fix(server): only warn sourcemap in loadTransform when explicitly turned on

[antfu]

Description

We got quite some warnings regarding sourcemap when we never need them, and it seems there is no way to disable it:

This kind of warning is generally useless but quite annoying to the end users. I think it make more sense only to warn when sourcemap is enabled.

Additional context

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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, especially the Pull Request Guidelines.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Update the corresponding documentation if needed.
• Ideally, include relevant tests that fail without this PR but pass with it.

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[patak-dev]

I think config.build.sourcemap only applies during build. Is there actually a way to disable sourcemaps during dev?

[bluwy]

I don't think dev has an option, it's always implied to be enabled. I'm not really sure if we need an option, or use this build option though. It seems like a helpful warning, but if not you could use customLogger to filter it out.

[antfu]

Yeah. But I still think it might be better to maybe have an dev option to disable the warning. CustomLogger would do for Vite users, but it could be hard for the meta framework to do so.

Either way let's fix the upstream issue first: inikulin/parse5#831

[bluwy]

@antfu are you still interested in pushing forward this PR? I had update the warning in #16170 to print the entire error instead, and I usually find actual configuration error that should be fixed instead of hiding.