feat: Adds UniqueOperationTypesRule

Author: NeedleInAJayStack

Sources/GraphQL/Validation/Rules/UniqueOperationTypesRule.swift

@@ -0,0 +1,62 @@
+
+/**
+ * Unique operation types
+ *
+ * A GraphQL document is only valid if it has only one type per operation.
+ */
+func UniqueOperationTypesRule(
+    context: SDLValidationContext
+) -> Visitor {
+    let schema = context.getSchema()
+    var definedOperationTypes: [OperationType: OperationTypeDefinition] = .init()
+    let existingOperationTypes = {
+        var result = [OperationType: GraphQLObjectType]()
+        if let queryType = schema?.queryType {
+            result[.query] = queryType
+        }
+        if let mutationType = schema?.mutationType {
+            result[.mutation] = mutationType
+        }
+        if let subscriptionType = schema?.subscriptionType {
+            result[.subscription] = subscriptionType
+        }
+        return result
+    }()
+
+    return Visitor(
+        enter: { node, _, _, _, _ in
+            if let operation = node as? SchemaDefinition {
+                checkOperationTypes(operation.operationTypes)
+            } else if let operation = node as? SchemaExtensionDefinition {
+                checkOperationTypes(operation.definition.operationTypes)
+            }
+            return .continue
+        }
+    )
+
+    func checkOperationTypes(
+        _ operationTypesNodes: [OperationTypeDefinition]
+    ) {
+        for operationType in operationTypesNodes {
+            let operation = operationType.operation
+
+            if existingOperationTypes[operation] != nil {
+                context.report(
+                    error: GraphQLError(
+                        message: "Type for \(operation) already defined in the schema. It cannot be redefined.",
+                        nodes: [operationType]
+                    )
+                )
+            } else if let alreadyDefinedOperationType = definedOperationTypes[operation] {
+                context.report(
+                    error: GraphQLError(
+                        message: "There can be only one \(operation) type in schema.",
+                        nodes: [alreadyDefinedOperationType, operationType]
+                    )
+                )
+            } else {
+                definedOperationTypes[operation] = operationType
+            }
+        }
+    }
+}

Sources/GraphQL/Validation/SpecifiedRules.swift

@@ -38,7 +38,7 @@ public let specifiedRules: [(ValidationContext) -> Visitor] = [
  */
 public let specifiedSDLRules: [SDLValidationRule] = [
     LoneSchemaDefinitionRule,
-//    UniqueOperationTypesRule,
+    UniqueOperationTypesRule,
 //    UniqueTypeNamesRule,
 //    UniqueEnumValueNamesRule,
 //    UniqueFieldDefinitionNamesRule,