Linker error with Float due to "plugin = true" in Cargo.toml

[paholg]

I get this error:

$ cargo run --example ex --verbose                                                                                                                   [4:51:51]
       Fresh libc v0.1.8
       Fresh rustc-serialize v0.3.14
       Fresh rand v0.3.8
   Compiling test v0.1.0 (file:///home/paho/projects/test)
     Running `rustc examples/ex.rs --crate-name ex --crate-type bin -g --out-dir /home/paho/projects/test/target/debug/examples --emit=dep-info,link -L dependency=/home/paho/projects/test/target/debug -L dependency=/home/paho/projects/test/target/debug/deps --extern num=/home/paho/projects/test/target/debug/deps/libnum-f51f78acffae6108.rlib --extern test=/home/paho/projects/test/target/debug/libtest.so`
       Fresh num v0.1.25
error: linking with `cc` failed: exit code: 1
note: "cc" "-Wl,--as-needed" "-m64" "-L" "/home/paho/.multirust/toolchains/nightly/lib/rustlib/x86_64-unknown-linux-gnu/lib" "/home/paho/projects/test/target/debug/examples/ex.o" "-o" "/home/paho/projects/test/target/debug/examples/ex" "-Wl,--whole-archive" "-l" "morestack" "-Wl,--no-whole-archive" "-Wl,--gc-sections" "-pie" "-nodefaultlibs" "-L" "/home/paho/projects/test/target/debug" "-l" "test" "-L" "/home/paho/.multirust/toolchains/nightly/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-l" "std-11582ce5" "-L" "/home/paho/projects/test/target/debug" "-L" "/home/paho/projects/test/target/debug/deps" "-L" "/home/paho/.multirust/toolchains/nightly/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-L" "/home/paho/projects/test/.rust/lib/x86_64-unknown-linux-gnu" "-L" "/home/paho/projects/test/lib/x86_64-unknown-linux-gnu" "-Wl,-Bstatic" "-Wl,-Bdynamic" "-l" "c" "-l" "m" "-l" "dl" "-l" "pthread" "-l" "rt" "-l" "gcc_s" "-l" "pthread" "-l" "c" "-l" "m" "-Wl,-rpath,$ORIGIN/.." "-Wl,-rpath,$ORIGIN/../../../../../.multirust/toolchains/nightly/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-rpath,/usr/local/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-l" "compiler-rt"
note: /home/paho/projects/test/target/debug/examples/ex.o: In function `ex::main':
/home/paho/projects/test/examples/ex.rs:7: undefined reference to `traits::f64.Float::sqrt::h209fd0d3f28f2049lci'
collect2: error: ld returned 1 exit status

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

Caused by:
  Process didn't exit successfully: `rustc examples/ex.rs --crate-name ex --crate-type bin -g --out-dir /home/paho/projects/test/target/debug/examples --emit=dep-info,link -L dependency=/home/paho/projects/test/target/debug -L dependency=/home/paho/projects/test/target/debug/deps --extern num=/home/paho/projects/test/target/debug/deps/libnum-f51f78acffae6108.rlib --extern test=/home/paho/projects/test/target/debug/libtest.so` (exit code: 101)
FAIL: 101

Given the following:

# Cargo.toml
[package]
  name = "test"
  version = "0.1.0"

[lib]
  name = "test"
  plugin = true

[dependencies]
  num = "*"

// src/lib.rs
extern crate num;

// examples/ex.rs
extern crate test;
extern crate num;

use num::traits::Float;

fn main() {
    1.0.sqrt();
}

Getting rid of any of plugin = true, extern crate num; in lib.rs, or extern crate test; causes the program to compile correctly.

This happens on both stable and nightly versions of rust.

[alexcrichton]

I believe that this is a dupe of #14344 as num is an rlib and it's not making its way into the dylib test.