[SR-1446] Nested generics

[hartbit]

Previous ID	SR-1446
Radar	rdar://problem/18869049
Original Reporter	@hartbit
Type	Improvement
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Improvement
Assignee	@slavapestov
Priority	Medium

md5: ccb73507bfc3507848f41ef27acd8d6e

Issue Description:

From the Generics Manifesto:

Currently, a generic type cannot be nested within another generic type, e.g.

struct X<T> {
  struct Y<U> { }  // currently ill-formed, but should be possible
}

There isn't much to say about this: the compiler simply needs to be improved to handle nested generics throughout.

[slavapestov]

#5600