Calling platformBrowserDynamic a second time silently ignores extraProviders

[Erikvv]

I'm submitting a...

[x] Bug report

Current behavior

platformBrowserDynamic().bootstrapModule(ModuleOne);

platformBrowserDynamic([
    {
        provide: 'myValue',
        useValue: 'something',
    }
]).bootstrapModule(ModuleTwo)

Both applications are bootstrapped but 'myValue' is not available to ModuleTwo.

You wouldn't write code like this in a single file but it may happen that independent code both calls platformBrowserDynamic().

Expected behavior

Either

• Make the extraProviders available to the bootstrapped module
• Or throw an error saying you cannot call this function twice
• Or throw an error that calling it twice must have the same arguments.

What is the motivation / use case for changing the behavior?

The issue is hard to debug. Existing code can be broken by newly added independent code if that new code calls platformBrowserDynamic() earlier.

Environment

Angular version: 6.1.1
Browser: not browser-specific

[Erikvv]

Source is at

angular/packages/core/src/application_ref.ts

Line 104 in c95437f

return (extraProviders: StaticProvider[] = []) => {

I'm willing to contribute, I'm just not sure what the desired behavior is.

[mhevery]

You can only have one platform injector. So in a way this works as intended. But an error would be useful. PR with error would be accepted.

[trotyl]

@mhevery The real problem should be why is ALLOW_MULTIPLE_PLATFORMS be false for browser. I don't see any technical problem in allowing that.

Moreover, one can have different Realms in the same page, even global variables are not shared in between.

[mhevery]

The idea was that the platform would hold singletons which have resources which are singletons on the browser such as Location URL. You can only have one of those.

[trotyl]

@mhevery But user can still override PlatformLocation token with its own implementation, so it could totally be a normal NgModule provider in BrowserModule. For example, one may have an internal application in a <div> (without <iframe>) for non-SPA page.

The only valid platform internal provider I can see is PLATFORM_INITIALIZER, which cannot be made NgModule level for its execution timing.

[mhevery]

As I said "idea was" but I think there are simpler ways of getting there.

Problem is that if you bootstrap two apps in a single page (rare but possible) than each app would bring its own Location you would have an issue. Hence Platfrom.

going forward we are thinking of ways to remove it....

[Erikvv]

I did find a hacky workaround for the problem. Just swap the injector:

const extraProviders = [
    {
        provide: 'myValue',
        useValue: 'something',
    }
]

const platform = platformBrowserDynamic()

;(platform as any)._injector = Injector.create({
    providers: extraProviders,
    parent: platform.injector,
})

platform.bootstrapModule(MyModule)

Unfortunately this breaks AOT compilation because of angular/angular-cli#8880