fix: prevent 404 for routes consisting solely of an optional parameter (#2798)

Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people

docs/latest/concepts/file-routing.md

@@ -78,6 +78,7 @@ they might match:
 | `blog/[slug]/comments.ts`   | `/blog/:slug/comments` | `/blog/foo/comments`                    |
 | `old/[...path].ts`          | `/old/:path*`          | `/old/foo`, `/old/bar/baz`              |
 | `docs/[[version]]/index.ts` | `/docs{/:version}?`    | `/docs`, `/docs/latest`, `/docs/canary` |
+| `[[name]].ts`               | `/{:name}?`            | `/`, `/foo`, `/bar`                     |
 
 Advanced use-cases can require that a more complex pattern be used for matching.
 A custom [URL pattern][urlpattern] can be specified in the route configuration.

packages/fresh/src/router.ts

@@ -196,6 +196,7 @@ export function pathToPattern(
 
   let route = "";
 
+  let nonOptionalSegments = 0;
   for (let i = 0; i < parts.length; i++) {
     const part = parts[i];
 
@@ -268,14 +269,29 @@ export function pathToPattern(
       }
     }
 
-    route += (optional ? "" : "/") + pattern;
+    if (optional) {
+      route += pattern;
+    } else {
+      nonOptionalSegments++;
+      route += "/" + pattern;
+    }
   }
 
   // Case: /(group)/index.tsx
   if (route === "") {
     route = "/";
   }
 
+  // Handles all cases where a route starts with
+  // an optional parameter and does not contain
+  // any non-group and non-optional segments after
+  // Case: /[[id]].tsx
+  // Case: /(group)/[[id]].tsx
+  // Case: /(group)/[[name]]/(group2)/index.tsx
+  if (route.startsWith(`{/`) && nonOptionalSegments === 0) {
+    route = route.replace("{/", "/{");
+  }
+
   return route;
 }
 

packages/fresh/src/router_test.ts

@@ -193,6 +193,11 @@ Deno.test("pathToPattern", async (t) => {
     ).toEqual(
       "/foo{/:name}?/bar{/:bob}?",
     );
+    expect(
+      pathToPattern("(group)/[[name]]/(group2)/index"),
+    ).toEqual(
+      "/{:name}?",
+    );
   });
 
   await t.step("throws on invalid patterns", () => {