fix(filterSchema): provide actual type name for root field

.changeset/warm-ducks-smash.md

@@ -0,0 +1,5 @@
+---
+"@graphql-tools/utils": patch
+---
+
+fix filterSchema argument filter for schema with non-default root types

packages/utils/src/filterSchema.ts

@@ -94,7 +94,7 @@ function filterRootFields(
         delete config.fields[fieldName];
       } else if (argumentFilter && field.args) {
         for (const argName in field.args) {
-          if (!argumentFilter(operation, fieldName, argName, field.args[argName])) {
+          if (!argumentFilter(type.name, fieldName, argName, field.args[argName])) {
             delete field.args[argName];
           }
         }

packages/utils/tests/filterSchema.test.ts

@@ -236,4 +236,33 @@ describe('filterSchema', () => {
         ['field'].args.map(arg => arg.name),
     ).toEqual(['keep']);
   });
+
+  it('filters root field arguments for non-default query type', () => {
+    const schema = makeExecutableSchema({
+      typeDefs: /* GraphQL */ `
+        schema {
+          query: Root
+        }
+        type Root {
+          field(keep: String, omit: String): String
+        }
+      `,
+    });
+
+    const filtered = filterSchema({
+      schema,
+      argumentFilter(typeName, fieldName, argName) {
+        if (typeName === 'Root' && fieldName === 'field' && argName === 'omit') {
+          return false;
+        }
+        return true;
+      },
+    });
+
+    expect(
+      (filtered.getType('Root') as GraphQLObjectType)
+        .getFields()
+        ['field'].args.map(arg => arg.name),
+    ).toEqual(['keep']);
+  });
 });