fix: Return root when parts of a query with deferred fragment

NEXT_CHANGELOG.md

@@ -120,6 +120,31 @@ in a previous payload.
 
 By [@Geal](https://github.com/geal) in https://github.com/apollographql/router/pull/2184
 
+### Return root `__typename` when parts of a query with deferred fragment ([Issue #1677](https://github.com/apollographql/router/issues/1677))
+
+With this query:
+
+```graphql
+{
+  __typename
+  fast
+  ...deferedFragment @defer
+}
+
+fragment deferedFragment on Query {
+  slow
+}
+```
+
+You will received first response chunk:
+
+```json
+{"data":{"__typename": "Query", "fast":0},"hasNext":true}
+```
+
+By [@bnjjj](https://github.com/bnjjj) in https://github.com/apollographql/router/pull/2188
+
+
 ### wait for opentelemetry tracer provider to shutdown ([PR #2191](https://github.com/apollographql/router/pull/2191))
 
 When we drop Telemetry we spawn a thread to perform the global opentelemetry trace provider shutdown. The documentation of this function indicates that "This will invoke the shutdown method on all span processors. span processors should export remaining spans before return". We should give that process some time to complete (5 seconds currently) before returning from the `drop`. This will provide more opportunity for spans to be exported.

apollo-router/src/services/snapshots/apollo_router__services__supergraph_service__tests__root_typename_with_defer-2.snap

@@ -0,0 +1,42 @@
+---
+source: apollo-router/src/services/supergraph_service.rs
+expression: stream.next_response().await.unwrap()
+---
+{
+  "hasNext": false,
+  "incremental": [
+    {
+      "data": {
+        "name": null
+      },
+      "path": [
+        "currentUser",
+        "activeOrganization",
+        "suborga",
+        0
+      ]
+    },
+    {
+      "data": {
+        "name": "A"
+      },
+      "path": [
+        "currentUser",
+        "activeOrganization",
+        "suborga",
+        1
+      ]
+    },
+    {
+      "data": {
+        "name": null
+      },
+      "path": [
+        "currentUser",
+        "activeOrganization",
+        "suborga",
+        2
+      ]
+    }
+  ]
+}

apollo-router/src/services/snapshots/apollo_router__services__supergraph_service__tests__root_typename_with_defer.snap

@@ -0,0 +1,26 @@
+---
+source: apollo-router/src/services/supergraph_service.rs
+expression: res
+---
+{
+  "data": {
+    "currentUser": {
+      "activeOrganization": {
+        "id": "0",
+        "suborga": [
+          {
+            "id": "1"
+          },
+          {
+            "id": "2"
+          },
+          {
+            "id": "3"
+          }
+        ]
+      }
+    },
+    "__typename": "Query"
+  },
+  "hasNext": true
+}

apollo-router/src/services/supergraph_service.rs

@@ -779,6 +779,82 @@ mod tests {
         insta::assert_json_snapshot!(stream.next_response().await.unwrap());
     }
 
