DI: In debug mode, trace a provider failure

[matanlurey]

This used to happen in pre-Angular Dart 2.0, but was never added for code generation.

EDIT as of 2018-08-14 - We still need to cover the view-compiler cases to close this:

• Child directives with dynamic dependencies:

  _CompChild2_0_5 = CompChild2(parentView.injectorGet(import1.A, viewData.parentIndex));

  ... should become ...

  // class _ViewFooComponent
  debugInjectorGet(CompChild2);
  _CompChild2_0_5 = CompChild2(parentView.injectorGet(import1.A, viewData.parentIndex));
  debugInjectorLeave(CompChild2);

• Child directives in embedded templates (or anything that triggers parentView.injectorGet):

  (i.e. figure out what code-paths invoke injectFromViewParentInjector)

• Queries for services that live on child directives that have dynamic dependencies

• Provided services with dynamic dependencies:

  _InjectsMissingService_0_5 = InjectsMissingService(injectorGet(MissingService, viewData.parentIndex));

  ... should become ...

  debugInjectorGet(InjectsMissingService);
  _InjectsMissingService_0_5 = InjectsMissingService(injectorGet(MissingService, viewData.parentIndex));
  debugInjectorLeave(InjectsMissingService);

• Provided services via a FactoryProvider

[matanlurey]

This is a WIP. In early code, it's looking ~OK, but with the following mistakes:

When the ViewCompiler generates code like so:

build() {
  _Foo = new Foo(injectorGet(FooDependency));
}

... it would need to insert trace statements ...

build() {
  debugInjectorEnter(Foo);
  _Foo = new Foo(injectorGet(FooDependency));
  debugInjectorExit(Foo);
}

... if we do that, we should get ~100% feature coverage.

[matanlurey]

We talked offline. This is probably OK, but we'll validate first that:

1. The general feature doesn't disrupt testing and development time noticeably.
2. Adding enter/exit doesn't create too much additional code in a typical large DDC application.

[matanlurey]

The rest of this is very non-trivial. We should review at the weekly about the priority of this.

[matanlurey]

I... think either @hterkelsen or @ferhatb was going to help here.

[matanlurey]

Finishing this feature has been postponed until after V5/Dart 2.

[matanlurey]

Related; this would be much easier with dart-lang/sdk#34141.

Otherwise, we'd need to convert current expressions into 3 statements, which is really hard in some places (for example we don't have a great way of creating unique local variables without just using a global counter of some sort).