prune event is not triggered when removing the last `import` of the parent module

[hi-ogawa]

Describe the bug

Related #20769, #20768

Even after #20768, the prune event is missed when removing the only import from the parent module since import analysis plugin bails out when es-module-lexer detects imports.length === 0 .

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

Lines 295 to 306 in 2c47acc

	if (
	!imports.length &&
	!(this as unknown as TransformPluginContext)._addedImports
	) {
	importerModule.isSelfAccepting = false
	debug?.(
	`${timeFrom(msAtStart)} ${colors.dim(
	`[no imports] ${prettifyUrl(importer, root)}`,
	)}`,
	)
	return source
	}

The reproduction below uses pkg.pr.new from #20768

Reproduction

https://stackblitz.com/edit/github-oc2husn5?file=src%2Fdep.js

Steps to reproduce

• run pnpm run
• open http://localhost:5173/
  • observe orange text
• comment out import "./test.css" from src/dep.js
  • observe text is still orange
• reload browser
  • observe text is not orange

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 20.19.1 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.8.2 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @vitejs/plugin-react: ^5.0.0 => 5.0.2 
    vite: https://pkg.pr.new/vite@2c47acc => 7.1.5

Used Package Manager

pnpm

Logs

No response

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• The provided reproduction is a minimal reproducible example of the bug.