[fix] continuous optionals should not throw conflict error (#7939)

fixes #7925

.changeset/six-ravens-attack.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+[fix] continuous optionals should not throw conflict error

packages/kit/src/core/sync/create_manifest_data/index.js

@@ -486,10 +486,11 @@ function prevent_conflicts(routes) {
 			const matcher = split[i];
 			const next = split[i + 1];
 
-			permutations = [
-				...permutations.map((x) => x + next),
-				...permutations.map((x) => x + `<${matcher}>${next}`)
-			];
+			permutations = permutations.reduce((a, b) => {
+				a.push(b + next);
+				if (!(matcher === '*' && b.endsWith('//'))) a.push(b + `<${matcher}>${next}`);
+				return a;
+			}, /** @type {string[]} */ ([]));
 		}
 
 		for (const permutation of permutations) {

packages/kit/src/core/sync/create_manifest_data/index.spec.js

@@ -386,6 +386,35 @@ test('optional parameters', () => {
 	]);
 });
 
+test('nested optionals', () => {
+	const { nodes, routes } = create('samples/nested-optionals');
+	assert.equal(nodes.map(simplify_node), [
+		default_layout,
+		default_error,
+		{ component: 'samples/nested-optionals/[[a]]/[[b]]/+page.svelte' }
+	]);
+
+	assert.equal(routes.map(simplify_route), [
+		{
+			id: '/',
+			pattern: '/^/$/'
+		},
+		{
+			id: '/[[a]]/[[b]]',
+			pattern: '/^(?:/([^/]+))?(?:/([^/]+))?/?$/',
+			page: {
+				layouts: [0],
+				errors: [1],
+				leaf: nodes.findIndex((node) => node.component?.includes('/[[a]]/[[b]]'))
+			}
+		},
+		{
+			id: '/[[a]]',
+			pattern: '/^(?:/([^/]+))?/?$/'
+		}
+	]);
+});
+
 test('ignores files and directories with leading underscores', () => {
 	const { routes } = create('samples/hidden-underscore');