missing-copy-implementations warning only triggers on externally-reachable types.

[ben0x539]

example, foo.rs:

#![crate_type = "lib"]
mod inner {
    pub struct Foo {
        pub field: i32
    }
}

pub fn foo() -> inner::Foo {
    inner::Foo { field: 42 }
}

bar.rs:

extern crate foo;

fn main() {
    let f = foo::foo();
    drop(f);
    println!("{}", f.field);
}

foo compiles cleanly, bar doesn't compile because oh no! I've forgotten to make foo::inner::Foo Copyable.

[sfackler]

I believe this is intentional.

[tbu-]

This might be a problem though, if we had a private uint wrapper:

 struct MyPrivateUint(uint);

And use that inside of a public struct:

 pub struct Index { idx: MyPrivateUint };

[steveklabnik]

Triage: this compiles today. Closing.

[tbu-]

What compiles today? The examples give me

bar.rs:6:20: 6:27 error: use of moved value: `f.field` [E0382]
bar.rs:6     println!("{}", f.field);
                            ^~~~~~~
<std macros>:2:25: 2:56 note: in this expansion of format_args!
<std macros>:3:1: 3:54 note: in this expansion of print! (defined in <std macros>)
bar.rs:6:5: 6:29 note: in this expansion of println! (defined in <std macros>)
bar.rs:6:20: 6:27 help: run `rustc --explain E0382` to see a detailed explanation
bar.rs:5:10: 5:11 note: `f` moved here because it has type `foo::inner::Foo`, which is non-copyable
bar.rs:5     drop(f);
                  ^
error: aborting due to previous error

without a missing-copy-implementation in the foo.rs compilation.

[steveklabnik]

Whoops! I don't know what I did wrong, but when I had typed that, the example verbatim compiled. Trying again, I get the same error as you.

I must have screwed up a filename or something.

[petrochenkov]

This is a legitimate bug, rustc_privacy::EmbargoVisitor has a large piece of functionality missing - function return types and other types available through everything except for reexports and type aliases are not marked as reachable. This leads to many kinds of problems for such types.

[petrochenkov]

Fixed by #31641, needs a test.

[topecongiro]

The topmost example still fails. Tested onrustc 1.17.0-nightly (691eba135 2017-03-01) and rustc 1.15.1 (021bd294c 2017-02-08).

[petrochenkov]

@topecongiro
missing_copy_implementations is allow-by-default, you need to explicitly enable it to test this:

#![deny(missing_copy_implementations)]

mod inner {
    pub struct Foo {
        pub field: i32
    }
}

pub fn foo() -> inner::Foo {
    inner::Foo { field: 42 }
}

fn main() {}

Result:

rustc 1.17.0-nightly (b1e31766d 2017-03-03)
error: type could implement `Copy`; consider adding `impl Copy`
 --> <anon>:4:5
  |
4 |       pub struct Foo {
  |  _____^ starting here...
5 | |         pub field: i32
6 | |     }
  | |_____^ ...ending here
  |
note: lint level defined here
 --> <anon>:1:9
  |
1 | #![deny(missing_copy_implementations)]
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^