feat(discriminator): improve the ergonomics to identify and resolve u…

…nion and interface types (#3000)

Co-authored-by: meskill <[email protected]>
Co-authored-by: Tushar Mathur <[email protected]>

.cache/index-v5/0d/50/9fa0240aa36806aa13c3b26d4be0f807e53f

@@ -1,2 +1,2 @@
 
-f384680608b55c586f4b41eecb43ce8a97a951633d44d839b5bedfc9a1e9afa0	{"key":"GET:https://api.deezer.com/user/2529","integrity":"sha256-7cEa/OBMrNTvAlnFoc6LzTOhbj2BEdSg92Y5o88G0Io=","time":1719748996854,"size":1325,"metadata":null,"raw_metadata":null}
+a59788fe402c268993231b56f1174e56dc5ae3d2f26a59a7d5c0550ef131aecc	{"key":"GET:https://api.deezer.com/user/2529","integrity":"sha256-riGjfZuazQxaVeS6o8Ahh07jjFB+wEgoRbIfn/FBLCU=","time":1729918929552,"size":1318,"metadata":null,"raw_metadata":null}

.cache/index-v5/18/aa/398fea47d489e7c87691edde2b0f4fa5f3b4

@@ -0,0 +1,2 @@
+
+f088c120fc7948480ab24a8dee7b2a891ba434f88ac079648297b3b0a5d757da	{"key":"GET:http://jsonplaceholder.typicode.com/photos","integrity":"sha256-yTN0m7xBplwOBeNMFBBHlHpng8ymEKlTuV67XnqzmU8=","time":1729918926505,"size":133192,"metadata":null,"raw_metadata":null}

.cache/index-v5/30/45/972e74875e2fa855fc12ab452971117dda92

@@ -0,0 +1,2 @@
+
+6ef5556c3f41b191f1a147831751b37094605e9e999176003106699a3f575b67	{"key":"GET:http://jsonplaceholder.typicode.com/users/1","integrity":"sha256-3LAtJul9HZH1TtK3CxQS68LV42jAA8MRS/8648sfX7k=","time":1729918924922,"size":1399,"metadata":null,"raw_metadata":null}

.cache/index-v5/3e/f6/cb54dade99e3f57978e88477b915d0eff694

@@ -0,0 +1,2 @@
+
+2e9cfec608929d69b2925046b5aaba277d66fada8a22d7dc178520c93965646a	{"key":"GET:http://jsonplaceholder.typicode.com/todos","integrity":"sha256-niW7YTq5n8UwtYw3nC7e3ctJf138K/iDlGn7f5jwFGw=","time":1729918926899,"size":5154,"metadata":null,"raw_metadata":null}

.cache/index-v5/45/7e/47040ac50b852f1a38fe4479070e56b299b1

@@ -1,2 +1,2 @@
 
-7e62555ef97159ff6a499e53b4f01e636d2709d05e51ab673877e0550cb229f8	{"key":"GET:https://api.deezer.com/chart","integrity":"sha256-tFJf2JmW1PaicOFNdPf3CRpU6s07L9oFkdIB5rv8aIE=","time":1719748996498,"size":8483,"metadata":null,"raw_metadata":null}
+8f6c1c035d52ff54717776ad82cb71b18403a4dbd90c870da0f039237e81e935	{"key":"GET:https://api.deezer.com/chart","integrity":"sha256-G/8Y4XSNXuS8SqNP6E5Ysj2NgvT9oKXw4+12FYNWY4s=","time":1729918929051,"size":8924,"metadata":null,"raw_metadata":null}

.cache/index-v5/48/74/7608a210fc01562ecedac30523d028b39fea

@@ -0,0 +1,2 @@
+
+30740765bee9d84c3b8849201f2d110f4a9e62baa7f7cfd647d9b642506e959a	{"key":"GET:http://jsonplaceholder.typicode.com/comments/1","integrity":"sha256-T+/bHAQSw7Vv7AqjqRu7YENhkjIB/4aZ3ZbQkLsVTEU=","time":1729918925818,"size":1278,"metadata":null,"raw_metadata":null}

