fix: successive optional route parameters can now be empty (#9266)

* Optional chained parameters can be skipped - close #9261

* Update changeset description

Co-authored-by: Ben McCann <[email protected]>

---------

Co-authored-by: Ben McCann <[email protected]>

Author: glennsayers

.changeset/nasty-guests-sing.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: successive optional route parameters can now be empty

packages/kit/src/utils/routing.js

@@ -152,6 +152,14 @@ export function exec(match, params, matchers) {
 
 		if (!param.matcher || matchers[param.matcher](value)) {
 			result[param.name] = value;
+
+			// Now that the params match, reset the buffer if the next param isn't the [...rest]
+			// and the next value is defined, otherwise the buffer will cause us to skip values
+			const next_param = params[i + 1];
+			const next_value = values[i + 1];
+			if (next_param && !next_param.rest && next_value) {
+				buffered = 0;
+			}
 			continue;
 		}
 

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

@@ -187,6 +187,16 @@ const exec_tests = [
 		route: '/[[a=doesntmatch]]/[[b=matches]]/c',
 		path: '/a/b/c',
 		expected: undefined
+	},
+	{
+		route: '/[[slug1=matches]]/[[slug2=matches]]/constant/[[slug3=matches]]',
+		path: '/a/b/constant/c',
+		expected: { slug1: 'a', slug2: 'b', slug3: 'c' }
+	},
+	{
+		route: '/[[slug1=doesntmatch]]/[[slug2=matches]]/constant/[[slug3=matches]]',
+		path: '/b/constant/c',
+		expected: { slug2: 'b', slug3: 'c' }
 	}
 ];