feat: support multiple resolvers on fields

generated/.tailcallrc.graphql

@@ -47,15 +47,15 @@ directive @call(
   of the previous step is passed as input to the next step.
   """
   steps: [Step]
-) on FIELD_DEFINITION | OBJECT
+) repeatable on FIELD_DEFINITION | OBJECT
 
 """
 The `@expr` operators allows you to specify an expression that can evaluate to a 
 value. The expression can be a static value or built form a Mustache template. schema.
 """
 directive @expr(
   body: JSON
-) on FIELD_DEFINITION | OBJECT
+) repeatable on FIELD_DEFINITION | OBJECT
 
 """
 The @graphQL operator allows to specify GraphQL API server request to fetch data 
@@ -95,7 +95,7 @@ directive @graphQL(
   This refers URL of the API.
   """
   url: String!
-) on FIELD_DEFINITION | OBJECT
+) repeatable on FIELD_DEFINITION | OBJECT
 
 """
 The @grpc operator indicates that a field or node is backed by a gRPC API.For instance, 
@@ -149,7 +149,7 @@ directive @grpc(
   This refers to URL of the API.
   """
   url: String!
-) on FIELD_DEFINITION | OBJECT
+) repeatable on FIELD_DEFINITION | OBJECT
 
 """
 The @http operator indicates that a field or node is backed by a REST API.For instance, 
@@ -229,11 +229,11 @@ directive @http(
   This refers to URL of the API.
   """
   url: String!
-) on FIELD_DEFINITION | OBJECT
+) repeatable on FIELD_DEFINITION | OBJECT
 
 directive @js(
   name: String!
-) on FIELD_DEFINITION | OBJECT
+) repeatable on FIELD_DEFINITION | OBJECT
 
 """
 The @link directive allows you to import external resources, such as configuration 

generated/.tailcallrc.schema.json

@@ -400,81 +400,13 @@
     },
     "Field": {
       "description": "A field definition containing all the metadata information about resolving a field.",
-      "type": "object",
-      "oneOf": [
-        {
-          "type": "object",
-          "required": [
-            "http"
-          ],
-          "properties": {
-            "http": {
-              "$ref": "#/definitions/Http"
-            }
-          },
-          "additionalProperties": false
-        },
-        {
-          "type": "object",
-          "required": [
-            "grpc"
-          ],
-          "properties": {
-            "grpc": {
-              "$ref": "#/definitions/Grpc"
-            }
-          },
-          "additionalProperties": false
-        },
-        {
-          "type": "object",
-          "required": [
-            "graphql"
-          ],
-          "properties": {
-            "graphql": {
-              "$ref": "#/definitions/GraphQL"
-            }
-          },
-          "additionalProperties": false
-        },
-        {
-          "type": "object",
-          "required": [
-            "call"
-          ],
-          "properties": {
-            "call": {
-              "$ref": "#/definitions/Call"
-            }
-          },
-          "additionalProperties": false
-        },
-        {
-          "type": "object",
-          "required": [
-            "js"
-          ],
-          "properties": {
-            "js": {
-              "$ref": "#/definitions/JS"
-            }
-          },
-          "additionalProperties": false
-        },
-        {
-          "type": "object",
-          "required": [
-            "expr"
-          ],
-          "properties": {
-            "expr": {
-              "$ref": "#/definitions/Expr"
-            }
-          },
-          "additionalProperties": false
-        }
+      "type": [
+        "object",
+        "array"
       ],
+      "items": {
+        "$ref": "#/definitions/Resolver"
+      },
       "properties": {
         "args": {
           "description": "Map of argument name and its definition.",
@@ -1021,6 +953,82 @@
         }
       }
     },
+    "Resolver": {
+      "oneOf": [
+        {
+          "type": "object",
+          "required": [
+            "http"
+          ],
+          "properties": {
+            "http": {
+              "$ref": "#/definitions/Http"
+            }
+          },
+          "additionalProperties": false
+        },
+        {
+          "type": "object",
+          "required": [
+            "grpc"
+          ],
+          "properties": {
+            "grpc": {
+              "$ref": "#/definitions/Grpc"
+            }
+          },
+          "additionalProperties": false
+        },
+        {
+          "type": "object",
+          "required": [
+            "graphql"
+          ],
+          "properties": {
+            "graphql": {
+              "$ref": "#/definitions/GraphQL"
+            }
+          },
+          "additionalProperties": false
+        },
+        {
+          "type": "object",
+          "required": [
+            "call"
+          ],
+          "properties": {
+            "call": {
+              "$ref": "#/definitions/Call"
+            }
+          },
+          "additionalProperties": false
+        },
+        {
+          "type": "object",
+          "required": [
+            "js"
+          ],
+          "properties": {
+            "js": {
+              "$ref": "#/definitions/JS"
+            }
+          },
+          "additionalProperties": false
+        },
+        {
+          "type": "object",
+          "required": [
+            "expr"
+          ],
+          "properties": {
+            "expr": {
+              "$ref": "#/definitions/Expr"
+            }
+          },
+          "additionalProperties": false
+        }
+      ]
+    },
     "RootSchema": {
       "type": "object",
       "properties": {
@@ -1336,81 +1344,13 @@
     },
     "Type": {
       "description": "Represents a GraphQL type. A type can be an object, interface, enum or scalar.",
-      "type": "object",
-      "oneOf": [
-        {
-          "type": "object",
-          "required": [
-            "http"
-          ],
-          "properties": {
-            "http": {
-              "$ref": "#/definitions/Http"
-            }
-          },
-          "additionalProperties": false
-        },
-        {
-          "type": "object",
-          "required": [
-            "grpc"
-          ],
-          "properties": {
-            "grpc": {
-              "$ref": "#/definitions/Grpc"
-            }
-          },
-          "additionalProperties": false
-        },
-        {
-          "type": "object",
-          "required": [
-            "graphql"
-          ],
-          "properties": {
-            "graphql": {
-              "$ref": "#/definitions/GraphQL"
-            }
-          },
-          "additionalProperties": false
-        },
-        {
-          "type": "object",
-          "required": [
-            "call"
-          ],
-          "properties": {
-            "call": {
-              "$ref": "#/definitions/Call"
-            }
-          },
-          "additionalProperties": false
-        },
-        {
-          "type": "object",
-          "required": [
-            "js"
-          ],
-          "properties": {
-            "js": {
-              "$ref": "#/definitions/JS"
-            }
-          },
-          "additionalProperties": false
-        },
-        {
-          "type": "object",
-          "required": [
-            "expr"
-          ],
-          "properties": {
-            "expr": {
-              "$ref": "#/definitions/Expr"
-            }
-          },
-          "additionalProperties": false
-        }
+      "type": [
+        "object",
+        "array"
       ],
+      "items": {
+        "$ref": "#/definitions/Resolver"
+      },
       "required": [
         "fields"
       ],

