}

tests/execution/test-union-optional.md

@@ -0,0 +1,43 @@
+# Test union optional
+
+```graphql @config
+schema @server {
+  query: Query
+}
+
+type Query {
+  nodes: Node @expr(body: null)
+}
+
+union Node = User | Page
+
+type User {
+  id: ID!
+  username: String!
+}
+
+type Page {
+  id: ID!
+  slug: String!
+}
+```
+
+```yml @test
+- method: POST
+  url: http://localhost:8080/graphql
+  body:
+    query: |
+      {
+        nodes {
+          __typename
+          ... on Page {
+            id
+            slug
+          }
+          ... on User {
+            id
+            username
+          }
+        }
+      }
+```