feat: export constants from @vite/plugin-legacy

[dishuostec]

Description

This PR does not changed anything, it just exports some constants.

Additional context

I'm trying to integrate @vitejs/plugin-legacy into SvelteKit.

SvelteKit has an independent logic of HTML rendering. It seems that SvelteKit could not simply use @vitejs/plugin-legacy to directly modify html. With these constants, it is able to do two things:

1. Find with file are polyfills generated by plugin.

2. Generates script tags like this:

import * as constants from '@vitejs/plugin-legacy/constants';

const {
	dynamicFallbackInlineCode,
	safari10NoModuleFix,
	legacyPolyfillId,
	legacyEntryId,
	// systemJSInlineCode,
} = constants;

const systemJSInlineCode = `(function(s,i){i(s.getAttribute('data-src')).then(function(m){window._sveltekit_init(m.start,i,s.getAttribute('data-nodes'))})})(document.getElementById('${legacyEntryId}'),function(m){return System.import(m)});`;

/**
 * @param {{
 *   legacy_polyfill_asset?: string;
 *   entry_file: string;
 *   branch: any[];
 *   get_entry: (entry:string)=>string;
 * }} config
 * @return {string[]}
 */
export function render_script_tags({ legacy_polyfill_asset, get_entry, entry_file, branch }) {
	const legacyEntryFilename = get_entry(entry_file);

	const scripts = [];

	// inject dynamic import fallback entry
	if (legacy_polyfill_asset) {
		scripts.push(`<script type="module">${dynamicFallbackInlineCode}</script>`);
	}

	// inject Safari 10 nomodule fix
	if (legacyEntryFilename) {
		scripts.push(`<script nomodule>${safari10NoModuleFix}</script>`);
	}

	// inject legacy polyfills
	if (legacy_polyfill_asset) {
		scripts.push(
			`<script nomodule id="${legacyPolyfillId}" src="${legacy_polyfill_asset}"></script>`
		);
	}

	// inject legacy entry
	if (legacyEntryFilename) {
		scripts.push(
			`<script nomodule id="${legacyEntryId}" data-src="${legacyEntryFilename}" data-nodes="${(
				branch || []
			)
				.map(({ node }) => get_entry(node.entry))
				.join(',')}">${systemJSInlineCode}</script>`
		);
	}

	return scripts;
}

[bluwy]

Related PRs from SvelteKit: sveltejs/kit#2953 and sveltejs/kit#2745

[shynome]

sveltekit needs @vite/plugin-legacy, hope this pr can be merged as soon as possible

[bluwy]

The PR title needs to be semantic, e.g. feat: export constants from plugin-legacy. Code-wise, I'm probably not qualified to review the overall benefits of this, but if it's something the team is comfortable of exporting, I think we should export them from index.js instead? I don't see much benefits having them at constants.js

[sapphi-red]

It seems this is same with #4045.

[bluwy]

It seems this is same with #4045.

Yeah it seems like so. Let's move the discussion over to #4045 then as there's more info there. Thanks for the PR and example usecase!