Possible misbehavior in rustc cfg_attr(test, allow(dead_code))

compiler output

   Compiling warn v0.1.0 (file:///home/cbiffle/proj/rs/warn)
src/lib.rs:2:3: 2:31 warning: function is never used: `tested`, #[warn(dead_code)] on by default
src/lib.rs:2   pub fn tested() -> i32 { 0 }
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/lib.rs:5:3: 5:33 warning: function is never used: `untested`, #[warn(dead_code)] on by default
src/lib.rs:5   pub fn untested() -> i32 { 0 }
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     Running target/debug/warn-fef74f9367799b2e

running 1 test
test sub::tests::test ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured

   Doc-tests warn

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured

lib.rs

mod sub {
  pub fn tested() -> i32 { 0 }

  #[cfg_attr(test, allow(dead_code))]
  pub fn untested() -> i32 { 0 }

  #[cfg(test)]
  mod tests {
    use super::*;

    #[test]
    fn test() {
      assert_eq!(0, tested())
    }
  }
}