8.3.x ES5 build broken for spread operator on set

[readme42]

🐞 Bug report

Command (mark with an x)

- [x] build

Is this a regression?

No, its broken since the optimized creation of es5 out of es2015 builds were introduced in 8.3. In 8.2.x, when both builds were created on their own, everything was fine.

Description

Since updating angular/cli to 8.3.x it turns our that our ES5 builds are broken - exceptions are thrown during runtime.

What I found out so far:

ES2015 builds are fine.
ES5 builds, created with NG_BUILD_DIFFERENTIAL_FULL=true are fine.
ES5 builds, created without NG_BUILD_DIFFERENTIAL_FULL=true are broken.

It turns out, that the following line creates undefined in es5 builds whereas it creates an array of strings in es2015 builds:

// Make demand ids in day unique
cardDataByDay[ key ] = [ ...new Set(cardDataByDay[ key ]) ];

Happens in any browser in which you load the es5 build.

🔬 Minimal Reproduction / 🔥 Exception or Error

As its quite some effort due to the size to extract it and you maybe already
know what and where to fix it, I will create a test repo when you really need it.
Just drop a comment in this case.

Edit: You can find the repo here: https://github.com/readme42/repro-angular-cli83-es5-15673

🌍 Your Environment

Angular Version:

Angular CLI: 8.3.5
Node: 12.6.0
OS: darwin x64
Angular: 8.2.7
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... platform-server, router

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.803.2
@angular-devkit/build-angular     0.803.2
@angular-devkit/build-optimizer   0.803.2
@angular-devkit/build-webpack     0.803.2
@angular-devkit/core              8.3.2
@angular-devkit/schematics        8.3.5
@angular/cdk                      8.2.1
@angular/cli                      8.3.5
@angular/material                 8.2.1
@ngtools/webpack                  8.3.2
@schematics/angular               8.3.5
@schematics/update                0.803.5
rxjs                              6.5.2
typescript                        3.4.5
webpack                           4.39.2

[alan-agius4]

@readme42, can you please provide the full code snippet that is needed to generate the error?

Thanks.

[readme42]

@alan-agius4 sure - will deliver in the next hours.

[readme42]

@alan-agius4 Here we go.

You can find the repo here: https://github.com/readme42/repro-angular-cli83-es5-15673

Just clone it and run npm start

The ES2015 build shows:

 {
  "shouldContain1234": [
    1,
    2,
    3,
    4
  ],
  "shouldContain567": [
    5,
    6,
    7
  ]
} 

Ths ES5 build shows:

 {
  "shouldContain1234": [
    {}
  ],
  "shouldContain567": [
    {}
  ]
} 

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