[v6] [Bug]: URI encoded params sometimes fail to match in <Routes>

[thedanwoods]

What version of React Router are you using?

6.0.0-beta.5

Steps to Reproduce

In some circumstances <Routes> or useRoutes is not matching deeper routes when the params are URI encoded.

This seems to be caused by a bug in the new getPathnameStart function. It's using the length of the params to work out where to trim the pathname. But params has already been URI decoded, whereas the pathname has not, so the .length is not reliable.

Repro at https://codesandbox.io/s/happy-villani-nee76?file=/src/App.js. Click on the "Item with id of ::" link and it doesn't render. If you downgrade to 6.0.0-beta.4 it works as expected.

Expected Behavior

In the codesandbox, /items/abc/%3A%3A should render the <SingleItem /> component.

Actual Behavior

It matches /items/abc/%3A and /items/abc/hi, but not /items/abc/%3A%3A.

[mjackson]

Thanks for the report. I'm pretty sure this is a duplicate of #8072, which I'm working on fixing this week. Should be fixed in the next beta release.