Broken move semantics in decl_macro

[valff]

Move semantics with declarative macros 2.0 are broken. Can copy non-copy types.
Playground

#![feature(decl_macro)]
#![allow(unused_macros)]

#[derive(Debug)]
struct NonCopy(String);

struct Foo {
  x: NonCopy,
}

macro copy($foo:ident) {
  $foo.x
}

macro_rules! copy2 {
  ($foo:ident) => {
    $foo.x
  }
}

fn main() {
  let foo = Foo { x: NonCopy("foo".into()) };
  assert_two_copies(copy!(foo), foo.x);
  // A similar old-style macro will not work:
  //assert_two_copies(copy2!(foo), foo.x);
}

fn assert_two_copies(a: NonCopy, b: NonCopy) {
  println!("Got two copies: {:?}, {:?}", a, b);
}

rustc --version --verbose:

rustc 1.23.0-nightly (63739ab7b 2017-11-21)
binary: rustc
commit-hash: 63739ab7b210c1a8c890c2ea5238a3284877daa3
commit-date: 2017-11-21
host: x86_64-unknown-linux-gnu
release: 1.23.0-nightly
LLVM version: 4.0

[kennytm]

The error is caught when enabling MIR borrow-check (pass -Z borrowck-mir or -Z nll), so this is a HIR borrow-check-only issue.

[petrochenkov]

Probably some fields are compared by name without hygiene adjustments.

[pnkfelix]

(tagging with nll labels just so we remember to look at this case when double checking lexical vs NLL.)

[nikomatsakis]

We should file this under #47366, seems like?

[petrochenkov]

It's very likely this is fixed on my field hygiene branch, I'll check.

[valff]

@nikomatsakis Thanks for the reference. I will make a PR with a test for this bug soon.