From 361b980c948b3533b6a29b25a79708a62bf110ca Mon Sep 17 00:00:00 2001
From: Simon Holthausen <simon.holthausen@vercel.com>
Date: Tue, 16 Aug 2022 16:41:22 +0200
Subject: [PATCH] [fix] Handle function without params when writing TS proxy

Fixes #5927
---
 .changeset/brave-apricots-approve.md          |  5 ++++
 packages/kit/src/core/sync/write_types.js     |  6 ++++-
 .../kit/src/core/sync/write_types.spec.js     | 24 +++++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/brave-apricots-approve.md

diff --git a/.changeset/brave-apricots-approve.md b/.changeset/brave-apricots-approve.md
new file mode 100644
index 000000000000..8ce577e89d33
--- /dev/null
+++ b/.changeset/brave-apricots-approve.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Handle function without params when writing TS proxy
diff --git a/packages/kit/src/core/sync/write_types.js b/packages/kit/src/core/sync/write_types.js
index b9aca69518f8..0eb629f45e70 100644
--- a/packages/kit/src/core/sync/write_types.js
+++ b/packages/kit/src/core/sync/write_types.js
@@ -616,7 +616,11 @@ export function tweak_types(ts, content, names) {
 
 							const rhs = declaration.initializer;
 
-							if (rhs && (ts.isArrowFunction(rhs) || ts.isFunctionExpression(rhs))) {
+							if (
+								rhs &&
+								(ts.isArrowFunction(rhs) || ts.isFunctionExpression(rhs)) &&
+								rhs.parameters.length
+							) {
 								const arg = rhs.parameters[0];
 
 								const add_parens = content[arg.pos - 1] !== '(';
diff --git a/packages/kit/src/core/sync/write_types.spec.js b/packages/kit/src/core/sync/write_types.spec.js
index e614e18783ef..2191e742116e 100644
--- a/packages/kit/src/core/sync/write_types.spec.js
+++ b/packages/kit/src/core/sync/write_types.spec.js
@@ -27,6 +27,30 @@ test('Rewrites types for a TypeScript module', () => {
 	);
 });
 
+test('Rewrites types for a TypeScript module without param', () => {
+	const source = `
+		export const GET: Get = () => {
+			return {
+				a: 1
+			};
+		};
+	`;
+
+	const rewritten = tweak_types(ts, source, new Set(['GET']));
+
+	assert.equal(rewritten?.exports, ['GET']);
+	assert.equal(
+		rewritten?.code,
+		`
+		export const GET = () => {
+			return {
+				a: 1
+			};
+		};
+	`
+	);
+});
+
 test('Rewrites types for a JavaScript module with `function`', () => {
 	const source = `
 		/** @type {import('./$types').Get} */