fix: handle non-existing files in sourcemap

[HerringtonDarkholme]

Description

If a source map contains a file in source section without uploading the referenced file, Vite will complain about ENOENT.
This fix makes Vite more lenient with npm ecosystem's misdemeanor.

Additional context

When a npm package's source map has a source field, Vite will resolve the referenced file. However, not all packages will upload the source to npm registry, which makes such error. For example, the package compute-scroll-into-view does have such sources field.

And vite throws an error.

Instead of throwing an error, this fix makes Vite ignore the missing source file.
To make the output less noisy and make the build successful, a comment is added for possible suggestion in the emitted source map. This supersedes #2904.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
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• Ideally, include relevant tests that fail without this PR but pass with it.

[aleclarson]

Thanks, but I'd rather the devtools show the compiled code instead of a mostly useless comment.

I've updated #2904 to warn just once per sourcemap instead of throwing an error. It uses logger.warnOnce to ensure the same warning is never printed twice. You can even use DEBUG="vite:sourcemap" to log the list of missing sources after each warning. Let me know if that approach is good enough for you.

[HerringtonDarkholme]

Thanks.

Thanks, but I'd rather the devtools show the compiled code instead of a mostly useless comment.

But I'd rather argue warning in devtools is, well, equally useless and a debugging log is too hard to find after a flag.(finding th flag is not discoverable unless one reads the source).

But whatever, no blocking the build is enough for most devs and hope #2904 gets merged soon.