Missing optional param when using pathless layoutes

[JohanDavidsson]

Which project does this relate to?

Router

Describe the bug

I have two pathless layoutes. Both have a optional language param route in them. When one of them gets matched the param is missing from useParams.

Your Example Website or App

https://stackblitz.com/edit/github-fkabbqxu?file=src%2Froutes%2F__root.tsx

Steps to Reproduce the Bug or Issue

1. Go to link "/sv (first pathless)"
2. See useParams returns nothing, should return {language: "sv"}

Expected behavior

useParams should, if i'm not mistaking, return {language: "sv"}, but returns nothing.

Screenshots or Videos

No response

Platform

• Router / Start Version: 1.139.12.
• OS: macOS
• Browser: Chrome
• Browser Version: 142
• Bundler: Vite
• Bundler Version: 7.1.2

Additional context

Stopped working when updating from 1.131.36 to 1.139.12. Worked as expected in 1.131.36

[Sheraff]

Interesting issue you got there.

First of all, I'm not really sure how this happened, but there is a "hidden" route in the stackblitz you linked, that I do not see in the files, but that does get generated by the dev server: /{-$year}/{-$month}/{-$day}. It can be seen by looking in the routeTree.gen.ts.

Trying to make a minimal reproduction of your issue in unit tests directly in the core of the repo (packages/router-core) I get a weird result.

describe('edge-cases', () => {
  it('#6012: optional index at root with param extraction', () => {
    const tree = {
      "id": "__root__",
      "fullPath": "/",
      "path": "/",
      "isRoot": true,
      "options": {},
      "children": [
        {
          "id": "/{-$year}/{-$month}/{-$day}",
          "fullPath": "/{-$year}/{-$month}/{-$day}",
          "path": "{-$year}/{-$month}/{-$day}",
          "isRoot": false,
          "options": {}
        },
        {
          "id": "/_pathless/{-$language}/",
          "fullPath": "/{-$language}/",
          "path": "{-$language}/",
          "isRoot": false,
          "options": {}
        }
      ]
    }
    const { processedTree } = processRouteTree(tree)
    const result = findRouteMatch(`/sv`, processedTree)
    expect(result?.route.id).toBe('/_pathless/{-$language}/')
    expect(result?.params).toEqual({ language: 'sv' })
  })
})

This is what we would want to happen, but what I get when running this is:

AssertionError: expected { year: 'sv' } to deeply equal { language: 'sv' }

- Expected
+ Received

  {
-   "language": "sv",
+   "year": "sv",
  }

Meaning it matches /_pathless/{-$language}/ as a route, but extracts { "year": "sv" } as the params... This is extremely weird, and this is not even what is shown in stackblitz because there we observe {} as the params.

[JohanDavidsson]

@Sheraff Sorry for messing up the StackBlitz somehow, I went back and forth trying to reproduce a minimal example of the error I was seeing in my much more complex setup. Anyway, I just wanted to say a huge thank you for the fix! I reported a edge-case bug, and two hours later there’s a fix available on npm. That’s amazing!