+    #[tokio::test]
+    async fn root_typename_with_defer() {
+        let subgraphs = MockedSubgraphs([
+        ("user", MockSubgraph::builder().with_json(
+                serde_json::json!{{"query":"{currentUser{activeOrganization{__typename id}}}"}},
+                serde_json::json!{{"data": {"currentUser": { "activeOrganization": { "__typename": "Organization", "id": "0" } }}}}
+            ).build()),
+        ("orga", MockSubgraph::builder().with_json(
+            serde_json::json!{{
+                "query":"query($representations:[_Any!]!){_entities(representations:$representations){...on Organization{suborga{__typename id}}}}",
+                "variables": {
+                    "representations":[{"__typename": "Organization", "id":"0"}]
+                }
+            }},
+            serde_json::json!{{
+                "data": {
+                    "_entities": [{ "suborga": [
+                    { "__typename": "Organization", "id": "1"},
+                    { "__typename": "Organization", "id": "2"},
+                    { "__typename": "Organization", "id": "3"},
+                    ] }]
+                },
+                }}
+        )
+        .with_json(
+            serde_json::json!{{
+                "query":"query($representations:[_Any!]!){_entities(representations:$representations){...on Organization{name}}}",
+                "variables": {
+                    "representations":[
+                        {"__typename": "Organization", "id":"1"},
+                        {"__typename": "Organization", "id":"2"},
+                        {"__typename": "Organization", "id":"3"}
+
+                        ]
+                }
+            }},
+            serde_json::json!{{
+                "data": {
+                    "_entities": [
+                    { "__typename": "Organization", "id": "1"},
+                    { "__typename": "Organization", "id": "2", "name": "A"},
+                    { "__typename": "Organization", "id": "3"},
+                    ]
+                }
+                }}
+        ).build())
+    ].into_iter().collect());
+
+        let service = TestHarness::builder()
+            .configuration_json(serde_json::json!({"include_subgraph_errors": { "all": true } }))
+            .unwrap()
+            .schema(SCHEMA)
+            .extra_plugin(subgraphs)
+            .build()
+            .await
+            .unwrap();
+
+        let request = supergraph::Request::fake_builder()
+            .header("Accept", "multipart/mixed; deferSpec=20220824")
+            .query(
+                "query { __typename currentUser { activeOrganization { id  suborga { id ...@defer { name } } } } }",
+            )
+            .build()
+            .unwrap();
+
+        let mut stream = service.oneshot(request).await.unwrap();
+        let res = stream.next_response().await.unwrap();
+        assert_eq!(
+            res.data.as_ref().unwrap().get("__typename"),
+            Some(&serde_json_bytes::Value::String("Query".into()))
+        );
+        insta::assert_json_snapshot!(res);
+
+        insta::assert_json_snapshot!(stream.next_response().await.unwrap());
+    }
+
     #[tokio::test]
     async fn query_reconstruction() {
         let schema = r#"schema

apollo-router/src/spec/query.rs

@@ -211,9 +211,8 @@ impl Query {
         schema: &Schema,
         configuration: &Configuration,
     ) -> Result<Self, SpecError> {
-        let string = query.into();
-
-        let parser = apollo_parser::Parser::new(string.as_str())
+        let query = query.into();
+        let parser = apollo_parser::Parser::new(query.as_str())
             .recursion_limit(configuration.server.experimental_parser_recursion_limit);
         let tree = parser.parse();
 
@@ -248,7 +247,7 @@ impl Query {
             .collect::<Result<Vec<_>, SpecError>>()?;
 
         Ok(Query {
-            string,
+            string: query,
             fragments,
             operations,
             subselections: HashMap::new(),
@@ -837,6 +836,17 @@ impl Query {
                 }
             }
         }
+        // Detect if root __typename is asked in the original query (the qp doesn't put root __typename in subselections)
+        // cf https://github.com/apollographql/router/issues/1677
+        let operation_kind_if_root_typename = self.operations.get(0).and_then(|op| {
+            op.selection_set
+                .iter()
+                .any(|f| f.is_typename_field())
+                .then(|| *op.kind())
+        });
+        if let Some(operation_kind) = operation_kind_if_root_typename {
+            output.insert(TYPENAME, operation_kind.as_str().into());
+        }
 
         Ok(())
     }
@@ -1066,7 +1076,7 @@ impl Operation {
             && self
                 .selection_set
                 .get(0)
-                .map(|s| matches!(s, Selection::Field {name, ..} if name.as_str() == TYPENAME))
+                .map(|s| s.is_typename_field())
                 .unwrap_or_default()
     }
 

apollo-router/src/spec/selection.rs

@@ -314,6 +314,10 @@ impl Selection {
 
         Ok(selection)
     }
+
+    pub(crate) fn is_typename_field(&self) -> bool {
+        matches!(self, Selection::Field {name, ..} if name.as_str() == TYPENAME)
+    }
 }
 
 pub(crate) fn parse_skip(directive: &ast::Directive) -> Option<Skip> {