The crate store does not deduplicate used crates

[brson]

If you have code that links the same crate multiple times, the metadata loader may record several copies of the same crate in its crate list, e.g.

extern mod std(vers = "0.4");
extern std;

This could have potentially bad effects. It has already resulted a mysterious situation that caused all the crate hashes to change because of a spurious 'use'. I can imagine it also could cause types to not resolve if referenced from different mount points.

I believe that the metadata loader does make some effort to do this but it isn't sufficient.

[pnkfelix]

Bug triage 2013jun24. I tried to construct an example where linking to the same crate multiple times would cause the types to not resolve, but I did not encounter any examples of such. Still, it would be good to fix this bug.

[huonw]

Triage: I think this may be fixed.

#[no_uv];

#[cfg(extra_crate)]
extern mod std;

fn main() {}

$ RUST_LOG=rustc::metadata::creader rustc --cfg extra_crate 3474.rs
resolving extern mod stmt. ident: @"std" path_opt: None
resolving deps of external crate
resolved crates:
cnum: 1u32
span: syntax::codemap::Span{lo: syntax::codemap::BytePos(0u32), hi: syntax::codemap::BytePos(0u32), expn_info: None}
hash: @"04ff901ef9eb93b7ed8d17b7ddf76fa8eb8b4c7295ad21af7133790d77381330"

and the output is the same without --cfg extra_crate. The above is full dump of the crate_cache list, clearly std doesn't appear twice (Without the no_uv there are two, rustuv and std).