Preserve import.meta.hot for library dev builds

[doman412]

Description

I would like a way to preserve import.meta.hot in library builds. I'm building a library that will be used in a project developed with vite and there doesn't seem to be a way to add HMR code to the library itself for use in my other project. Ideally I would be able to build a dev version of the library with HRM code using a config flag or during a vite build --watch process.

Suggested solution

I think a solution similar to this #8090 would work. Currently, as I'm developing this library, I'm using a locally linked version of vite (3.0.0-beta.6) with custom modifications to the define plugin file as a workaround but ideally it would be built into vite. My workaround is basically to delete the replacement when in dev mode but someone with a better understanding of vite internals may have a more robust solution including configs.

my workaround: packages/vite/src/node/plugins/define.ts

if(isBuild && nodeEnv === 'development'){
  delete importMetaFallbackKeys['import.meta.hot']
}

Alternative

No response

Additional context

No response

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[poyoho]

vite build mode will replace import.meta.hot to false. If you want to kept it in your dist file. I think you need some magic to avoid vite analysis.

const importMeta = import.meta
if(importMeta.hot) {
  ....
}

BTW, for vite build I think to replace import.meta.hot to false is acceptable. 🤔

[doman412]

That doesn't seem to work. Removing my local changes from original issue where I delete the replacement key, importMeta only seems to have the url property and no others.

I agree replacing import.meta.hot with false is good behavior for production builds and would like to keep that, so that those blocks are optimized out. But I would also like to create a development build that keeps import.meta.hot in place. That way when I use my library in a vite based project, I can point to that dev build when developing and have vite hook into the library's HMR code.

[bluwy]

One way Vite can allow this is by moving this line:

vite/packages/vite/src/node/plugins/define.ts

Line 54 in 7d810a9

'import.meta.hot': `false`

into importMetaKeys. That way you can use define: { 'import.meta.hot': 'import.meta.hot' } to opt-in to preserving hot code. If that works for you I can set up a PR for it (or you can if you're interested 🙂 )

[kawazoe]

I too would like a feature like this, but for different reasons. I maintain a library that ships a bunch of components and composables. There's also an optional bundle that users can include to integrate with pinia. I wish it would handle HMR automatically for them, but if I can't have a clean way to preserve import.meta.hot in a production build, while also letting their own bundler remove it, I feel like that's just not something I can do.