feature: Adds KnownFragmentNamesRule

Author: NeedleInAJayStack

Sources/GraphQL/Validation/Rules/KnownFragmentNamesRule.swift

@@ -0,0 +1,29 @@
+import Foundation
+
+/**
+ * Known fragment names
+ *
+ * A GraphQL document is only valid if all `...Fragment` fragment spreads refer
+ * to fragments defined in the same document.
+ *
+ * See https://spec.graphql.org/draft/#sec-Fragment-spread-target-defined
+ */
+func KnownFragmentNamesRule(context: ValidationContext) -> Visitor {
+    return Visitor(
+        enter: { node, _, _, _, _ in
+            if let fragmentReference = node as? FragmentSpread {
+                let fragmentName = fragmentReference.name.value
+                let fragmentDefinition = context.getFragment(name: fragmentName)
+
+                if fragmentDefinition == nil {
+                    context.report(error: GraphQLError(
+                        message: "Unknown fragment \"\(fragmentName)\".",
+                        nodes: [fragmentReference.name]
+                    ))
+                }
+            }
+
+            return .continue
+        }
+    )
+}

Sources/GraphQL/Validation/SpecifiedRules.swift

@@ -12,7 +12,7 @@ public let specifiedRules: [(ValidationContext) -> Visitor] = [
     ScalarLeafsRule,
     FieldsOnCorrectTypeRule,
     UniqueFragmentNamesRule,
-//    KnownFragmentNamesRule,
+    KnownFragmentNamesRule,
     NoUnusedFragmentsRule,
     PossibleFragmentSpreadsRule,
 //    NoFragmentCyclesRule,

Tests/GraphQLTests/ValidationTests/KnownFragmentNamesTests.swift

@@ -0,0 +1,73 @@
+@testable import GraphQL
+import XCTest
+
+class KnownFragmentNamesTests: ValidationTestCase {
+    override func setUp() {
+        rule = KnownFragmentNamesRule
+    }
+
+    func testKnownFragmentNamesAreValid() throws {
+        try assertValid(
+            """
+            {
+              human(id: 4) {
+                ...HumanFields1
+                ... on Human {
+                  ...HumanFields2
+                }
+                ... {
+                  name
+                }
+              }
+            }
+            fragment HumanFields1 on Human {
+              name
+              ...HumanFields3
+            }
+            fragment HumanFields2 on Human {
+              name
+            }
+            fragment HumanFields3 on Human {
+              name
+            }
+            """
+        )
+    }
+
+    func testUnknownFragmentNamesAreInvalid() throws {
+        let errors = try assertInvalid(
+            errorCount: 3,
+            query:
+            """
+            {
+              human(id: 4) {
+                ...UnknownFragment1
+                ... on Human {
+                  ...UnknownFragment2
+                }
+              }
+            }
+            fragment HumanFields on Human {
+              name
+              ...UnknownFragment3
+            }
+            """
+        )
+
+        try assertValidationError(
+            error: errors[0],
+            locations: [(line: 3, column: 8)],
+            message: "Unknown fragment \"UnknownFragment1\"."
+        )
+        try assertValidationError(
+            error: errors[1],
+            locations: [(line: 5, column: 10)],
+            message: "Unknown fragment \"UnknownFragment2\"."
+        )
+        try assertValidationError(
+            error: errors[2],
+            locations: [(line: 11, column: 6)],
+            message: "Unknown fragment \"UnknownFragment3\"."
+        )
+    }
+}