fix: inject __vite__mapDeps code before sourcemap file comment

[hi-ogawa]

Description

• Closes Source maps broken due to injected __vite__mapDeps function after sourceMappingURL #15338

#14550 introduced __vite__mapDeps runtime function, which is appended to the chunk output during generateBundle hooks. Rollup's chunk already includes //# sourceMappingURL= comment at this point, thus MagicString.append would inject the code after such comment.

This PR fixes this issue by using MagicString.appendRight to inject right before the sourcemap comment if found.

Note that the issue manifested when sourcemap: true (i.e. separate sourcemap file) but not when sourcemap: "inline" since the comment was re-appended in inline case:

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

Lines 686 to 691 in 0cd4f82

	if (config.build.sourcemap === 'inline') {
	chunk.code = chunk.code.replace(
	convertSourceMap.mapFileCommentRegex,
	'',
	)
	chunk.code += `\n//# sourceMappingURL=${genSourceMapUrl(map)}`

While testing on browsers by previewing playground/js-sourcemap locally, I found that //# sourceMappingURL comment appearing before __vite__mapDeps seems to be actually fine (at least for Chrome). So, I'm a little worried that the cause of the original issue might be something different. I'll ask for the further detail in the issue.

Here is what I tested (where both "before" and "after" look working however):

pnpm -C playground/js-sourcemap build
pnpm -C playground/js-sourcemap preview

Screenshots

• before

• after

Additional context

A few related PRs I looked up while attempting this fix:

• perf: reduce preload marker markup size #14550
• fix: output combined sourcemap in importAnalysisBuild plugin #12642

---

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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[bluwy]

Looks great! Thanks for the fix.

While testing on browsers by previewing playground/js-sourcemap locally, I found that //# sourceMappingURL comment appearing before __vite__mapDeps seems to be actually fine (at least for Chrome). So, I'm a little worried that the cause of the original issue might be something different. I'll ask for the further detail in the issue.

I've seen other toolings before that mandated sourcemap comments to always come last, so I think it make sense to fix this still.

[sapphi-red]

The spec says the comment should be at the end, so I think it's a valid fix, too.

The generated code may include a line at the end of the source
https://github.com/tc39/source-map-spec/blob/main/source-map-rev3.md#:~:text=The%20generated%20code%20may%20include%20a%20line%20at%20the%20end%20of%20the%20source%2C%20with%20the%20following%20form%3A

[maximilianschmid]

@hi-ogawa works great, thanks!