feat: add enableFederation flag to server

generated/.tailcallrc.graphql

@@ -281,6 +281,11 @@ directive @server(
   introducing latency and complicating debugging. Use judiciously. @default `false`.
   """
   batchRequests: Boolean
+  """
+  `enableFederation` enables functionality to Tailcall server to act as a federation 
+  subgraph.
+  """
+  enableFederation: Boolean
   enableJIT: Boolean
   """
   `globalResponseTimeout` sets the maximum query duration before termination, acting 

generated/.tailcallrc.schema.json

@@ -1046,6 +1046,23 @@
             "null"
           ]
         },
+<<<<<<< HEAD
+        "dedupe": {
+          "description": "Enables deduplication of IO operations to enhance performance.\n\nThis flag prevents duplicate IO requests from being executed concurrently, reducing resource load. Caution: May lead to issues with APIs that expect unique results for identical inputs, such as nonce-based APIs.",
+          "type": [
+            "boolean",
+            "null"
+          ]
+        },
+        "enableFederation": {
+          "description": "`enableFederation` enables functionality to Tailcall server to act as a federation subgraph.",
+          "type": [
+            "boolean",
+            "null"
+          ]
+        },
+=======
+>>>>>>> main
         "enableJIT": {
           "type": [
             "boolean",

src/core/config/server.rs

@@ -69,6 +69,11 @@ pub struct Server {
     /// and operations. @default `true`.
     pub introspection: Option<bool>,
 
+    /// `enableFederation` enables functionality to Tailcall server to act
+    /// as a federation subgraph.
+    #[serde(default, skip_serializing_if = "is_default")]
+    pub enable_federation: Option<bool>,
+
     #[serde(default, skip_serializing_if = "is_default")]
     /// `pipelineFlush` allows to control flushing behavior of the server
     /// pipeline.

src/core/config/transformer/subgraph.rs

@@ -34,6 +34,13 @@ impl Transform for Subgraph {
     type Error = String;
 
     fn transform(&self, mut config: Self::Value) -> Valid<Self::Value, Self::Error> {
+        let enable_federation = config.server.enable_federation;
+
+        if matches!(enable_federation, Some(false)) {
+            // if federation is disabled explicitly don't process the config
+            return Valid::succeed(config);
+        }
+
         let mut resolver_by_type = BTreeMap::new();
 
         let valid = Valid::from_iter(config.types.iter_mut(), |(type_name, ty)| {
@@ -55,26 +62,12 @@ impl Transform for Subgraph {
             return valid.map_to(config);
         }
 
-        if resolver_by_type.is_empty() {
+        if resolver_by_type.is_empty() && enable_federation.is_none() {
+            // if federation is not explicitly enabled and there is no entity
+            // resolvers return config as is
             return Valid::succeed(config);
         }
 
-        let entity_union = Union {
-            types: resolver_by_type.keys().cloned().collect(),
-            ..Default::default()
-        };
-
-        let entity_resolver = config::EntityResolver { resolver_by_type };
-
-        // union that wraps any possible types for entities
-        config
-            .unions
-            .insert(UNION_ENTITIES_NAME.to_owned(), entity_union);
-        // any scalar for argument `representations`
-        config
-            .types
-            .insert(ENTITIES_TYPE_NAME.to_owned(), config::Type::default());
-
         let service_field = Field { type_of: "String".to_string().into(), ..Default::default() };
 
         let service_type = config::Type {
@@ -87,38 +80,15 @@ impl Transform for Subgraph {
             .types
             .insert(SERVICE_TYPE_NAME.to_owned(), service_type);
 
-        let query_type = match config.schema.query.as_ref() {
+        let query_type_name = match config.schema.query.as_ref() {
             Some(name) => name,
             None => {
                 config.schema.query = Some("Query".to_string());
                 "Query"
             }
         };
 
-        let query_type = config.types.entry(query_type.to_owned()).or_default();
-
-        let arg = Arg {
-            type_of: Type::from(ENTITIES_TYPE_NAME.to_string())
-                .into_required()
-                .into_list()
-                .into_required(),
-            ..Default::default()
-        };
-
-        query_type.fields.insert(
-            ENTITIES_FIELD_NAME.to_string(),
-            Field {
-                type_of: Type::from(UNION_ENTITIES_NAME.to_owned())
-                    .into_list()
-                    .into_required(),
-                args: [(ENTITIES_ARG_NAME.to_owned(), arg)].into_iter().collect(),
-                doc: Some("Apollo federation Query._entities resolver".to_string()),
-                resolver: Some(Resolver::ApolloFederation(
-                    ApolloFederation::EntityResolver(entity_resolver),
-                )),
-                ..Default::default()
-            },
-        );
+        let query_type = config.types.entry(query_type_name.to_owned()).or_default();
 
         query_type.fields.insert(
             SERVICE_FIELD_NAME.to_string(),
@@ -130,6 +100,49 @@ impl Transform for Subgraph {
             },
         );
 
