if you forget @Injectable() on a factory, debugging is a torture

[trinarytree]

try to bind something like this:

const Binding(Foo, toFactory: fooFactory)
// Notice how I don't have @Injectable() here, and why should I?
// It's not like the factory itself is injectable.
Foo fooFactory() => new Foo();

here's the completely unhelpful error message I get:

Uncaught Unhandled exception:
The null object does not have a method 'get'.

NoSuchMethodError: method not found: 'get'
Receiver: null
Arguments: [Type: class 'ExceptionHandler']
dart:core-patch/object_patch.dart 42                                      Object._noSuchMethod
dart:core-patch/object_patch.dart 45                                      Object.noSuchMethod
package:angular2/src/core/application_ref.dart 429:45                     ApplicationRef_.bootstrap.<fn>
...

nothing in the remaining stack trace hints at where the problem is.
to figure it out, you have to go to application_ref.dart:429, read a bunch of code to figure
out where the injector is getting set, guess that it's on line 268, set a breakpoint there,
try to run this.injector.resolveAndCreate yourself in the debugger, and extract a slightly more
meaningful stack trace - and i mean slightly. this is what i get:

 type '() => Map' is not a subtype of type 'Type' of 'type'.

type, type of type of type... what??
still no part of the stack trace tells me where the problem is, just that it involves the type Map.
<huge leap of imagination>
now i recall that i recently bound a Map, so i go there.
</huge leap of imagination>
nothing leaps out at me as being wrong.
so i search all over other people's code to see how they do it and see that
some, but not quite all, people put @Injectable() on their factories.
why are those other people who don't put @Injectable() not broken?
answer: they probably are but don't know it yet because their code isn't being exercised.

how about an error message more like this?:
"Injector could not create an instance for injector key because it could not find factory name.
Perhaps you forgot to annotate the factory with @Injectable()?"
of course, if you knew factory name, then why do i need to put an annotation on it?
obviously you found it. so maybe you can only say
"Injector could not create an instance for injector key because it could not find a corresponding factory. Perhaps you forgot to annotate the factory with @Injectable()?".
but at this point, i have to wonder how you found my binding. it has the factory inside it.
so let's suppose that you can't find my binding.
ok, then, how the heck did you find my binding just because i put @Injectable on a factory that it refers to?!

so basically, i have no idea what twisted things angular is doing here, but the error message needs improvement or better yet, get rid of the seemingly senseless requirement to add @Injectable() on every factory method. the boilerplate is bad enough due to forbidding anonymous factory methods.

[vicb]

Could you try const Binding(Foo, toFactory: fooFactory, deps: []).

@Injectable() is not required when you bind to a factory. I suspect that the real issue is that as there is no deps specified, the DI will try to get them using reflection info which are not present.

(The error message needs to be updated anyways)

[chalin]

FYI, I hit this issue while working on the angular.io Dart "Http Client" chapter. Specifically in main.dart:

void main() {
  bootstrap(AppComponent, const [
    // in-memory web api provider
    const Provider(BrowserClient,
        useFactory: HttpClientBackendServiceFactory, deps: const [])
  ]);
}

Adding deps as @vicb suggested seemed to be the work around to make DI happy. Without it, pub build reports no problems, but when I run in Dartium, from the console I get:

Exception: Cannot find reflection information on HttpClientBackendServiceFactory

cc @kwalrath @thso

[kwalrath]

We should cover this somewhere in the docs (maybe a troubleshooting doc?), but it would of course be better if there were a helpful error message early in the dev process.

[pkozlowski-opensource]

We've got TS errors covered now and Dart specific errors are obsolete. Closing this one.

[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.}