Flow Typing Over Type Invariants

[DavePearce]

(See also #937)

The following test (UnionType_Valid_28) fails to type check for reasons unknown:

type Tree is null | Node

type Node is { int data, Tree left, Tree right }
// Data in nodes reachable from left must be below this
where left is Node ==> left.data < data
// Data in nodes reachable from right must be above this
where right is Node ==> right.data > data

...

The error reported is:

UnionType_Valid_28.whiley:7: expected record
where right is Node ==> right.data > data
      ^^^^^
UnionType_Valid_28.whiley:7: expected record
where right is Node ==> right.data > data
      ^^^^^
UnionType_Valid_28.whiley:7: expected record
where right is Node ==> right.data > data
                        ^^^^^

This test case originated from 013_btree