+        if !resolver_by_type.is_empty() {
+            let entity_union = Union {
+                types: resolver_by_type.keys().cloned().collect(),
+                ..Default::default()
+            };
+
+            let entity_resolver = config::EntityResolver { resolver_by_type };
+
+            // union that wraps any possible types for entities
+            config
+                .unions
+                .insert(UNION_ENTITIES_NAME.to_owned(), entity_union);
+            // any scalar for argument `representations`
+            config
+                .types
+                .insert(ENTITIES_TYPE_NAME.to_owned(), config::Type::default());
+
+            let query_type = config.types.entry(query_type_name.to_owned()).or_default();
+
+            let arg = Arg {
+                type_of: Type::from(ENTITIES_TYPE_NAME.to_string())
+                    .into_required()
+                    .into_list()
+                    .into_required(),
+                ..Default::default()
+            };
+
+            query_type.fields.insert(
+                ENTITIES_FIELD_NAME.to_string(),
+                Field {
+                    type_of: Type::from(UNION_ENTITIES_NAME.to_owned())
+                        .into_list()
+                        .into_required(),
+                    args: [(ENTITIES_ARG_NAME.to_owned(), arg)].into_iter().collect(),
+                    doc: Some("Apollo federation Query._entities resolver".to_string()),
+                    resolver: Some(Resolver::ApolloFederation(
+                        ApolloFederation::EntityResolver(entity_resolver),
+                    )),
+                    ..Default::default()
+                },
+            );
+        }
+
         Valid::succeed(config)
     }
 }

tests/core/snapshots/federation-subgraph-force-disabled.md_0.snap

@@ -0,0 +1,13 @@
+---
+source: tests/core/spec.rs
+expression: response
+---
+{
+  "status": 200,
+  "headers": {
+    "content-type": "application/json"
+  },
+  "body": {
+    "data": {}
+  }
+}

tests/core/snapshots/federation-subgraph-force-disabled.md_1.snap

@@ -0,0 +1,13 @@
+---
+source: tests/core/spec.rs
+expression: response
+---
+{
+  "status": 200,
+  "headers": {
+    "content-type": "application/json"
+  },
+  "body": {
+    "data": {}
+  }
+}

tests/core/snapshots/federation-subgraph-force-disabled.md_client.snap

@@ -0,0 +1,52 @@
+---
+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
+
+scalar PhoneNumber
+
+type Query {
+  user(id: Int!): User
+}
+
+scalar UInt128
+
+scalar UInt16
+
+scalar UInt32
+
+scalar UInt64
+
+scalar UInt8
+
+scalar Url
+
+type User {
+  id: Int!
+  name: String!
+}
+
+schema {
+  query: Query
+}

tests/core/snapshots/federation-subgraph-force-disabled.md_merged.snap

@@ -0,0 +1,23 @@
+---
+source: tests/core/spec.rs
+expression: formatter
+---
+schema
+  @server(enableFederation: false, port: 8000)
+  @upstream(baseURL: "http://jsonplaceholder.typicode.com", batch: {delay: 100, headers: []}, httpCache: 42) {
+  query: Query
+}
+
+type Post @expr(body: {id: "{{.value.id}}", title: "post-title-{{.value.id}}"}) {
+  id: Int!
+  title: String!
+}
+
+type Query {
+  user(id: Int!): User @http(path: "/users/{{.args.id}}")
+}
+
+type User @call(steps: [{query: "user", args: {id: "{{.value.id}}"}}]) {
+  id: Int!
+  name: String!
+}

tests/core/snapshots/federation-subgraph-force-enabled.md_0.snap

@@ -0,0 +1,13 @@
+---
+source: tests/core/spec.rs
+expression: response
+---
+{
+  "status": 200,
+  "headers": {
+    "content-type": "application/json"
+  },
+  "body": {
+    "data": {}
+  }
+}

tests/core/snapshots/federation-subgraph-force-enabled.md_client.snap

@@ -0,0 +1,60 @@
+---
+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
+
+scalar PhoneNumber
+
+type Query {
+  """
+  Apollo federation Query._service resolver
+  """
+  _service: _Service!
+  user(id: Int!): User
+}
+
+scalar UInt128
+
+scalar UInt16
+
+scalar UInt32
+
+scalar UInt64
+
+scalar UInt8
+
+scalar Url
+
+type User {
+  id: Int!
+  name: String!
+}
+
+type _Service {
+  sdl: String
+}
+
+schema {
+  query: Query
+}

tests/core/snapshots/federation-subgraph-force-enabled.md_merged.snap

@@ -0,0 +1,31 @@
+---
+source: tests/core/spec.rs
+expression: formatter
+---
+schema
+  @server(enableFederation: true, port: 8000)
+  @upstream(baseURL: "http://jsonplaceholder.typicode.com", batch: {delay: 100, headers: []}, httpCache: 42) {
+  query: Query
+}
+
+type Post {
+  id: Int!
+  title: String!
+}
+
+type Query {
+  """
+  Apollo federation Query._service resolver
+  """
+  _service: _Service!
+  user(id: Int!): User @http(path: "/users/{{.args.id}}")
+}
+
+type User {
+  id: Int!
+  name: String!
+}
+
+type _Service {
+  sdl: String
+}