inline structural/alias invocations even with generic arguments, broken

[metagn]

In:

type
  NodeObj[T] = object
    x: Node[T]
  Node[T] = ref NodeObj[T]

first SemcheckTopLevelSyms will save the untyped AST of the types to their symbols, however they will not define typevars or look them up in the body. This means when NodeObj is being semchecked, attempting to inline Node[T] by instantiating it will not work because there will be no typevars to replace.

This is a general problem for forwarded generic types:

type
  Foo[T] = object
    x: Bar[int]
  Bar[T] = object

A solution might be to define the typevars in the SemcheckTopLevelSyms pass and use an untyped prepass on the body so that they can be instantiated. But this is not done yet as an untyped prepass is not implemented.

The original reason for this PR was that the Node[T]() object constructor syntax/dotfields etc in generics don't work without it, but there is another solution which is just recursively skipping ref/invocations.

[metagn]

Can reopen when ready