fix: allow optional param in middle of route (#10736)

.changeset/tricky-geckos-poke.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: allow optional param in middle of route

packages/kit/src/utils/routing.js

@@ -136,6 +136,7 @@ export function exec(match, params, matchers) {
 	const result = {};
 
 	const values = match.slice(1);
+	const values_needing_match = values.filter((value) => value !== undefined);
 
 	let buffered = 0;
 
@@ -170,6 +171,15 @@ export function exec(match, params, matchers) {
 			if (next_param && !next_param.rest && next_param.optional && next_value && param.chained) {
 				buffered = 0;
 			}
+
+			// There are no more params and no more values, but all non-empty values have been matched
+			if (
+				!next_param &&
+				!next_value &&
+				Object.keys(result).length === values_needing_match.length
+			) {
+				buffered = 0;
+			}
 			continue;
 		}
 

packages/kit/src/utils/routing.spec.js

@@ -197,6 +197,16 @@ const exec_tests = [
 		path: '/b/constant/c',
 		expected: { slug2: 'b', slug3: 'c' }
 	},
+	{
+		route: '/[[slug1=doesntmatch]]/[[slug2=matches]]/[[slug3=matches]]',
+		path: '/b/c',
+		expected: { slug2: 'b', slug3: 'c' }
+	},
+	{
+		route: '/[slug1]/[[lang=doesntmatch]]/[[page=matches]]',
+		path: '/a/2',
+		expected: { slug1: 'a', lang: undefined, page: '2' }
+	},
 	{
 		route: '/[[slug1=doesntmatch]]/[slug2=matches]/[slug3]',
 		path: '/a/b/c',