.cache/index-v5/53/10/a53948d6f8b203986a6e64657958db472bb8

@@ -1,2 +1,2 @@
 
-438e58713668bd564551a5d48750a807045c6e5ef90ea9f6d9c1f578fc434176	{"key":"GET:https://api.deezer.com/editorial","integrity":"sha256-Kcj7cNjVEJlTssD+MoypS9dn8wVbX/zDlYY2F5VYQbw=","time":1719748996690,"size":2480,"metadata":null,"raw_metadata":null}
+41e73f4aed7bd3f3b0d117119ed0b4c84a9d4dbd95145bf8d6868387254aab47	{"key":"GET:https://api.deezer.com/editorial","integrity":"sha256-VSfCfyoSXsRym8vfwPf1V8s65nHh8Spcd7c+u1HLOzA=","time":1729918929327,"size":2476,"metadata":null,"raw_metadata":null}

.cache/index-v5/55/ea/c729936c292df58fba36c3ab995beb919370

@@ -0,0 +1,2 @@
+
+4ca1a70bb5223ad95086d9d5d8df9432bc00fd9e469368a8a5515fb6b87457d9	{"key":"GET:http://jsonplaceholder.typicode.com/photos/1","integrity":"sha256-Dp3ZVHTx0q+3iKRejP9Tm4L714YY6ljgCoGDFP+pVTk=","time":1729918926720,"size":1211,"metadata":null,"raw_metadata":null}

.cache/index-v5/5a/56/eedeb5e5029bf1a8089268309d1d99b95b82

@@ -0,0 +1,2 @@
+
+81f4568d53fd0b6c540f928305fc023aed4b5cf0770b1631a43ce349d9ce178a	{"key":"GET:http://jsonplaceholder.typicode.com/users","integrity":"sha256-QoEZrIUc0aTSG3fFiFySshqLuxegZ2hTxItaRfFJKuk=","time":1729918924776,"size":2910,"metadata":null,"raw_metadata":null}

.cache/index-v5/5f/3b/9bca68df9ad96b96e0279b6cb9c27423df9d

@@ -0,0 +1,2 @@
+
+5525e3e19d276c5f9490a19d2aea414ff5e432020efe61a971e196bd878b6183	{"key":"GET:http://jsonplaceholder.typicode.com/comments","integrity":"sha256-1ZlFPsRBt+1R+/QwsLVXQCXD0W7FSGFUJA1o8ed6f/0=","time":1729918925646,"size":41831,"metadata":null,"raw_metadata":null}

.cache/index-v5/6b/2c/6e37b86a06ca566711c8721446f88a402f16

@@ -0,0 +1,2 @@
+
+ec5ec64e295520cd8a325e5ab24bd9d229c1bc33555a127b84a05302fcd1d8f7	{"key":"GET:http://jsonplaceholder.typicode.com/todos/1","integrity":"sha256-Gem2y7bSLS0hB0HxpKCYHQFN4hun0Zab1GwGhlVW+k0=","time":1729918927068,"size":1161,"metadata":null,"raw_metadata":null}

.cache/index-v5/85/74/0bcf6123606c834080fc9ae6a80fbc7afd7c

@@ -0,0 +1,2 @@
+
+a862eecb319e2e5360dcc8c3191381f9f9e9d21ca377bfd658921ba7351f4530	{"key":"GET:http://jsonplaceholder.typicode.com/posts","integrity":"sha256-ukqsdn9GgJZcsGyS8049+v5LbqOTL2YoxZOYmE3aUH4=","time":1729918925103,"size":8295,"metadata":null,"raw_metadata":null}

