Legacy plugin breaks async generators

[Pinpickle]

Describe the bug

I recently upgraded from Vite 2.x to Vite 4.x, and I can no longer build my project. I think it's due to plugin-legacy changing the target browsers here:

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

Lines 187 to 192 in 128f09e

	config.build.target = [
	'es2020',
	'edge79',
	'firefox67',
	'chrome64',
	'safari11.1',

This target leads esbuild to think it needs to transpile async generators (which was usually left to babel). When I run build, it throws this error (from transpiling a dependency): Transforming async generator functions to the configured target environment ("chrome64", "edge79", "es2020", "firefox67", "safari11.1" + 2 overrides) is not supported yet

Reproduction

https://stackblitz.com/edit/vitejs-vite-wddogq

Steps to reproduce

Run npm install and then npm run build

System Info

success Install finished in 1.172s


  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: 16.14.2 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 7.17.0 - /usr/local/bin/npm
  npmPackages:
    @vitejs/plugin-legacy: ^3.0.2 => 3.0.2 
    vite: ^4.1.0-beta.1 => 4.1.0-beta.1

Used Package Manager

npm

Logs

Click to expand!

❯ npm run build
$ vite build
vite v4.1.0-beta.1 building for production...
✓ 6 modules transformed.
dist/assets/index-legacy-6515cddc.js      2.17 kB │ gzip: 1.13 kB
dist/assets/polyfills-legacy-40963d34.js  7.92 kB │ gzip: 3.11 kB
[vite:esbuild-transpile] Transform failed with 1 error:
assets/index-!~{001}~.js:61:0: ERROR: Transforming async generator functions to the configured target environment ("chrome64", "edge79", "es2020", "firefox67", "safari11.1" + 2 overrides) is not supported yet

Transforming async generator functions to the configured target environment ("chrome64", "edge79", "es2020", "firefox67", "safari11.1" + 2 overrides) is not supported yet
58 |    asyncGenerator();
59 |  }
60 |  
   |   ^
61 |  async function* asyncGenerator() {
   |  ^
62 |    yield 0;

error during build:
Error: Transform failed with 1 error:
assets/index-!~{001}~.js:61:0: ERROR: Transforming async generator functions to the configured target environment ("chrome64", "edge79", "es2020", "firefox67", "safari11.1" + 2 overrides) is not supported yet
    at failureErrorWithLog (file:///home/projects/vitejs-vite-wddogq/node_modules/esbuild/lib/main.js:1594:15)
    at eval (file:///home/projects/vitejs-vite-wddogq/node_modules/esbuild/lib/main.js:827:29)
    at responseCallbacks.<computed> (file:///home/projects/vitejs-vite-wddogq/node_modules/esbuild/lib/main.js:691:9)
    at handleIncomingPacket (file:///home/projects/vitejs-vite-wddogq/node_modules/esbuild/lib/main.js:746:9)
    at Socket.readFromStdout (file:///home/projects/vitejs-vite-wddogq/node_modules/esbuild/lib/main.js:667:7)
    at EventEmitter.emit (https://vitejsvitewddogq-ogu5.w-corp.staticblitz.com/blitz.685d3c93544a5e80be2c9e6906d68c0f4bd854cc.js:6:155574)
    at addChunk (https://vitejsvitewddogq-ogu5.w-corp.staticblitz.com/blitz.685d3c93544a5e80be2c9e6906d68c0f4bd854cc.js:6:656481)
    at readableAddChunk (https://vitejsvitewddogq-ogu5.w-corp.staticblitz.com/blitz.685d3c93544a5e80be2c9e6906d68c0f4bd854cc.js:6:656185)
    at Readable.push (https://vitejsvitewddogq-ogu5.w-corp.staticblitz.com/blitz.685d3c93544a5e80be2c9e6906d68c0f4bd854cc.js:6:656869)
    at _0x5baa5a.onStreamRead [as onread] (https://vitejsvitewddogq-ogu5.w-corp.staticblitz.com/blitz.685d3c93544a5e80be2c9e6906d68c0f4bd854cc.js:6:783983)
    at Object.emit (https://vitejsvitewddogq-ogu5.w-corp.staticblitz.com/blitz.685d3c93544a5e80be2c9e6906d68c0f4bd854cc.js:8:250102)
    at _0x555c73 (https://vitejsvitewddogq-ogu5.w-corp.staticblitz.com/blitz.685d3c93544a5e80be2c9e6906d68c0f4bd854cc.js:8:251737)
    at Object._0xecd3d [as emit] (https://vitejsvitewddogq-ogu5.w-corp.staticblitz.com/blitz.685d3c93544a5e80be2c9e6906d68c0f4bd854cc.js:8:248385)
    at https://vitejsvitewddogq-ogu5.w-corp.staticblitz.com/blitz.685d3c93544a5e80be2c9e6906d68c0f4bd854cc.js:8:250999
    at Map.forEach (<anonymous>)
    at _0x55861a (https://vitejsvitewddogq-ogu5.w-corp.staticblitz.com/blitz.685d3c93544a5e80be2c9e6906d68c0f4bd854cc.js:8:250970)

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 vuejs/core 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.

[sapphi-red]

Unfortunately this is a current limitation of plugin-legacy. This requires #6922 to be implemented to plugin-legacy or async generator transpilation supported by esbuild (evanw/esbuild#2780)

Closing as a duplicate of #6922.

This target leads esbuild to think it needs to transpile async generators (which was usually left to babel).

Previously async generators were transpiled by babel for legacy build. But wasn't transpiled for modern build. This means when accessing with browsers that supports dynamic import but doesn't support async generators your site didn't work. See #10052 (comment), #10072 for more details.

[sapphi-red]

I noticed that plugin-legacy could transpile async generators with babel for modern build.