Validate directive arguments

Fix #110

Argument validation was assuming field arguments which led to spurious error.

src/validation/__tests__/KnownArgumentNames.js

@@ -10,7 +10,7 @@
 import { describe, it } from 'mocha';
 import { expectPassesRule, expectFailsRule } from './harness';
 import KnownArgumentNames from '../rules/KnownArgumentNames';
-import { unknownArgMessage } from '../errors';
+import { unknownArgMessage, unknownDirectiveArgMessage } from '../errors';
 
 function unknownArg(argName, fieldName, typeName, line, column) {
   return {
@@ -19,6 +19,13 @@ function unknownArg(argName, fieldName, typeName, line, column) {
   };
 }
 
+function unknownDirectiveArg(argName, directiveName, line, column) {
+  return {
+    message: unknownDirectiveArgMessage(argName, directiveName),
+    locations: [ { line, column } ],
+  };
+}
+
 describe('Validate: Known argument names', () => {
 
   it('single arg is known', () => {
@@ -78,6 +85,24 @@ describe('Validate: Known argument names', () => {
     `);
   });
 
+  it('directive args are known', () => {
+    expectPassesRule(KnownArgumentNames, `
+      {
+        dog @skip(if: true)
+      }
+    `);
+  });
+
+  it('undirective args are invalid', () => {
+    expectFailsRule(KnownArgumentNames, `
+      {
+        dog @skip(unless: true)
+      }
+    `, [
+      unknownDirectiveArg('unless', 'skip', 3, 19),
+    ]);
+  });
+
   it('invalid arg name', () => {
     expectFailsRule(KnownArgumentNames, `
       fragment invalidArgName on Dog {

src/validation/errors.js

@@ -50,6 +50,10 @@ export function unknownArgMessage(argName, fieldName, typeName) {
     `of type ${typeName}.`;
 }
 
+export function unknownDirectiveArgMessage(argName, fieldName) {
+  return `Unknown argument ${argName} on directive ${fieldName}.`;
+}
+
 export function unknownTypeMessage(typeName) {
   return `Unknown type ${typeName}.`;
 }

src/validation/rules/KnownArgumentNames.js

@@ -10,7 +10,7 @@
 
 import type { ValidationContext } from '../index';
 import { GraphQLError } from '../../error';
-import { unknownArgMessage } from '../errors';
+import { unknownArgMessage, unknownDirectiveArgMessage } from '../errors';
 import invariant from '../../jsutils/invariant';
 import find from '../../jsutils/find';
 
@@ -23,17 +23,41 @@ import find from '../../jsutils/find';
  */
 export default function KnownArgumentNames(context: ValidationContext): any {
   return {
-    Argument(node) {
-      var fieldDef = context.getFieldDef();
-      if (fieldDef) {
-        var argDef = find(fieldDef.args, arg => arg.name === node.name.value);
-        if (!argDef) {
-          var parentType = context.getParentType();
-          invariant(parentType);
-          return new GraphQLError(
-            unknownArgMessage(node.name.value, fieldDef.name, parentType.name),
-            [node]
+    Argument(node, key, parent, path, ancestors) {
+      var argumentOf = ancestors[ancestors.length - 1];
+      if (argumentOf.kind === 'Field') {
+        var fieldDef = context.getFieldDef();
+        if (fieldDef) {
+          var fieldArgDef = find(
+            fieldDef.args,
+            arg => arg.name === node.name.value
           );
+          if (!fieldArgDef) {
+            var parentType = context.getParentType();
+            invariant(parentType);
+            return new GraphQLError(
+              unknownArgMessage(
+                node.name.value,
+                fieldDef.name,
+                parentType.name
+              ),
+              [node]
+            );
+          }
+        }
+      } else if (argumentOf.kind === 'Directive') {
+        var directive = context.getDirective();
+        if (directive) {
+          var directiveArgDef = find(
+            directive.args,
+            arg => arg.name === node.name.value
+          );
+          if (!directiveArgDef) {
+            return new GraphQLError(
+              unknownDirectiveArgMessage(node.name.value, directive.name),
+              [node]
+            );
+          }
         }
       }
     }