From 42878a086477f1301e6c25a2c7f79ea1ddfd31b6 Mon Sep 17 00:00:00 2001
From: Jordan Eldredge <jordan@jordaneldredge.com>
Date: Wed, 21 Jan 2026 16:06:14 -0800
Subject: [PATCH] Readonly arrays

---
 src/Extractor.ts                              |  4 ++
 .../arguments/ReadonlyArrayOfString.ts        |  7 +++
 .../ReadonlyArrayOfString.ts.expected.md      | 53 +++++++++++++++++++
 website/docs/07-changelog/index.md            |  1 +
 4 files changed, 65 insertions(+)
 create mode 100644 src/tests/fixtures/arguments/ReadonlyArrayOfString.ts
 create mode 100644 src/tests/fixtures/arguments/ReadonlyArrayOfString.ts.expected.md

diff --git a/src/Extractor.ts b/src/Extractor.ts
index fc561ba3..27182129 100644
--- a/src/Extractor.ts
+++ b/src/Extractor.ts
@@ -2624,6 +2624,10 @@ class Extractor {
       return this.report(node, E.ambiguousNumberType());
     } else if (ts.isTypeLiteralNode(node)) {
       return this.report(node, E.unsupportedTypeLiteral());
+    } else if (ts.isTypeOperatorNode(node)) {
+      if (node.operator === ts.SyntaxKind.ReadonlyKeyword) {
+        return this.collectType(node.type, ctx);
+      }
     }
     // TODO: Better error message. This is okay if it's a type reference, but everything else is not.
     this.reportUnhandled(node, "type", E.unknownGraphQLType());
diff --git a/src/tests/fixtures/arguments/ReadonlyArrayOfString.ts b/src/tests/fixtures/arguments/ReadonlyArrayOfString.ts
new file mode 100644
index 00000000..18bea754
--- /dev/null
+++ b/src/tests/fixtures/arguments/ReadonlyArrayOfString.ts
@@ -0,0 +1,7 @@
+/** @gqlType */
+export default class SomeType {
+  /** @gqlField */
+  hello(greetings: readonly string[]): string {
+    return `${greetings.join(", ")} world!`;
+  }
+}
diff --git a/src/tests/fixtures/arguments/ReadonlyArrayOfString.ts.expected.md b/src/tests/fixtures/arguments/ReadonlyArrayOfString.ts.expected.md
new file mode 100644
index 00000000..340029c6
--- /dev/null
+++ b/src/tests/fixtures/arguments/ReadonlyArrayOfString.ts.expected.md
@@ -0,0 +1,53 @@
+# arguments/ReadonlyArrayOfString.ts
+
+## Input
+
+```ts title="arguments/ReadonlyArrayOfString.ts"
+/** @gqlType */
+export default class SomeType {
+  /** @gqlField */
+  hello(greetings: readonly string[]): string {
+    return `${greetings.join(", ")} world!`;
+  }
+}
+```
+
+## Output
+
+### SDL
+
+```graphql
+type SomeType {
+  hello(greetings: [String!]!): String
+}
+```
+
+### TypeScript
+
+```ts
+import { GraphQLSchema, GraphQLObjectType, GraphQLString, GraphQLNonNull, GraphQLList } from "graphql";
+export function getSchema(): GraphQLSchema {
+    const SomeTypeType: GraphQLObjectType = new GraphQLObjectType({
+        name: "SomeType",
+        fields() {
+            return {
+                hello: {
+                    name: "hello",
+                    type: GraphQLString,
+                    args: {
+                        greetings: {
+                            type: new GraphQLNonNull(new GraphQLList(new GraphQLNonNull(GraphQLString)))
+                        }
+                    },
+                    resolve(source, args) {
+                        return source.hello(args.greetings);
+                    }
+                }
+            };
+        }
+    });
+    return new GraphQLSchema({
+        types: [SomeTypeType]
+    });
+}
+```
\ No newline at end of file
diff --git a/website/docs/07-changelog/index.md b/website/docs/07-changelog/index.md
index 8e06cdbb..80427bab 100644
--- a/website/docs/07-changelog/index.md
+++ b/website/docs/07-changelog/index.md
@@ -4,6 +4,7 @@
 
 - **Features**
   - Added support for async derived context functions. Derived context functions can now return `Promise<T>` and Grats will automatically generate the necessary `await` expressions in resolver code.
+  - Added support for `readonly T[]` as parsable GraphQL types.
 
 Changes in this section are not yet released. If you need access to these changes before we cut a release, check out our `@main` NPM releases. Each commit on the main branch is [published to NPM](https://www.npmjs.com/package/grats?activeTab=versions) under the `main` tag.