always re-run preload functions when query string changes - fixes #701

test/apps/preloading/src/routes/echo/index.svelte

@@ -0,0 +1,17 @@
+<script context="module">
+	export function preload(page) {
+		return {
+			query: page.query
+		};
+	}
+</script>
+
+<script>
+	export let query;
+</script>
+
+<pre>{JSON.stringify(query)}</pre>
+
+<a href="echo?foo=1">foo=1</a>
+<a href="echo?foo=2">foo=2</a>
+<a href="echo?foo=3">foo=3</a>

test/apps/preloading/test.ts

@@ -109,4 +109,23 @@ describe('preloading', function() {
 	it('survives the tests with no server errors', () => {
 		assert.deepEqual(r.errors, []);
 	});
+
+	it('re-runs preload when page.query changes', async () => {
+		await r.load('/echo?foo=1');
+		await r.sapper.start();
+		await r.sapper.prefetchRoutes();
+
+		assert.equal(
+			await r.text('pre'),
+			`{"foo":"1"}`
+		);
+
+		await r.page.click('a[href="echo?foo=2"]');
+		await r.wait();
+
+		assert.equal(
+			await r.text('pre'),
+			`{"foo":"2"}`
+		);
+	});
 });