feature: Adds VariablesInAllowedPositionRule

Author: NeedleInAJayStack

Sources/GraphQL/Validation/Rules/VariablesInAllowedPositionRule.swift

@@ -0,0 +1,90 @@
+
+/**
+ * Variables in allowed position
+ *
+ * Variable usages must be compatible with the arguments they are passed to.
+ *
+ * See https://spec.graphql.org/draft/#sec-All-Variable-Usages-are-Allowed
+ */
+func VariablesInAllowedPositionRule(context: ValidationContext) -> Visitor {
+    var varDefMap: [String: VariableDefinition] = [:]
+    return Visitor(
+        enter: { node, _, _, _, _ in
+            switch node {
+            case _ as OperationDefinition:
+                varDefMap = [:]
+            case let variableDefinition as VariableDefinition:
+                varDefMap[variableDefinition.variable.name.value] = variableDefinition
+            default:
+                break
+            }
+            return .continue
+        },
+        leave: { node, _, _, _, _ in
+            switch node {
+            case let operation as OperationDefinition:
+                let usages = context.getRecursiveVariableUsages(operation: operation)
+
+                for usage in usages {
+                    let varName = usage.node.name.value
+                    let schema = context.schema
+
+                    if
+                        let varDef = varDefMap[varName],
+                        let type = usage.type,
+                        let varType = typeFromAST(schema: schema, inputTypeAST: varDef.type)
+                    {
+                        // A var type is allowed if it is the same or more strict (e.g. is
+                        // a subtype of) than the expected type. It can be more strict if
+                        // the variable type is non-null when the expected type is nullable.
+                        // If both are list types, the variable item type can be more strict
+                        // than the expected item type (contravariant).
+                        let isAllowed = (try? allowedVariableUsage(
+                            schema: schema,
+                            varType: varType,
+                            varDefaultValue: varDef.defaultValue,
+                            locationType: type,
+                            locationDefaultValue: usage.defaultValue
+                        )) ?? false
+                        if !isAllowed {
+                            context.report(
+                                error: GraphQLError(
+                                    message: "Variable \"$\(varName)\" of type \"\(varType)\" used in position expecting type \"\(type)\".",
+                                    nodes: [varDef, usage.node]
+                                )
+                            )
+                        }
+                    }
+                }
+            default:
+                break
+            }
+            return .continue
+        }
+    )
+}
+
+/**
+ * Returns true if the variable is allowed in the location it was found,
+ * which includes considering if default values exist for either the variable
+ * or the location at which it is located.
+ */
+func allowedVariableUsage(
+    schema: GraphQLSchema,
+    varType: GraphQLType,
+    varDefaultValue: Value?,
+    locationType: GraphQLType,
+    locationDefaultValue: Map?
+) throws -> Bool {
+    if let locationType = locationType as? GraphQLNonNull, !(varType is GraphQLNonNull) {
+        let hasNonNullVariableDefaultValue = varDefaultValue != nil && varDefaultValue?
+            .kind != .nullValue
+        let hasLocationDefaultValue = locationDefaultValue != .undefined
+        if !hasNonNullVariableDefaultValue && !hasLocationDefaultValue {
+            return false
+        }
+        let nullableLocationType = locationType.ofType
+        return try isTypeSubTypeOf(schema, varType, nullableLocationType)
+    }
+    return try isTypeSubTypeOf(schema, varType, locationType)
+}

Sources/GraphQL/Validation/SpecifiedRules.swift

@@ -29,7 +29,7 @@ public let specifiedRules: [(ValidationContext) -> Visitor] = [
     ValuesOfCorrectTypeRule,
 //    ProvidedRequiredArgumentsRule,
     ProvidedNonNullArgumentsRule,
-//    VariablesInAllowedPositionRule,
+    VariablesInAllowedPositionRule,
 //    OverlappingFieldsCanBeMergedRule,
     UniqueInputFieldNamesRule,
 ]

Tests/GraphQLTests/StarWarsTests/StarWarsQueryTests.swift

@@ -186,7 +186,7 @@ class StarWarsQueryTests: XCTestCase {
 
         let query =
             """
-            query FetchHeroByEpisodeQuery($episode: String) {
+            query FetchHeroByEpisodeQuery($episode: Episode) {
                 hero(episode: $episode) {
                     name
                 }