[Bug Report] Vue SFC source map is missing when there is no script block

[meteorlxy]

Describe the bug

Create a vue SFC without script block NoSourceMap.vue:

<template>
  <p>The sourcemap if NoSourceMap.vue is missing</p>
</template>

Check the devtools, you'll find that it does not have sourcemap at the end of the transformed file:

Compared with a SFC with non-empty script block:

---

Suspicious Code

vite/packages/plugin-vue/src/main.ts

Lines 159 to 162 in 4e6c26f

	// if the template is inlined into the main module (indicated by the presence
	// of templateMap, we need to concatenate the two source maps.
	let resolvedMap = options.sourceMap ? map : undefined
	if (resolvedMap && templateMap) {

Currently we require both scriptMap (aka map or resolvedMap in above code) and templateMap existing to concat templateMap with scriptMap. If scriptMap is empty, then templateMap will not be used at all.

Related Issue

#2959 is similar with this one, but it was reporting the missing of sourcemap in prod. These two issues are related, and potentially to have a same / similar root cause, but I think they are different.

Reproduction

https://stackblitz.com/edit/vitejs-vite-mseree?file=src/NoSourceMap.vue

System Info

Not related

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 https://github.com/vuejs/core instead.
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• The provided reproduction is a minimal reproducible example of the bug.