[Bug]: devServer's option true won't automatically apply HMR plugin

[Lancernix]

System Info

System:
OS: macOS 15.2
CPU: (8) arm64 Apple M1
Memory: 105.83 MB / 16.00 GB
Shell: 5.9 - /bin/zsh
Binaries:
Node: 20.18.0 - ~/.nvm/versions/node/v20.18.0/bin/node
Yarn: 1.22.19 - /usr/local/bin/yarn
npm: 10.8.2 - ~/.nvm/versions/node/v20.18.0/bin/npm
pnpm: 8.15.8 - /usr/local/bin/pnpm
Browsers:
Chrome: 134.0.6998.46
Safari: 18.2
npmPackages:
@rspack/cli: ^1.2.8 => 1.2.8
@rspack/core: ^1.2.8 => 1.2.8
@rspack/plugin-react-refresh: ^1.0.1 => 1.0.1

Details

In Webpack5, setting devServer.hot to true will automatically apply HMR plugin.

But in Rspack, setting devServer.hot to true doesn't seem to work, new HotModuleReplacementPlugin() must be added to plugins option to make HMR work properly. However this will result in a warning log: <w> [webpack-dev-server] "hot: true" automatically applies HMR plugin, you don't have to add it manually to your webpack configuration.

The behavior should be consistent, it seems to be a bug.

Reproduce link

No response

Reproduce Steps

1、set devServer.hot to true
2、check if HMR is working
3、add HMR plugin
4、check if HMR is working
5、see dev-server log

[LingyuCoder]

I tried to create a repro, but got the same warning in both rspack-dev-server (pnpm run dev) and webpack-dev-server (pnpm run devw). The class of rspack-dev-server directly inherits from webpack-dev-server, so there should be no differences.

Since the logic of adding the plugin only takes effect when options.webSocketServer is enabled (enabled by default), you can debug whether this configuration is enabled in your scenario.

[github-actions]

Hello @Lancernix, sorry we can't investigate the problem further without reproduction demo, please provide a repro demo by forking rspack-repro, or provide a minimal GitHub repository by yourself. Issues labeled by need reproduction will be closed if no activities in 14 days.