CSS Modules doesn't error on missing composes

[privatenumber]

Describe the bug

When composing a class from another file in CSS Modules, an error is not emitted if the class is not found.

This is akin to not erroring when trying to import a missing export from another JS file, and can lead to bugs.

This is fixed by #16018, but wanted to file it for tracking purposes since this seems like a pretty major issue that wasn't reported.

(Originally reported in privatenumber/vite-css-modules#2)

Reproduction

https://stackblitz.com/edit/vitejs-vite-w9i5ct?file=src%2Fstyle.module.css

Steps to reproduce

1. In style.modules.css, observe that large-text is imported from ./utils.module.css
2. In utils.module.css, observe that it's an empty file
3. In the DOM, observe that undefined is passed in as a class:
   

System Info

N/A

Used Package Manager

npm

Logs

No response

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
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• The provided reproduction is a minimal reproducible example of the bug.

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• vitejs-vite-w9i5ct (Open reproduction)