.cache/index-v5/a6/44/a2de334c2a9de8fcbeea800160023b12ef42

@@ -1,2 +1,2 @@
 
-e3ddfeaefe077fc9fa32abdb8a00239c949dca4db1a7d39ca5e47ad71af2bed3	{"key":"GET:https://api.deezer.com/album/302127","integrity":"sha256-Haxku+8WgcUoGCmd6090+ezPSnOSL3mJ7gRAD4jdHRw=","time":1719748992408,"size":2818,"metadata":null,"raw_metadata":null}
+b517c5ac356c6850255b0d1eae8e9c2f54b745855a6835c3d05731bb64e9b2b8	{"key":"GET:https://api.deezer.com/album/302127","integrity":"sha256-fC61r+BgzIizWGMhDPflFgJPzuy+whJGhLFYVTZGGPE=","time":1729918925014,"size":3615,"metadata":null,"raw_metadata":null}

.cache/index-v5/bf/06/5bc0932db3a16ea1d335c4d520f18e2383c5

@@ -1,2 +1,2 @@
 
-a691bf6cbf884ca2c03a3e8493df05f6f63cdb0f88cad63518c0ca3ace899e24	{"key":"GET:https://api.deezer.com/playlist/908622995","integrity":"sha256-8rJYugim4jE+qoNSUZG3gGg26DU4xiFIxmH/UZ2+4h0=","time":1719748996098,"size":10620,"metadata":null,"raw_metadata":null}
+e677f1d2cb99d03c136ae0bbcb0270591aa2cda218f0415a3672c745ac11d09d	{"key":"GET:https://api.deezer.com/playlist/908622995","integrity":"sha256-N/pOfkVlS5lMl31fbVO5h3rAvS2ZaCayr5DRZXVW6iQ=","time":1729918928659,"size":12598,"metadata":null,"raw_metadata":null}

.cache/index-v5/c9/d8/5c58e5e52bd5fa5171267a33b5116be81480

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+
+5583f421fcb4a663df8193db18a94606535c280fec869e92188482d5eec29d6c	{"key":"GET:http://jsonplaceholder.typicode.com/comments?postId=1","integrity":"sha256-WTZWBzJdOdkLP+CVFajHalI/gXaa1JNSAGLLthf9/yY=","time":1729918927233,"size":1765,"metadata":null,"raw_metadata":null}

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-767ccf322505cb99cf5d0ab638d7d0d256c70ddda61d026e858aa7816ca24bbb	{"key":"GET:https://api.deezer.com/track/3135556","integrity":"sha256-KyLgU7OZEr/uZTQY8qWiODefzRG/kt6msu8/yH3M5aU=","time":1719748992121,"size":2349,"metadata":null,"raw_metadata":null}
+d58ef53cd1b1aa0afc9c3e1bf84b3e20b5ffc760ca20027cf442672ca3ac69ca	{"key":"GET:https://api.deezer.com/track/3135556","integrity":"sha256-8PUN4zq5m2XmdmW456/uscwK7FIMdEO3MtK1ouZjz8U=","time":1729918924756,"size":2761,"metadata":null,"raw_metadata":null}

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-339af8c81b286fb519eacb32e2329ca584a9e7ecd4a13a9368412019f5fd5d14	{"key":"GET:https://api.deezer.com/search?q=eminem","integrity":"sha256-9QWZcUbVM8x8F7K8Ud9avXDCN5W4+8l6+2ll+vFFnQw=","time":1719748997307,"size":1159,"metadata":null,"raw_metadata":null}
+192f0b1251536b1de7ab44f59602bc50721175af12eef643da3436a4bf607ecb	{"key":"GET:https://api.deezer.com/search?q=eminem","integrity":"sha256-tfosFMSfh6ejLZf9lu3grDB1aMRdSkUCxflOldP4K6A=","time":1729918930181,"size":1163,"metadata":null,"raw_metadata":null}

