feature: Adds UniqueVariableNamesRule

Author: NeedleInAJayStack

Sources/GraphQL/Validation/Rules/UniqueVariableNamesRule.swift

@@ -0,0 +1,31 @@
+
+/**
+ * Unique variable names
+ *
+ * A GraphQL operation is only valid if all its variables are uniquely named.
+ */
+func UniqueVariableNamesRule(context: ValidationContext) -> Visitor {
+    return Visitor(
+        enter: { node, _, _, _, _ in
+            if let operation = node as? OperationDefinition {
+                let variableDefinitions = operation.variableDefinitions
+
+                let seenVariableDefinitions = Dictionary(grouping: variableDefinitions) { node in
+                    node.variable.name.value
+                }
+
+                for (variableName, variableNodes) in seenVariableDefinitions {
+                    if variableNodes.count > 1 {
+                        context.report(
+                            error: GraphQLError(
+                                message: "There can be only one variable named \"$\(variableName)\".",
+                                nodes: variableNodes.map { $0.variable.name }
+                            )
+                        )
+                    }
+                }
+            }
+            return .continue
+        }
+    )
+}

Sources/GraphQL/Validation/SpecifiedRules.swift

@@ -16,7 +16,7 @@ public let specifiedRules: [(ValidationContext) -> Visitor] = [
     NoUnusedFragmentsRule,
     PossibleFragmentSpreadsRule,
     NoFragmentCyclesRule,
-//    UniqueVariableNamesRule,
+    UniqueVariableNamesRule,
 //    NoUndefinedVariablesRule,
     NoUnusedVariablesRule,
 //    KnownDirectivesRule,

Tests/GraphQLTests/ValidationTests/UniqueVariableNamesRuleTests.swift

@@ -0,0 +1,54 @@
+@testable import GraphQL
+import XCTest
+
+class UniqueVariableNamesRuleTests: ValidationTestCase {
+    override func setUp() {
+        rule = UniqueVariableNamesRule
+    }
+
+    func testUniqueVariableNames() throws {
+        try assertValid(
+            """
+            query A($x: Int, $y: String) { __typename }
+            query B($x: String, $y: Int) { __typename }
+            """
+        )
+    }
+
+    func testDuplicateVariableNames() throws {
+        let errors = try assertInvalid(
+            errorCount: 3,
+            query:
+            """
+            query A($x: Int, $x: Int, $x: String) { __typename }
+            query B($x: String, $x: Int) { __typename }
+            query C($x: Int, $x: Int) { __typename }
+            """
+        )
+        try assertValidationError(
+            error: errors[0],
+            locations: [
+                (line: 1, column: 10),
+                (line: 1, column: 19),
+                (line: 1, column: 28),
+            ],
+            message: #"There can be only one variable named "$x"."#
+        )
+        try assertValidationError(
+            error: errors[1],
+            locations: [
+                (line: 2, column: 10),
+                (line: 2, column: 22),
+            ],
+            message: #"There can be only one variable named "$x"."#
+        )
+        try assertValidationError(
+            error: errors[2],
+            locations: [
+                (line: 3, column: 10),
+                (line: 3, column: 19),
+            ],
+            message: #"There can be only one variable named "$x"."#
+        )
+    }
+}