HaMLet S: exhaustiveness check for record ellipsis

[minoki]

The following program is (correctly) rejected because the pattern is non-exhaustive:

let val { a = SOME f } = { a = SOME (fn x => x) }
in f 1;
   f "x"
end;

But, a slight modification circumvents the exhaustiveness checker and allows the program to compile without a warning:

let val { ... = { a = SOME f } } = { a = SOME (fn x => x) }
in f 1;
   f "x"
end;

The exhaustiveness checker should correctly handle ... pattern.

[rossberg]

Indeed, it seems like I never extended the exhaustiveness check to extensible records. Fixed now, thanks for reporting!