.cache/index-v5/e6/57/a828ada010420c50cf18d57762675dab61c6

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-c672b85180b8cb16ae0fd2b2902a6c4d55f581c7a5156c3bdcdde4b7204946b3	{"key":"GET:https://api.deezer.com/artist/27","integrity":"sha256-DaUvO4VLx1JVy4skdkYG/DRmVNU4v3XWjwx1NfMc4WE=","time":1719748992566,"size":1394,"metadata":null,"raw_metadata":null}
+0e037f975b06346f8aac00291998fcb85b90e694e086fbea63c86adf016f2bf9	{"key":"GET:https://api.deezer.com/artist/27","integrity":"sha256-4Cjj+HA93/4EJfhVb103pBja4YMOFoLPo4PtqJSwSLM=","time":1729918925243,"size":1386,"metadata":null,"raw_metadata":null}

.cache/index-v5/eb/cf/474593f41b0bd59755eec4d265aae630f8fb

@@ -0,0 +1,2 @@
+
+0c35f4503eb3bbeead927304839254f130d16ac7be5cb843fe7e85d4e44ad498	{"key":"GET:http://jsonplaceholder.typicode.com/posts/1","integrity":"sha256-8Zu2600BElex5J0jr5Bs2TscP0cJICKnwEqGjXAlGMI=","time":1729918924754,"size":1292,"metadata":null,"raw_metadata":null}

README.md

@@ -56,15 +56,13 @@ docker run -p 8080:8080 -p 8081:8081 ghcr.io/tailcallhq/tailcall/tc-server
 The below file is a standard `.graphQL` file, with a few additions such as `@server` and `@http` directives. So, basically, we specify the GraphQL schema and how to resolve that GraphQL schema in the same file, without having to write any code!
 
 ```graphql
-schema
-  @server(port: 8000, hostname: "0.0.0.0")
-  @upstream(baseURL: "http://jsonplaceholder.typicode.com", httpCache: 42) {
+schema @server(port: 8000, hostname: "0.0.0.0") @upstream(httpCache: 42) {
   query: Query
 }
 
 type Query {
-  posts: [Post] @http(path: "/posts")
-  user(id: Int!): User @http(path: "/users/{{.args.id}}")
+  posts: [Post] @http(url: "http://jsonplaceholder.typicode.com/posts")
+  user(id: Int!): User @http(url: "http://jsonplaceholder.typicode.com/users/{{.args.id}}")
 }
 
 type User {
@@ -81,7 +79,7 @@ type Post {
   userId: Int!
   title: String!
   body: String!
-  user: User @http(path: "/users/{{.value.userId}}")
+  user: User @http(url: "http://jsonplaceholder.typicode.com/users/{{.value.userId}}")
 }
 ```
 

generated/.tailcallrc.graphql

@@ -470,6 +470,19 @@ directive @upstream(
   verifySSL: Boolean
 ) on SCHEMA
 
+"""
+The `@discriminate` directive is used to drive Tailcall discriminator to use a field 
+of an object to resolve the type. For example with the directive applied on a field 
+`@discriminate(field: "object_type")` and the given value `{"foo": "bar", "object_type": 
+"Buzz"}` the resolved type of the object will be `Buzz`. If `field` is not applied 
+it defaults to "type". The `field` does not have to be part of the GraphQL Schema, 
+but it is required to be part of the JSON response. In case this field is missing 
+from the response an appropriate error message will be displayed.
+"""
+directive @discriminate(
+  field: String
+) on FIELD_DEFINITION
+
 """
 Empty scalar type represents an empty value.
 """

