Angular component is not compiling with “--prod” option: Object is of type “unknown”

Affected Package

Not sure

Is this a regression?

Not sure

Description

This is a copy-paste from https://stackoverflow.com/questions/59667441/angular-component-is-not-compiling-with-prod-option-object-is-of-type-unknow

I am trying to compile my Angular application for production (“–prod” option) but I get lots of weird errors like:

blah.component.html(15,11): Object is of type ‘unknown’

Template code that produces these errors is following:

<tbody>
<tr *ngFor="let item of items$ | async">
<td>{{item.name}}</td>
<td>{{item.code}}</td>
</tr>
</tbody>

items$ variable defined as following:

public item$: Observable<ListItem[]>;

What I don’t understand is why I am receiving these error messages as almost same code on my private laptop compiles as expected!

I would be appreciated for any help!

UPDATE 1:

Another error, that I haven’t noticed earlier, points to ngFor statement and says:

blah.component.html(14,11): Type ‘ListItem[] | null’ is not assignable to type ‘ListItem[] | Iterable | undefined’.

Why Angular compiler thinks that items$ property can be either array, or null? It is explicitely defined as Observable<ListItem[]>.

When I changed my template as shown below, these error messages dissapeared:

<ng-container *ngIf="items$ | async as tmp">
<tr *ngFor="let item of tmp">
<td>{{item.name}}</td>
...

🔬 Minimal Reproduction

Just create a simple component with ngFor="let item of items$ | async"

🔥 Exception or Error

blah.component.html(14,11): Type ‘ListItem[] | null’ is not assignable to type ‘ListItem[] | Iterable | undefined’.

blah.component.html(15,11): Object is of type ‘unknown’

🌍 Your Environment

Angular Version:

• Angular CLI: 8.3.22
• Angular: 8.2.14
• Node: 11.12.0
• typescript: 3.5.3

Ivy and AOT are enabled.

Anything else relevant?

Similar code compiles as expected on another laptop with same version of Angular packages!

[usarskyy]

@atscott not sure if this is reproducable. As I wrote before, similar code is compiling fine on another laptop. But I will try to create you an example project with same issues.

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