fix: watch build mode infinite build

[btea]

Description

When executing vite build -w, if build.outDir is an empty string, it will cause an infinite packaging loop.

[sapphi-red]

Why does the rebuild trigger? If I remember correctly, rollup only runs the rebuild when an imported file is changed.

[btea]

When build.outDir is an empty string, the watch will monitor the file changes in the current project's root directory. Each build will add new build files or modify the index.html file, thus triggering a new build, and the cycle repeats.

[sapphi-red]

I think the problem is that the output overwrites the watched file. If I change the output filename, it doesn't happen.
https://stackblitz.com/edit/vitejs-vite-6vjnefzs?file=vite.config.js,index.html,package.json&terminal=build:watch

Setting build.outDir: '' is technically fine and I think we shouldn't disallow doing so. I think it's better to fix the behaivor in rollup. For example, output a warning if the output overwrites a watched path.

[btea]

We do output warning messages. But if it is in watch mode, because it will be triggered repeatedly, it seems meaningless even if the warning message is output, so in this case, I think it is more reasonable to terminate the process.

Do you think it's ok to set output.dir to the default value of dist if it's an empty string?

[sapphi-red]

We do output warning messages. But if it is in watch mode, because it will be triggered repeatedly, it seems meaningless even if the warning message is output, so in this case, I think it is more reasonable to terminate the process.

Rollup can skip the rebuild if the rebuild if the output overwrites the input. Or can even skip the output and show an error. Setting build.outDir: '' is technically fine and I think we shouldn't break that usage.

Do you think it's ok to set output.dir to the default value of dist if it's an empty string?

I don't think it's ok. Because setting build.outDir: '' is fine if you have a different input than index.html and have entryFileNames set so that it's output as a different filename.

[btea]

Rollup can skip the rebuild if the rebuild if the output overwrites the input. Or can even skip the output and show an error. Setting build.outDir: '' is technically fine and I think we shouldn't break that usage.

At present, it seems that the rebuild is not skipped. Is there any configuration required?

[sapphi-red]

At present, it seems that the rebuild is not skipped. Is there any configuration required?

It's not implemented. I mean it's better to fix on rollup side as there's not enough information on Vite side to do so, and the fix would benefit users in rollup as well.

[btea]

Thanks for the detailed response. I will create an issue for rollup.