Injector allows binding undefined, provide function does not fail when incorrectly used

[mprobst]

• I'm submitting a ...
• bug report

Current behavior

It's very easy to get incorrect behaviour out of the injector, e.g. by accidentally forgetting to pass an object literal to provide. For example, the following will silently fail and bind undefined to MyFoo.

provide(MyFoo, MyFooImpl)  // should be: {useClass: MyFooImpl}

Expected/desired behavior

This should fail on two levels:

• provide should check its arguments, and if none of the arguments are defined, given an error.
• it should be impossible to bind undefined, and probably also impossible to bind null.

undefined is a common error (some import or property is missing, something went wrong)

Allowing to bind null means the code that gets instantiated by the injector gets a ctor parameter (field, whatever) that does not satisfy the contract the injected code expects; doing anything with it will fail. This means very hard to debug error cases, where once the app is running, much later something somewhere fails. Guice handles this by requiring bindings to be annotated as @Nullable if they should take null, but I think we might as well just disallow it; passing null values long distance through a large software system is prone to create very hard to debug error cases.

[tbosch]

This also happens when using the provider literals, e.g. the following code is wrong as the class is declared after the provider, but this is super hard to debug right now.

let providers = [{provide: SomeClass, useClass: SomeClass}];

class SomeClass {}

/cc @vsavkin

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