faulty unification of datalog programs and return types

[JonathanStarup]

I am a bit unsure in which system this error lives, but there are two issues with returning datalog values (and ascriptions).

1) underspecified types are sometimes accepted (distinctPairs do not mention Pair in its type, omiting Fact is not allowed). This also applies to ascriptions.

pub def bug(): List[(Int32, Int32)] =
    query #{Fact(1). Fact(2).} <+> distinctPairs()
    select (x, y) from Pair(x, y)

def distinctPairs(): #{Fact(Int32) | r} =
    #{Pair(x: Int32, y: Int32) :- Fact(x), Fact(y), if x != y.}

2) Incorrect type class handling (This results in an empty list instead of (1,2)::(2,1)::Nil because the condition is always false. The asciption of x or y to Int32 fixes this as shown above)

pub def bug(): List[(Int32, Int32)] =
    query #{Fact(1). Fact(2).} <+> distinctPairs()
    select (x, y) from Pair(x, y)

def distinctPairs(): #{Pair(Int32, Int32), Fact(Int32) | r} =
    #{Pair(x, y) :- Fact(x), Fact(y), if x != y.}

[JonathanStarup]

From @paulbutcher (this compiles)

def foo(): #{ Thingy(String) | s } = #{
    Widget("x").
}

[magnus-madsen]

Fixed in master.