[NgTemplateOutlet] _updateExistingContext causes side effects

[konossow]

🐞 bug report

Affected Package

The issue is caused by package @angular/common

Is this a regression?

I don't know, but I'm sure it occurs also in version 9.

Description

1. Prepare a template that has an object passed by $implicit (cannot be a primitive value).
2. Change 2 times context value of ngTemplateOutlet.
3. After second change origin object was changed.

🔬 Minimal Reproduction

https://stackblitz.com/edit/angular-fvm7oz?file=src/app/app.component.html

1. Select 0.
2. Inspect selected item - has changed.
3. Select 1.
4. Inspect selected item - has changed.
5. Inspect contents of contexts array - value at index 0 was replaced with value at index 1.
6. Select 0.
7. Inspect selected item - has not changed.

🔥 Exception or Error

No error is presented, but if objects inside contexts array are freezed (uncomment line 28 and 31) error is shown:

ERROR TypeError: Cannot assign to read only property '$implicit' of object '[object Object]'
    at NgTemplateOutlet._updateExistingContext (ng_template_outlet.ts:104)
    at NgTemplateOutlet.ngOnChanges (ng_template_outlet.ts:68)
    at checkAndUpdateDirectiveInline (provider.ts:213)
    at checkAndUpdateNodeInline (view.ts:440)
    at checkAndUpdateNode (view.ts:400)
    at debugCheckAndUpdateNode (services.ts:435)
    at debugCheckDirectivesFn (services.ts:396)
    at Object.eval [as updateDirectives] (AppComponent.html:6)
    at Object.debugUpdateDirectives [as updateDirectives] (services.ts:390)
    at checkAndUpdateView (view.ts:370)

🌍 Your Environment

Angular Version:

11.0.8

Anything else relevant?
The reason why I use an object in $implicit is that I don't know the structure of object - it's created dynamically. Therefore I cannot separate properties through additional properties.

[JoostK]

Heya, this is a known issue as reported in #24515. There has been recent activity in #40360 to fix this, but it proved to be a breaking change so it needs coordination to land.

I'll close this as a duplicate of #24515; please follow the aforementioned issues for future updates.

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}