feat(plugin-legacy): add option to output only legacy builds

[amirkian007]

Description

fix #9050

Additional context

i tried to remove the modern chunks before the transformIndexHtml happens but ended up breaking the generated html file .

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[sapphi-red]

Thanks for the PR!

i tried to remove the modern chunks before the transformIndexHtml happens but ended up breaking the generated html file .

Would you expand on this?

BTW lint is failing because of a different reason. Merging main branch will fix this.

[amirkian007]

Thanks for the PR!

i tried to remove the modern chunks before the transformIndexHtml happens but ended up breaking the generated html file .

Would you expand on this?

BTW lint is failing because of a different reason. Merging main branch will fix this.

reproduction
so basically the logical method is to remove any modern chunk before its entry(<script/>) is added to html. i tried some solutions like adding a new plugin with {enforce :pre} to delete chunks ,or during another plugin like legacyGenerateBundlePlugin, but somehow this will result in a html file without any <script/> or <link /> (for css).not sure if it's a bug or not ,i provided a reproduction for you. i believe the safest method is probably the one i provided in this PR, what's your opinion?... Thanks.

[sapphi-red]

i provided a reproduction for you

It seems this was not working because transformIndexHtml is called only with legacy chunk while the original hook expects to be called with legacy and modern chunk.

what's your opinion?

Maybe we could completely skip modern chunk generation by removing modern chunk from rollupOptions.output?

[zhangchenna]

after using import.meta error

[amirkian007]

Maybe we could completely skip modern chunk generation by removing modern chunk from rollupOptions.output?

@sapphi-red We could manipulate output options using outputOptions() hook, but i don't think that works because options like output.chunkFileNames and output.entryFileNames have default values and i couldn't find any options that would skip modern chunk creation. same thing for rollupOptions.input

[sapphi-red]

We are appending the legacy output option here. I wonder if it is possible to replace rollupOptions.output here instead of using outputOptions hook.

vite/packages/plugin-legacy/src/index.ts

Lines 287 to 305 in ef52db1

	const createLegacyOutput = (
	options: OutputOptions = {}
	): OutputOptions => {
	return {
	...options,
	format: 'system',
	entryFileNames: getLegacyOutputFileName(options.entryFileNames),
	chunkFileNames: getLegacyOutputFileName(options.chunkFileNames)
	}
	}
	const { rollupOptions } = config.build
	const { output } = rollupOptions
	if (Array.isArray(output)) {
	rollupOptions.output = [...output.map(createLegacyOutput), ...output]
	} else {
	rollupOptions.output = [createLegacyOutput(output), output || {}]
	}
	},

[amirkian007]

@sapphi-red I tested it and it is not possible to replace rollupOptions.output(the one that is for modern chunks => [name].[hash].js) from there...

[sapphi-red]

Closing as #10139 implements in a more performant way.