Typechecker - bug in synthesizing types of RetE expressions when assumed return type is T.Pre?

[crusso]

func f(i:Int) : Int { i; }; let d = async { return f(4); };
crashes the compiler:
[crusso@LAPTOP-CT4C97Q0 async]$ asc -r repro.as
prelude:34.26-34.38: internal error, File "typing.ml", line 590, characters 2-8: Assertion failed

Last environment:
abs = func
ignore = func
print = func
printInt = func
range = class
revrange = class

Raised at file "typing.ml", line 590, characters 2-21
Called from file "typing.ml", line 521, characters 8-28
Called from file "typing.ml", line 302, characters 10-28
Called from file "typing.ml", line 290, characters 13-36
Called from file "typing.ml", line 955, characters 4-21
Called from file "typing.ml", line 940, characters 10-59
Called from file "typing.ml", line 430, characters 24-51
Called from file "typing.ml", line 302, characters 10-28
Called from file "typing.ml", line 290, characters 13-36
Called from file "typing.ml", line 529, characters 12-31
Called from file "typing.ml", line 302, characters 10-28
Called from file "typing.ml", line 290, characters 13-36
Called from file "typing.ml", line 957, characters 31-50
Called from file "typing.ml", line 1040, characters 16-42
Called from file "typing.ml", line 996, characters 2-56
Called from file "pipeline.ml", line 134, characters 43-70
Called from file "pipeline.ml", line 105, characters 37-52
Called from file "pipeline.ml", line 128, characters 10-41
Called from file "pipeline.ml", line 166, characters 8-23
Called from file "pipeline.ml", line 228, characters 15-33
Called from file "main.ml", line 56, characters 38-65
Called from file "main.ml", line 73, characters 4-23
[crusso@LAPTOP-CT4C97Q0 async]$

[rossberg]

Fixed.