'extern mod foo(name = "bar")' is not equivalent to 'extern mod foo = "bar"'

[tautologico]

I'm trying to tackle #9543 but under the impression that 'extern mod foo(name = "bar")' should be equivalent to 'extern mod foo = "bar"'. After trying to change occurrences of the first form, I noticed rustc does not treat them equally. A minimal test shows this easily:

// world.rs
#[link(name = "world", vers="1.0")];
pub fn explore() -> &str { "world" }

This is used by

// main.rs
extern mod w(name = "world");
fn main() {
    println("hello " + w::explore());
}

And it all works if I compile world.rs as a lib and then compile main.rs passing -L . to rustc. If I change the first line in main.rs to extern mod w = "world", it does not work ("can't find crate for 'w')".

While trying to find out if the two forms should be equivalent I looked at view items in the manual; by the specification there maybe the two forms are not meant to be equivalent, but I was informed on IRC that this is probably a rustc bug, so I'm filing it.

[tautologico]

After some investigation, I found out that the 'extern mod foo(name="bar")' form creates a view item with attached metaitem having key "name" and value "bar". The 'extern mod foo = "bar"' form creates a view item with two metaitems, one with key "name" and value "bar", and other with key "package_id" and also value "bar". This happens in rustc::metadata::creader, function visit_view_item, and it appends the whole path as package_id and only the filestem as name, but in this case both are equal. So in rustc::metadata::loader, find_library_crate_aux finds the crate to load but metadata_matches requires the "package_id" metaitem to be present in the "bar" crate.

I confirmed this with my above example by adding 'package_id="world"' item in the link attribute above (world.rs), and it worked even with 'extern mod w = "world"' in main.rs.

So this amounts to the "package_id" being mandatory in external crates.