Which @angular/* package(s) are the source of the bug?

forms

Is this a regression?

No

Description

We rely on _onCollectionChange() to notify its FormGroupDirective to re-bind its FormControlName directives, and FormGroup is smart enough to propagate its _onCollectionChange() callback so that Child FormGroups can notify too. This happens in two scenarios

1. When we first initialize the FormGroup (the constructor calls _setupControl() which binds _onCollectionChange() to the children
2. When we call registerControl (and associated methods)

The problem is with scenario 1: we may seed each child control with a default callback (an empty function) on init, but we don't propagate a new callback when we eventually bind the FormGroup to a FormGroupDirective. The child FormGroups are still working with the 'default' one. Furthermore the api is private so I don't see any way to fix this on the user side.

If we have a scenario where a child form group adds controls dynamically, and some of those controls are FormControlName directives (see stackblitz), then we fail to trigger _updateDOMValue() on the parent FormGroupDirective. The FormControlName directives are left with orphaned form controls.

Ideally, _registerOnCollectionChange() would cascade to its children (or maybe just call _setupControls() again).

Please provide a link to a minimal reproduction of the bug

https://stackblitz.com/edit/stackblitz-starters-iatn8h?file=src%2Fbroken-form.ts

Please provide the exception or error you saw

Please provide the environment you discovered this bug in (run ng version)

Angular CLI: 18.2.0
Node: 20.11.1
Package Manager: yarn 4.4.0
OS: linux x64

Angular: 18.2.0
... animations, cdk, cli, common, compiler, compiler-cli, core
... forms, language-service, material, platform-browser
... platform-browser-dynamic, router

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1802.0
@angular-devkit/build-angular   18.2.0
@angular-devkit/core            18.2.0
@angular-devkit/schematics      18.2.0
@angular/flex-layout            14.0.0-beta.41
@schematics/angular             18.2.0
ng-packagr                      18.2.0
rxjs                            7.8.1
typescript                      5.4.5
zone.js                         0.14.10

Anything else?

No response