Unexported ifaces should export metadata anyway for cross-crate monomorphisation

[bblum]

Spent too long figuring out an ICE: "'lookup_item: id not found: 51905', /home/bblum/rust/src/rustc/metadata/decoder.rs:96".

Turns out I had defined an iface in libcore/task.rs to use in a polymorphic function. I had exported the function, but not the iface. Then when attempting to compile a program that linked against libcore, this failure arose from type_of() in trans/type_of.rs when trying to #debug-print the type, called from monomorphic_fn() in trans/base.rs.

As a workaround, exporting the iface makes the metadata lookup go through.

Maybe all enums need this treatment too?

[catamorphism]

Offhand it looks like a reachability bug, but I'll investigate.

[catamorphism]

@bblum Do you have a test case for reproducing this?

[catamorphism]

Closing due to lack of test case; reopen if you have one.

[bblum]

foo.rs:

export foo;
iface local_data { }
impl <T> of local_data for @T { }

fn foo<T>(t: @T) -> local_data {
    t as local_data
}

foo.rc:

#[link(name = "foo", vers="0.0")];
#[crate_type = "lib"];

bar.rs:

import foo;
fn main() { foo::foo(@5); }

bar.rc:

use foo;

run rustc foo.rc; rustc -L . bar.rc

The ICE goes away if:

• foo is made to return unit
• foo is not polymorphic

[bblum]

Arguably the above should refuse to compile, because foo has in its signature a nonexported type.

Here is a variation that still crashes:

trait face { fn x() -> int; }
impl <T> of face for @T { fn x() -> int { 5 } }

fn foo<T>(t: @T) -> int {
    (t as face).x()
}

[bblum]

Doesn't seem to happen with enums. This works fine:

export foo;
impl x<T> for face<T> { fn x() -> int { 5 } }
enum face<T> = @T;

fn foo<T>(t: @T) -> int {
    face(t).x()
}

[bblum]

related #2313?

[catamorphism]

Seems like the fix for #2945 should fix this too, but I'll still check.

[bblum]

pretty sure 1528256 fixed this. the bug is gone, anyway.