Require that the RHS of a move be a local variable

[msullivan]

This is a bit trickier than just making sure that it is a path of length 1, since it could also be an object field or (soon) an upvar.

[graydon]

well, an upvar is still an lval of length 1, and .. an obj field should not be de-initializable. I think you're ok still.

[msullivan]

Right. We need to detect those and disallow them.

[marijnh]

Please also see https://github.com/graydon/rust/issues/57 . Also, checking for a path of length one is not the way to go here. Just look up the def of an expr_path and verify that that is the right kind of def.

[msullivan]

Are you sure you meant #57? That doesn't seem related... We still allow moving from an object field, but otherwise get it right, I think?

[marijnh]

No 57 wasn't what I meant. I meant a bug about moving out of temporaries, which I now can't find because github's bug search is somewhat primitive. I'm assigning this to add code to handle obj fields properly.