Garbled compile errors when running cargo test

[Stebalien]

When compiling with cargo build, cargo forwards rustc's error messages without any issues. However, when compiling with cargo test, build errors are often garbled:

src/lib.rs:4:1: 6:2 error: duplicate definition of value `fialure`
src/lib.rs:4 fn fialure() {
src/lib.rs:5     bad;
src/lib.rs:6 }
src/lib.rs:1:1: 3:2 note: first definition of value `fialure` here
src/lib.rs:1 fn fialure() {
src/lib.rs:2     bad;
src/lib.rs:3 }
src/lib.rs:7:1: 9:2 error: duplicate definition of value `fialure`
src/lib.rs:7 fn fialure() {
src/lib.rs:8     bad;
src/lib.rs:9 }
src/lib.rs:4:1: 6:2 note: first definition of value `fialure` here
src/lib.rs:4 fn fialure() {
src/lib.rs:5     bad;
src/lib.rs:6 }
src/lib.rs:10:1: 12:2 error: duplicate definition of value `fialure`
src/lib.rs:10 fn fialure() {
src/lib.rs:11     bad;
src/lib.rs:12 }
src/lib.rs:7:1: 9:2 note: first definition of value `fialure` here
src/lib.rs:7 fn fialure() {
src/lib.rs:8     bad;
src/lib.rs:9 }
src/lib.rs:13:1: 15:2 error: duplicate definition of value `fialure`
src/lib.rs:13 fn fialure() {
src/lib.rs:14     bad;
src/lib.rs:15 }
src/lib.rs:10:1: 12:2 note: first definition of value `fialure` here
src/lib.rs:10 fn fialure() {
src/lib.rs:11     bad;
src/lib.rs:12 }
src/lib.rs:4:1: 6:2 src/lib.rs:16:1: 18:2 error: error: duplicate definition of value `fialure`duplicate definition of value `fialure`

src/lib.rssrc/lib.rs::416 fn fialure() { 
fn fialure() {src/lib.rs:
5 src/lib.rs    bad;
:src/lib.rs17:6  }    bad;

src/lib.rssrc/lib.rs:1:1: 3:2 :18note:  }
first definition of value `fialure` heresrc/lib.rs:13:1: 15:2
src/lib.rs :1 fn fialure() {note: 
src/lib.rs:2first definition of value `fialure` here     bad;
src/lib.rs:
3 }src/lib.rs:
13src/lib.rs:7:1: 9:2 fn fialure() { 
error: src/lib.rs:14duplicate definition of value `fialure`     bad;

src/lib.rssrc/lib.rs::715 fn fialure() { 
src/lib.rs}:8
     bad;
src/lib.rssrc/lib.rs:19:1: 21:2:9  }
src/lib.rs:4:1: 6:2error:  note: duplicate definition of value `fialure`first definition of value `fialure` here

src/lib.rssrc/lib.rs:4: fn fialure() {19
src/lib.rs: 5fn fialure() {
 src/lib.rs    bad;
:20src/lib.rs :6    bad; }

src/lib.rs:src/lib.rs:10:1: 12:221  }error: 
src/lib.rs:16:1: 18:2duplicate definition of value `fialure` 
src/lib.rs:note: 10 fn fialure() {
first definition of value `fialure` heresrc/lib.rs:11
     bad;
src/lib.rs:src/lib.rs:1612  }
fn fialure() {src/lib.rs:7:1: 9:2 
src/lib.rsnote: :17 first definition of value `fialure` here    bad;

src/lib.rssrc/lib.rs::718 fn fialure() { 
}src/lib.rs:
8     bad;
src/lib.rs:22:1: 24:2src/lib.rs: 9 }
error: src/lib.rs:13:1: 15:2 duplicate definition of value `fialure`error: 
duplicate definition of value `fialure`src/lib.rs
:src/lib.rs22:13  fn fialure() {fn fialure() {
src/lib.rs
:14src/lib.rs     bad;:
src/lib.rs23:15  }    bad;

src/lib.rs:10:1: 12:2 src/lib.rs:note: 24 }first definition of value `fialure` here

src/lib.rs:19:1: 21:2src/lib.rs: 10 fn fialure() {
note: src/lib.rs:11     bad;first definition of value `fialure` here
src/lib.rs:
12 }src/lib.rs
:19src/lib.rs:16:1: 18:2  fn fialure() {error: 
src/lib.rs:duplicate definition of value `fialure`20 
src/lib.rs    bad;:
16 src/lib.rsfn fialure() {
:src/lib.rs:2117      bad;
}src/lib.rs:
18 }
src/lib.rs:25:1: 27:2src/lib.rs:13:1: 15:2  note: error: first definition of value `fialure` here
src/lib.rsduplicate definition of value `fialure`:13 
fn fialure() {
src/lib.rssrc/lib.rs::1425     bad; 
src/lib.rsfn fialure() {:15
 }src/lib.rs
:src/lib.rs:19:1: 21:226  error:     bad;
src/lib.rsduplicate definition of value `fialure`:27
src/lib.rs }:19
 fn fialure() {
src/lib.rssrc/lib.rs:22:1: 24:2: 20     bad;
note: src/lib.rs:21 }
first definition of value `fialure` heresrc/lib.rs:16:1: 18:2 
note: src/lib.rs:first definition of value `fialure` here22 
src/lib.rsfn fialure() {:
16 src/lib.rsfn fialure() {
:src/lib.rs:2317      bad;
    bad;src/lib.rs:
18 src/lib.rs}
:24src/lib.rs:22:1: 24:2  }error: 
duplicate definition of value `fialure`
error: src/lib.rs:22 aborting due to 8 previous errorsfn fialure() {
src/lib.rs:
23     bad;
src/lib.rs:24 }
src/lib.rs:19:1: 21:2 note: first definition of value `fialure` here
src/lib.rs:19 fn fialure() {
src/lib.rs:20     bad;
src/lib.rs:21 }
src/lib.rs:25:1: 27:2 error: duplicate definition of value `fialure`
src/lib.rs:25 fn fialure() {
src/lib.rs:26     bad;
src/lib.rs:27 }
src/lib.rs:22:1: 24:2 note: first definition of value `fialure` here
src/lib.rs:22 fn fialure() {
src/lib.rs:23     bad;
src/lib.rs:24 }
error: aborting due to 8 previous errors
Build failed, waiting for other jobs to finish...
Could not compile `tmp`.

To learn more, run the command again with --verbose.

Test code (intentionally broken):

fn fialure() {
    bad;
}
fn fialure() {
    bad;
}
fn fialure() {
    bad;
}
fn fialure() {
    bad;
}
fn fialure() {
    bad;
}
fn fialure() {
    bad;
}
fn fialure() {
    bad;
}
fn fialure() {
    bad;
}
fn fialure() {
    bad;
}
#[test]
fn it_works() {
    failure()
}

rustc --test does not exhibit the same behavior.

[alexcrichton]

Thanks for the report! What's actually happening here is that the library is being compiled twice (once with --test and once for doc tests later on), and this is a dupe of #1534 and #851. This is intended behavior though, and you can use various flags like --test, --lib, or -j to not run rustc in parallel, so I'm going to close this.