Cannot create property 'ngIf' on number in Angular 8

🐞 bug report

Affected Package

@angular/core

Is this a regression?

I can’t tell exactly, this app is freshly written in angular 8, but I’ve never encountered such issues in previous versions.

Description

ngIf behaves unexpectedly, I have a complex component which consists of multiple smaller components, but still template reaches up to 70 lines. There I have bindings on every component and at the top of the template I have this code:

<h2>
    <span *ngIf="hasBasicInfo(); else missing">
      {{ form.value[basicInfoFormControlName][nameControlName] }}
    </span>
    <ng-template #missing>MISSING</ng-template>
  </h2>

This works perfectly fine until I changed one of subcomponents, which in template looked like this:

<st-classification-in-frameworks
              [solution]="solution"
              [selectedSegments]="solution.segments"
              (segmentSelectionChange)="updateSolutionOnSegmentSelection($event)"
></st-classification-in-frameworks>

Basically I just deleted [selectedSegments]="solution.segments" like and removed an @Input() in that component. As soon as I do that I get error: Cannot create property 'ngIf' on number 871548 It complains exactly about that ngIf I mentioned above. I believe this is a bug in the core rendering(I am using Ivy), because for some reason instance in setInputsForProperty is evaluated as a number, and not only that, sometimes I am also getting boolean value. This appears to be pretty random, because when I remove else part from that ngIf it works again, or if I move it another place. I don’t see how my code can be wrong to break it. But I also don’t have knowledge of how Ivy works from inside to understand why this happens.

🔬 Minimal Reproduction

Unfortunately I was not able to reproduce this in any other setup, this issue seems to be pretty specific and quite random.

🔥 Exception or Error

core.js:7187 ERROR TypeError: Cannot create property 'ngIf' on number '871548'
    at setInputsForProperty (core.js:13500)
    at elementPropertyInternal (core.js:12390)
    at Module.ɵɵproperty (core.js:16528)
    at SolutionComponent_Template (solution.component.html:3)
    at executeTemplate (core.js:12007)
    at checkView (core.js:13358)
    at componentRefresh (core.js:13122)
    at refreshChildComponents (core.js:11710)
    at refreshDescendantViews (core.js:11616)
    at renderComponentOrTemplate (core.js:11985)

🌍 Your Environment

Angular Version:

Angular CLI: 8.0.0
Node: 10.16.0
OS: darwin x64
Angular: 8.0.0
... animations, cdk, cli, common, compiler, compiler-cli, core
... forms, language-service, platform-browser
... platform-browser-dynamic, router

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.800.0
@angular-devkit/build-angular     0.800.0
@angular-devkit/build-optimizer   0.800.0
@angular-devkit/build-webpack     0.800.0
@angular-devkit/core              8.0.0
@angular-devkit/schematics        8.0.0
@ngtools/webpack                  8.0.0
@schematics/angular               8.0.0
@schematics/update                0.800.0
rxjs                              6.5.2
typescript                        3.4.5
webpack                           4.30.0

Anything else relevant?

One more detail is that the error doesn’t happen on initial load of the component. First time it renders correctly, however if hasBasicInfo returns false, it does not render the missing template. Then I click on something that triggers change detection and that error appears. What is interesting is that it only appears twice(for ngIf and ngIfElse, which I could while trying to debug) with different property and third time it actually runs.

[BlindDespair]

I’ll try to create an app where this would be reproducible when I have time. Hopefully this week.

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