Slava Pestov cde493de0d Sema: Support member types in preCheckExpression() ...

This folds member access on types to a TypeExpr if the member
resolves to a nested type.

This allows [Foo.Bar]() to become an ApplyExpr of a TypeExpr,
rather than an ApplyExpr of an array literal; previously,
only [Foo]() worked.

Two cases that are still unsupported:

1) If G is a generic type and T is a generic typealias, then
   G.T<X> cannot be folded to a TypeExpr, because we cannot
   represent a generic typealias with an unbound generic
   parent type. Such lookups remain member lookups, where
   Sema first opens the base type to produce a bound generic
   type G<$T0>, and then resolves the generic typealias
   member on that.

2) If T is a generic parameter and X is an associated type,
   T.X is not folded down to a TypeExpr either.

Fixes <rdar://problem/16849958>.

2017-05-21 18:12:12 -07:00

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