Broken support for async/await

[krojew]

🐞 bug report

Affected Package

@angular-devkit/build-angular > 0.802.2

Is this a regression?

yes

Description

When building with target es2017 using @angular-devkit/build-angular 0.802.2, async/await functions work without problems. When using higher versions, they are surrounded with regeneratorRuntime, which is undefined. When changing target to es2015, async/await gets transformed to yield.

🔬 Minimal Reproduction

Build https://angular-issue-repro2-vbhzdn.stackblitz.io with described cases.

🔥 Exception or Error

Uncaught ReferenceError: regeneratorRuntime is not defined

🌍 Your Environment

Angular Version:

Angular CLI: 8.3.4
Node: 12.10.0
OS: linux x64
Angular: 8.2.6
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router, service-worker

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.803.4
@angular-devkit/build-angular     0.803.4
@angular-devkit/build-optimizer   0.803.4
@angular-devkit/build-webpack     0.803.4
@angular-devkit/core              8.3.4
@angular-devkit/schematics        8.3.4
@angular/cdk                      8.2.0
@angular/cli                      8.3.4
@angular/pwa                      0.803.4
@ngtools/webpack                  8.3.4
@schematics/angular               8.3.4
@schematics/update                0.803.4
rxjs                              6.5.3
typescript                        3.5.3
webpack                           4.39.2

[clydin]

zone.js does not support native async/await. Using anything above ES2015 for TypeScript is not recommended and will most likely cause failures or unexpected behavior at runtime.

The set of browsers that fully support ES2017 and that support module scripts are also not identical. Depending on the features used within the application, the application may not work on newer browsers.

[krojew]

Can you give concrete reasons why using anything above es2015 is not recommended for TS? It does officially support every target above.

[devoto13]

Ref: angular/angular#31730