Cannot call tag value constructors for tag type imported from another crate.

[froystig]

Suppose foo.rc is compiled as a shared (library) crate, and looks like:

mod bar;

and that bar.rs looks like:

type baz = tag(a(), b(), c());

When we compile a file that looks like:

use foo;
import foo.bar;

fn main() {
    let bar.baz x = bar.a();   // alternatively bar.b() or bar.c()
}

we are told

Fatal error: exception Failure("internal_check_ext_lval: ident a not found in mod item")

in response to our use of bar.a().

Fix whatever is wrong with tags imported from an external crate.

[froystig]

Here's the post-parse AST for the main file:

import bar = foo.bar
export *;
fn main() -> () {
    let mutable bar.baz x;
    x = bar.a();
}
mod foo {
    export *;
    mod bar {
        export *;
        type baz = rec(uint tag);
    }
}

Looks like DWARF for tag types is emitted incorrectly or parsed incorrectly.

[pcwalton]

In fact, DWARF for tag types isn't parsed at all (see the handling of DW_TAG_structure_type at boot/me/dwarf.ml line 2954).

[pcwalton]

The DWARF is parsed as of commit 88c9759, but the tag constructors still aren't created.

[pcwalton]

This will be fixed when tag types become fully nominal. graydon is working on this right now.

[graydon]

Fixed ages ago.