generated/.tailcallrc.schema.json

@@ -337,6 +337,19 @@
         }
       }
     },
+    "Discriminate": {
+      "description": "The `@discriminate` directive is used to drive Tailcall discriminator to use a field of an object to resolve the type. For example with the directive applied on a field `@discriminate(field: \"object_type\")` and the given value `{\"foo\": \"bar\", \"object_type\": \"Buzz\"}` the resolved type of the object will be `Buzz`. If `field` is not applied it defaults to \"type\". The `field` does not have to be part of the GraphQL Schema, but it is required to be part of the JSON response. In case this field is missing from the response an appropriate error message will be displayed.",
+      "type": "object",
+      "properties": {
+        "field": {
+          "type": [
+            "string",
+            "null"
+          ]
+        }
+      },
+      "additionalProperties": false
+    },
     "Email": {
       "title": "Email",
       "description": "Field whose value conforms to the standard internet email address format as specified in HTML Spec: https://html.spec.whatwg.org/multipage/input.html#valid-e-mail-address."
@@ -491,6 +504,17 @@
             "$ref": "#/definitions/Directive"
           }
         },
+        "discriminate": {
+          "description": "Used to overwrite the default discrimination strategy",
+          "anyOf": [
+            {
+              "$ref": "#/definitions/Discriminate"
+            },
+            {
+              "type": "null"
+            }
+          ]
+        },
         "doc": {
           "description": "Publicly visible documentation for the field.",
           "type": [

src/core/blueprint/interface_resolver.rs

@@ -1,57 +1,45 @@
-use std::collections::HashSet;
+use std::collections::BTreeSet;
 
 use crate::core::blueprint::FieldDefinition;
-use crate::core::config;
-use crate::core::config::{ConfigModule, Field};
+use crate::core::config::{ConfigModule, Discriminate, Field, Type};
 use crate::core::ir::model::IR;
 use crate::core::ir::Discriminator;
 use crate::core::try_fold::TryFold;
 use crate::core::valid::{Valid, Validator};
 
 fn compile_interface_resolver(
-    config: &ConfigModule,
     interface_name: &str,
-    interface_types: HashSet<String>,
+    interface_types: &BTreeSet<String>,
+    discriminate: &Option<Discriminate>,
 ) -> Valid<Discriminator, String> {
-    Valid::from_iter(&interface_types, |type_name| {
-        Valid::from_option(
-            config
-                .find_type(type_name)
-                .map(|type_| (type_name.as_str(), type_)),
-            "Can't find a type that is member of interface type".to_string(),
-        )
-    })
-    .and_then(|types| {
-        let types: Vec<_> = types.into_iter().collect();
+    let typename_field = discriminate.as_ref().map(|d| d.get_field());
 
-        Discriminator::new(interface_name, &types)
-    })
+    Discriminator::new(
+        interface_name.to_string(),
+        interface_types.clone(),
+        typename_field,
+    )
 }
 
 pub fn update_interface_resolver<'a>(
-) -> TryFold<'a, (&'a ConfigModule, &'a Field, &'a config::Type, &'a str), FieldDefinition, String>
-{
-    TryFold::<(&ConfigModule, &Field, &config::Type, &str), FieldDefinition, String>::new(
+) -> TryFold<'a, (&'a ConfigModule, &'a Field, &'a Type, &'a str), FieldDefinition, String> {
+    TryFold::<(&ConfigModule, &Field, &Type, &str), FieldDefinition, String>::new(
         |(config, field, _, _), mut b_field| {
             let Some(interface_types) = config.interfaces_types_map().get(field.type_of.name())
             else {
                 return Valid::succeed(b_field);
             };
 
-            compile_interface_resolver(
-                config,
-                field.type_of.name(),
-                interface_types.iter().cloned().collect(),
-            )
-            .map(|discriminator| {
-                b_field.resolver = Some(
+            compile_interface_resolver(field.type_of.name(), interface_types, &field.discriminate)
+                .map(|discriminator| {
+                    b_field.resolver = Some(
+                        b_field
+                            .resolver
+                            .unwrap_or(IR::ContextPath(vec![b_field.name.clone()])),
+                    );
+                    b_field.map_expr(move |expr| IR::Discriminate(discriminator, expr.into()));
                     b_field
-                        .resolver
-                        .unwrap_or(IR::ContextPath(vec![b_field.name.clone()])),
-                );
-                b_field.map_expr(move |expr| IR::Discriminate(discriminator, expr.into()));
-                b_field
-            })
+                })
         },
     )
 }