Type error with cross-crate polymorphism

[honzasp]

Hi,

I have an enum containing some polymorphic structs:

mod picture {
  pub enum Picture {
    Picture8(~Pixels<u8>),
    Picture16(~Pixels<u16>),
  }

  pub struct Pixels<S>(~PixelsInfo<S>, ~[S]);
  pub struct PixelsInfo<S> {
    transparent: Option<S>,
    background: Option<S>,
  }
}

which is used as:

let pixels_info: ~picture::PixelsInfo<u8> = ~picture::PixelsInfo {
      transparent: Some(20),
      background: None,
    };

It works fine when it is in the same file as the code that uses it, but when I place it in a different crate, I got strange type errors (shortened):

error: mismatched types: expected `~picture::PixelsInfo<'a>` but found `~picture::PixelsInfo<u8>` (expected type parameter but found u8)
error: mismatched types: expected `~['a]` but found `~[u8]` (expected type parameter but found u8)
error: mismatched types: expected `~picture::Pixels<u8>` but found `~picture::Pixels<'a>` (expected u8 but found type parameter)

(the full source code is at https://gist.github.com/honzasp/5693895 -- type make to see it in action)

The error message is also confusing a bit, because the 'a ("expected ~picture::Pixels<u8> but found ~picture::Pixels<'a>) looks like a region bound (&'a foo), but seems to be a type metavariable (but I might be wrong, as I don't really understand the details of the compiler).

[huonw]

This looks like the same bug as #7899; closing in favour of that one as it has the "modern" error message and a smaller testcase.