"error: cannot bind by-move with sub-bindings" when sub-binding is _

[lilyball]

The x@foo construct cannot be used in a match arm if foo contains sub-bindings. This is not surprising. However, when the sub-bindings are actually _, this should be allowed as _ is not a real binding.

Example:

match a {
    x@Some(_) => x,
    None => None
}

Result:

foo.rs:3:8: 3:17 error: cannot bind by-move with sub-bindings
foo.rs:3         x@Some(_) => x,

[lilyball]

I think this is a dupe of #3761.