aliasElement not populated on non-function typedef references

[jcollins-g]

@scheglov

Given the following code:

typedef T0 = void;
typedef T1 = Function;
typedef T2<X> = List<X>;
typedef T3<X, Y> = Map<X, Y>;
typedef T4 = void Function();

T0 a;

class C2 {
  T0 b;
  T1 c;
  T2 d(T3 e, T4 f);
}

DartTypes generated for a, b, c, d, and e do not appear to have populated fields for aliasElement/aliasArguments. Only f has these fields populated. I have gone over how dartdoc is finding these, and just looking at the most basic level of inspecting element.type I do not see the fields populated even with the experiment on. For example:

Without this Dartdoc is unable to reconnect the types to their aliases, which leads to lower quality documentation.

[scheglov]

So, we already support aliasElement and aliasArguments for FunctionType.

We can and will support InterfaceType and TypeParameterType.

We cannot currently support dynamic, Never, and void because these types are singletons in the analyzer. This will require much bigger changes.

[jcollins-g]

Of these I think the dynamic / Never / void case is the least interesting. The others though would be helpful to have though not strictly necessary to ship with (hence P2)

[scheglov]

InterfaceType support was added in https://dart-review.googlesource.com/c/sdk/+/190731
TypeParameterType support will be added in https://dart-review.googlesource.com/c/sdk/+/190734

[jcollins-g]

Great! This probably falls to P3 once both of these land as the other cases aren't that useful to actual users IMO.

[scheglov]

https://dart-review.googlesource.com/c/sdk/+/191303 to publish analyzer.

[kevmoo]

@scheglov – is this fixed?