MergeInjector breaks normal Angular DI priority

[msgoloborodov]

angular/src/directives/uiView.ts

Line 326 in 34c0efc

const mergedParentInjector = new MergeInjector(moduleInjector, parentComponentInjector);

[msgoloborodov]

https://angular.io/guide/hierarchical-dependency-injection#resolution-rules
Angular tries to find dependency in ElementInjector tree, if Angular doesn't find the provider in any ElementInjector hierarchies, it goes back to the element where the request originated and looks in the ModuleInjector hierarchy.
But UIView creates component with custom injector MergeInjector which firstly search token in ModuleInjector and then in ElementInjector.
For example, it will return service provided in root ModuleInjector, but it must return service provided in parent component or in lazy module (child module).
I think it should first look in all parents element injectors and only then in moduleInjector.

[msgoloborodov]

PR to fix this issue: #978.

[wawyed]

When is this an issue?

[xfh]

When is this an issue?

I haven't tested the PR yet, but I know at case where MergeInjector causes a problem. In an angular 18 app (dev-mode), lazy-loaded states are not compatible with angular devtools (chrome extension). They crash with the following error:

ASSERTION ERROR: getInjectorParent only support injectors of type R3Injector, NodeInjector, NullInjector
    at throwError (core.mjs:525:9)
    at getInjectorParent (core.mjs:30898:5)
    at getInjectorResolutionPathHelper

As a result, the angular devtools don't load. The app is working fine though. The states are loading as they should.