A move-through-deref is confusing rustc somehow

[jonnydee]

The compiler complains with an error but the code is supposed to be accepted:

I tried this code:

#[derive(Debug)]
enum BinTree {
    Node {
        lhs: Box<BinTree>,
        rhs: Box<BinTree>,
    },
    Leaf,
}

fn print_tree(bt: BinTree) {
    println!("{:?}", bt);
}

fn main() {
    let t = Box::new(BinTree::Node {
        lhs: Box::new(BinTree::Leaf),
        rhs: Box::new(BinTree::Leaf),
    });

    match *t {
        BinTree::Node { lhs: l, rhs: r } => print_tree(*l),
        _ => println!("Other"),
    }
}

I expected to see this happen:

The compiler should accept this code as it does when I change it to:

let t = *t; match t { ... }

The compiler also has no problem, if I change the match arm to:

BinTree::Node { lhs: l, .. } => print_tree(*l), // Note the '..' here.

Instead, this happened:

The compiler rejects this code with the following error message:

rustc 1.15.1 (021bd294c 2017-02-08)
error[E0382]: use of collaterally moved value: `(t:BinTree::Node).rhs`
  --> <anon>:21:38
   |
21 |         BinTree::Node { lhs: l, rhs: r } => print_tree(*l),
   |                              -       ^ value used here after move
   |                              |
   |                              value moved here
   |
   = note: move occurs because `(t:BinTree::Node).lhs` has type `Box<BinTree>`, which does not implement the `Copy` trait

error: aborting due to previous error

Meta

rustc --version --verbose:

rustc 1.15.0 (10893a9a3 2017-01-19)
binary: rustc
commit-hash: 10893a9a349cdd423f2490a6984acb5b3b7c8046
commit-date: 2017-01-19
host: x86_64-apple-darwin
release: 1.15.0
LLVM version: 3.9

[jonnydee]

A very nice guy on the IRC pointed out that this bug seems to be related to #30104, #34859 and #30564. So I close it again. Sorry for any inconvenience.

Using the following code works:

match { *t } { ... } // Note the use of curly braces here.