File polyfills-legacy should not be in strict mode (Plugin legacy)

[pepa-linha]

Describe the bug

For older browsers with IE 11 support generated file polyfills-legacy.[hash].js should not contain use strict directive, but it does.

It is required by polyfill regenerator-runtime/runtime which contains a comment: This module should not be running in strict mode, ... (https://github.com/facebook/regenerator/blob/main/packages/runtime/runtime.js#L736)

Because the built-in file contains use strict, it will result in an error.

Even if I have set

        rollupOptions: {
            output: {
                strict: false // no strict mode, ... but maybe Rollup is wrong, I am not sure
            }
        },

Reproduction

https://stackblitz.com/edit/vite-v5p4en

System Info

System:
    OS: Linux undefined
    CPU: (4) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: Unknown - /bin/jsh
  Binaries:
    Node: 14.16.0 - /usr/local/bin/node
    Yarn: 1.22.10 - /bin/yarn
    npm: 7.17.0 - /bin/npm
  npmPackages:
    @vitejs/plugin-legacy: ^1.6.4 => 1.6.4 
    vite: ^2.6.0 => 2.7.10

Used Package Manager

npm

Logs

No response

Validations

• Follow our Code of Conduct
• 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/vue-next instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[upcccz]

Have you solved it? Or another way?

[pepa-linha]

I solved it in some ugly way that I wrote my own Vite plugin.

import path from 'path'
import MagicString from 'magic-string'

let config

/**
 * Remove "use strict" from code
 * @param {string} code
 * @param {boolean} generateSourceMap
 * @return {{code: string, map: SourceMap|null}}
 */
export const removeUseStrict = (code, generateSourceMap) => {
    const useStrictCode = 'use strict'

    if (code.includes(useStrictCode)) {
        const indexes = [
            ...code.matchAll(useStrictCode),
        ].map(occurrence => occurrence.index)

        if (indexes.length) {
            const ms = new MagicString(code)

            indexes.forEach(index => ms.overwrite(index, index + useStrictCode.length, ''))

            return {
                code: ms.toString(),
                map: generateSourceMap ? ms.generateMap({ hires: true }) : null,
            }
        }
    }

    return {
        code,
        map: null,
    }
}

// Remove 'use strict' from chunks due legacy Chrome browsers
const vitePluginRemoveStrictMode = {
    name: 'remove-strict-mode',
    enforce: 'post',
    apply: 'build',

    configResolved (_config) {
        config = _config
    },

    renderChunk (code, chunk) {
        if (path.extname(chunk.fileName) !== '.js') {
            return null
        }

        const removedUseStrictResult = removeUseStrict(code, config.build.sourcemap !== false)

        if (removedUseStrictResult.code === code) {
            return null
        }

        if (removedUseStrictResult.map !== null) {
            return {
                code: removedUseStrictResult.code,
                map: removedUseStrictResult.map,
            }
        } else {
            return removedUseStrictResult.code
        }
    },
}

export default vitePluginRemoveStrictMode

[upcccz]

I tried too, but because of using transform hook or other hooks, not renderChunk hook , it didn't succeed, so thank you very much for sharing

[upcccz]

sometimes you need to use generateBundle hook, such as dealing with polyfills-legacy.js

[sapphi-red]

I was not able to reproduce it with IE11.

Also regenerator-runtime/runtime states it works if CSP is not enabled. So if CSP is not set, I think it would work.
https://github.com/facebook/regenerator/blob/055b4030219f7cc0af5999ef4431c991697d7ee5/packages/runtime/runtime.js#L739-L748

[bluwy]

The latest plugin-legacy doesn't require adding regenerator-runtime anymore (#8007), so I think this is resolved. https://stackblitz.com/edit/vite-h5edus?file=vite.config.js

There is a separate issue with setting output.strict: false but I think that's a separate issue. Running the repro in Ie11 should be working.