src/cli/tc/init.rs

@@ -87,7 +87,7 @@
 fn main_config() -> Config {
     let field = Field {
         type_of: Type::from("String".to_owned()).into_required(),
-        resolver: Some(Resolver::Expr(Expr { body: "Hello, World!".into() })),
+        resolvers: Resolver::Expr(Expr { body: "Hello, World!".into() }).into(),
         ..Default::default()
     };
 

src/core/blueprint/definitions.rs

@@ -107,14 +107,19 @@ fn process_field_within_type(context: ProcessFieldWithinTypeContext) -> Valid<Ty
     let path_resolver_error_handler = context.path_resolver_error_handler;
 
     if let Some(next_field) = type_info.fields.get(field_name) {
-        if let Some(resolver) = &next_field.resolver {
-            return path_resolver_error_handler(
-                &resolver.directive_name(),
-                field.type_of.name(),
-                field_name,
-                context.original_path,
-            )
-            .and(process_path(ProcessPathContext {
+        if !next_field.resolvers.is_empty() {
+            let mut valid = Valid::succeed(field.type_of.clone());
+
+            for resolver in next_field.resolvers.iter() {
+                valid = valid.and(path_resolver_error_handler(
+                    &resolver.directive_name(),
+                    field.type_of.name(),
+                    field_name,
+                    context.original_path,
+                ));
+            }
+
+            return valid.and(process_path(ProcessPathContext {
                 type_info,
                 is_required,
                 config_module,
@@ -424,12 +429,13 @@ fn to_fields(
                 &add_field.name,
             )
             .and_then(|field_definition| {
-                let added_field_path = match source_field.resolver {
-                    Some(_) => add_field.path[1..]
+                let added_field_path = if source_field.resolvers.is_empty() {
+                    add_field.path.clone()
+                } else {
+                    add_field.path[1..]
                         .iter()
                         .map(|s| s.to_owned())
-                        .collect::<Vec<_>>(),
-                    None => add_field.path.clone(),
+                        .collect::<Vec<_>>()
                 };
                 let invalid_path_handler = |field_name: &str,
                                             _added_field_path: &[String],
@@ -499,13 +505,8 @@ pub fn to_field_definition(
     name: &str,
 ) -> Valid<FieldDefinition, String> {
     update_args()
-        .and(update_http().trace(config::Http::trace_name().as_str()))
-        .and(update_grpc(operation_type).trace(config::Grpc::trace_name().as_str()))
-        .and(update_const_field().trace(config::Expr::trace_name().as_str()))
-        .and(update_js_field().trace(config::JS::trace_name().as_str()))
-        .and(update_graphql(operation_type).trace(config::GraphQL::trace_name().as_str()))
+        .and(update_resolver(operation_type, object_name))
         .and(update_modify().trace(config::Modify::trace_name().as_str()))
-        .and(update_call(operation_type, object_name).trace(config::Call::trace_name().as_str()))
         .and(fix_dangling_resolvers())
         .and(update_cache_resolvers())
         .and(update_protected(object_name).trace(Protected::trace_name().as_str()))

src/core/blueprint/from_config.rs

@@ -88,7 +88,7 @@ pub fn to_json_schema(type_of: &Type, config: &Config) -> JsonSchema {
             if let Some(type_) = type_ {
                 let mut schema_fields = BTreeMap::new();
                 for (name, field) in type_.fields.iter() {
-                    if field.resolver.is_none() {
+                    if field.resolvers.is_empty() {
                         schema_fields.insert(name.clone(), to_json_schema(&field.type_of, config));
                     }
                 }