feature: Adds VariablesAreInputTypesRule

Author: NeedleInAJayStack

Sources/GraphQL/Validation/Rules/VariablesAreInputTypesRule.swift

@@ -0,0 +1,33 @@
+
+/**
+ * Variables are input types
+ *
+ * A GraphQL operation is only valid if all the variables it defines are of
+ * input types (scalar, enum, or input object).
+ *
+ * See https://spec.graphql.org/draft/#sec-Variables-Are-Input-Types
+ */
+func VariablesAreInputTypesRule(context: ValidationContext) -> Visitor {
+    return Visitor(
+        enter: { node, _, _, _, _ in
+            if let variableDefinition = node as? VariableDefinition {
+                let variableType = variableDefinition.type
+                if let type = typeFromAST(schema: context.schema, inputTypeAST: variableType) {
+                    guard !isInputType(type: type) else {
+                        return .continue
+                    }
+
+                    let variableName = variableDefinition.variable.name.value
+                    let typeName = print(ast: variableType)
+                    context.report(
+                        error: GraphQLError(
+                            message: "Variable \"$\(variableName)\" cannot be non-input type \"\(typeName)\".",
+                            nodes: [variableType]
+                        )
+                    )
+                }
+            }
+            return .continue
+        }
+    )
+}

Sources/GraphQL/Validation/SpecifiedRules.swift

@@ -8,7 +8,7 @@ public let specifiedRules: [(ValidationContext) -> Visitor] = [
 //    SingleFieldSubscriptionsRule,
     KnownTypeNamesRule,
     FragmentsOnCompositeTypesRule,
-//    VariablesAreInputTypesRule,
+    VariablesAreInputTypesRule,
     ScalarLeafsRule,
     FieldsOnCorrectTypeRule,
 //    UniqueFragmentNamesRule,

Tests/GraphQLTests/ValidationTests/VariablesAreInputTypesRuleTests.swift

@@ -0,0 +1,55 @@
+@testable import GraphQL
+import XCTest
+
+class VariablesAreInputTypesRuleTests: ValidationTestCase {
+    override func setUp() {
+        rule = VariablesAreInputTypesRule
+    }
+
+    func testUnknownTypesAreIgnored() throws {
+        try assertValid(
+            """
+            query Foo($a: Unknown, $b: [[Unknown!]]!) {
+              field(a: $a, b: $b)
+            }
+            """
+        )
+    }
+
+    func testInputTypesAreValid() throws {
+        try assertValid(
+            """
+            query Foo($a: String, $b: [Boolean!]!, $c: ComplexInput) {
+              field(a: $a, b: $b, c: $c)
+            }
+            """
+        )
+    }
+
+    func testOutputTypesAreInvalid() throws {
+        let errors = try assertInvalid(
+            errorCount: 3,
+            query:
+            """
+            query Foo($a: Dog, $b: [[CatOrDog!]]!, $c: Pet) {
+              field(a: $a, b: $b, c: $c)
+            }
+            """
+        )
+        try assertValidationError(
+            error: errors[0],
+            locations: [(line: 1, column: 15)],
+            message: "Variable \"$a\" cannot be non-input type \"Dog\"."
+        )
+        try assertValidationError(
+            error: errors[1],
+            locations: [(line: 1, column: 24)],
+            message: "Variable \"$b\" cannot be non-input type \"[[CatOrDog!]]!\"."
+        )
+        try assertValidationError(
+            error: errors[2],
+            locations: [(line: 1, column: 44)],
+            message: "Variable \"$c\" cannot be non-input type \"Pet\"."
+        )
+    }
+}