Compilation / linking error: Undefined symbols for architecture x86_64

Question

My Rust compiler version is:

$ rustc --version
rustc 1.0.0-nightly (3e4be02b8 2015-03-13) (built 2015-03-13)

My Cargo version is:

$ cargo --version
cargo 0.0.1-pre-nightly (66849de 2015-03-10) (built 2015-03-11)

I was happily coding my rust project when I got this compilation error:

    $ cargo build --verbose
       Fresh log v0.2.5
       Fresh rustc-serialize v0.3.6
       Fresh libc v0.1.3
       Fresh rand v0.1.4
       Fresh uuid v0.1.11
   Compiling rexchange v0.0.1 (file:///Users/sam/dev/rexchange)
     Running `rustc src/main.rs --crate-name rexchange --crate-type bin -g --out-dir /Users/sam/dev/rexchange/target/debug --emit=dep-info,link -L dependency=/Users/sam/dev/rexchange/target/debug -L dependency=/Users/sam/dev/rexchange/target/debug/deps --extern uuid=/Users/sam/dev/rexchange/target/debug/deps/libuuid-f80da2be6e37bdc9.rlib --extern rexchange=/Users/sam/dev/rexchange/target/debug/librexchange-436e10ddf2e26a6f.rlib`
error: linking with `cc` failed: exit code: 1
note: "cc" "-m64" "-L" "/usr/local/lib/rustlib/x86_64-apple-darwin/lib" "-o" "/Users/sam/dev/rexchange/target/debug/rexchange" "/Users/sam/dev/rexchange/target/debug/rexchange.o" "-Wl,-force_load,/usr/local/lib/rustlib/x86_64-apple-darwin/lib/libmorestack.a" "-Wl,-dead_strip" "-nodefaultlibs" "/Users/sam/dev/rexchange/target/debug/librexchange-436e10ddf2e26a6f.rlib" "/Users/sam/dev/rexchange/target/debug/deps/libuuid-f80da2be6e37bdc9.rlib" "/Users/sam/dev/rexchange/target/debug/deps/librustc-serialize-6bb45c0d7c639d54.rlib" "/Users/sam/dev/rexchange/target/debug/deps/librand-6dfe5258ada5ebf2.rlib" "/Users/sam/dev/rexchange/target/debug/deps/liblibc-2a692f33a70517c8.rlib" "/usr/local/lib/rustlib/x86_64-apple-darwin/lib/libstd-4e7c5e5c.rlib" "/usr/local/lib/rustlib/x86_64-apple-darwin/lib/libcollections-4e7c5e5c.rlib" "/usr/local/lib/rustlib/x86_64-apple-darwin/lib/libunicode-4e7c5e5c.rlib" "/usr/local/lib/rustlib/x86_64-apple-darwin/lib/librand-4e7c5e5c.rlib" "/usr/local/lib/rustlib/x86_64-apple-darwin/lib/liballoc-4e7c5e5c.rlib" "/usr/local/lib/rustlib/x86_64-apple-darwin/lib/liblibc-4e7c5e5c.rlib" "/usr/local/lib/rustlib/x86_64-apple-darwin/lib/libcore-4e7c5e5c.rlib" "-L" "/Users/sam/dev/rexchange/target/debug" "-L" "/Users/sam/dev/rexchange/target/debug/deps" "-L" "/usr/local/lib/rustlib/x86_64-apple-darwin/lib" "-L" "/Users/sam/dev/rexchange/.rust/lib/x86_64-apple-darwin" "-L" "/Users/sam/dev/rexchange/lib/x86_64-apple-darwin" "-lc" "-lm" "-lSystem" "-lpthread" "-lc" "-lm" "-lcompiler-rt"
note: ld: warning: directory not found for option '-L/Users/sam/dev/rexchange/.rust/lib/x86_64-apple-darwin'
ld: warning: directory not found for option '-L/Users/sam/dev/rexchange/lib/x86_64-apple-darwin'
Undefined symbols for architecture x86_64:
  "orders::BidOrder::get_account_id::hbe8193f627eb0daf4ba", referenced from:
      main::h6e33cd0005718795haa in rexchange.o
  "orders::BidOrder::get_currency_price::hac0a15cbc8d29001Gba", referenced from:
      main::h6e33cd0005718795haa in rexchange.o
  "orders::BidOrder::get_commodity_amount::hce97000d2a1749beSba", referenced from:
      main::h6e33cd0005718795haa in rexchange.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

error: aborting due to previous error
Could not compile `rexchange`.

Caused by:
  Process didn't exit successfully: `rustc src/main.rs --crate-name rexchange --crate-type bin -g --out-dir /Users/sam/dev/rexchange/target/debug --emit=dep-info,link -L dependency=/Users/sam/dev/rexchange/target/debug -L dependency=/Users/sam/dev/rexchange/target/debug/deps --extern uuid=/Users/sam/dev/rexchange/target/debug/deps/libuuid-f80da2be6e37bdc9.rlib --extern rexchange=/Users/sam/dev/rexchange/target/debug/librexchange-4

I've no idea why this failure occurred and I couldn't find anything that looked similar. Can anyone explain to me what is going on and how to fix?

The code is: https://github.com/samphippen/rexchange

Answer 1

I can reproduce the issue, and have a workaround. I'm not sure if it's a Rust bug or not, but it's certainly surprising, so I'd encourage you to file it (or let me know and I can do it).

First, I created a new cargo project called repro. I then added these files:

lib.rs

mod order {
    pub struct Alpha(pub u8);

    impl Alpha {
        pub fn value(&self) -> u8 { self.0 }
    }
}

pub mod interface {
    use super::order::Alpha;

    pub fn yeah() -> Alpha { Alpha(8) }
}

main.rs

extern crate repro;

fn main() {
    println!("{:?}", repro::interface::yeah().value());
}

During compilation, this warning is generated:

src/lib.rs:5:9: 5:45 warning: method is never used: `value`, #[warn(dead_code)] on by default
src/lib.rs:5         pub fn value(&self) -> u8 { self.0 }
                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Which is surprising, as we indeed use it in main. Compilation then fails with the same linking error you saw.

The workaround is to mark the order module as public:

pub mod order {