rustdoc: json output failure

[klutzy]

$ cat vacant.rs
#[link(name = "vacant")]; #[crate_type = "lib"];

$ rustdoc vacant.rs -w json
task '<unnamed>' failed at 'Rust generated JSON is invalid??',
/path/to/librustdoc/rustdoc.rs:319

Any library with no #[no_std] causes the failure.
This is because rustdoc::clean::Crate contains externs: HashMap<ast::CrateNum, ExternalCrate> so output is like {1: (...), 2: (...)}.

[chris-morgan]

I can't get JSON output to work at all. A truly minimal test case in the current syntax is:

#[crate_id = "foo"];

$ rustdoc -w json foo.rs
task '<main>' failed at 'Rust generated JSON is invalid??', /home/chris/vc/rust/src/librustdoc/lib.rs:338

[emberian]

cc me