params encoded with encodeURIComponent incorrectly decoded for relative paths if they contain #

[SangJunBak]

I'm using React Router as a...

library

Reproduction

Version: react-router-dom 6.27.0
Sandbox: https://codesandbox.io/p/devbox/mutable-framework-4l8645-forked-vq3pdx

Steps to reproduce:

1. Go to the sandbox and click nested path with a'bc\d/e#f//g_

2. Notice how we show "whatever - name: "a'bcd/e#f//g_"

3. Click "relative link after surrounding spaces: whatever" which is defined as <Link to="./whatever">. Notice how the URL changes from https://vq3pdx.csb.app/foos/foo/a'bcd%2Fe%23f%2F%2Fg_/whatever to https://vq3pdx.csb.app/foos/foo/a'bcd%2Fe/whatever

System Info

System:
  OS: macOS 15.3.1
  CPU: (10) arm64 Apple M1 Max
  Memory: 1.56 GB / 64.00 GB
  Shell: 5.9 - /bin/zsh
Binaries:
  Node: 18.18.0 - /usr/local/bin/node
  Yarn: 4.3.1 - /opt/homebrew/bin/yarn
  npm: 9.8.1 - /opt/homebrew/bin/npm
  pnpm: 8.13.1 - /opt/homebrew/bin/pnpm
Browsers:
  Brave Browser: 118.1.59.117
  Chrome: 133.0.6943.127
  Edge: 133.0.3065.69
  Safari: 18.3
npmPackages:
  vite: ^6.0.11 => 6.0.11

Used Package Manager

yarn

Expected Behavior

In step 3 of steps to reproduction, the URL should be https://vq3pdx.csb.app/foos/foo/a'bcd%2Fe%23f%2F%2Fg_/whatever

Actual Behavior

The URL becomes https://vq3pdx.csb.app/foos/foo/a'bcd%2Fe/whatever. Interestingly enough, if you remove the hashtag from the URI component a'bc\d/ef//g_, you get the correct behavior

[nklein]

The same problem also occurs for question marks.

[h4ka]

I have the same problem.
when I navigate to /branches/#feature with <Link to="/branches/{encodeURIComponent(branchName)}">
which takes me to /branches/%23feature. Which is fine.
But when onClick={() => navigate("./commits")} I would expect it to take me to /branches/%23feature/commits but instead it takes me to decoded URL - /branches/#feature/commits which breaks the routing