Re: [BUGS] Failure to coerce unknown type to specific type

Hello, I think this is a bug.

The core of this problem is that coerce_type() fails for Var of
type UNKNOWNOID.

The comment for the function says that,

> * The caller should already have determined that the coercion is possible;
> * see can_coerce_type.

But can_coerce_type() should say it's possible to convert from
unknown to any type as it doesn't see the target node type. I
think this as an inconsistency between can_coerce_type and
coerce_type. So making this consistent would be right way.

Concerning only this issue, putting on-the-fly conversion for
unkown nonconstant as attached patch worked for me. I'm not so
confident on this, though..