Same run, Different ouputs

[frntn]

What I do

Trying to cargo test against some code

What I got

Don't freak out the underlying error is coherent and is exactly the same :)
BUT
The ouput may appear broken like if two threads are writing to stdout at the same time, so the output variants appear to be infinite like these :

# RUN KO 1
→ cargo test
   Compiling lists v0.1.0 (file:///lab/rust/lists)
src/second.rs:56:6: 56:7 src/second.rs:56:6: 56:7 error: expected ident, found `&`error: 
expected ident, found `&`
src/second.rs:56 src/second.rs:impl<&T> Iterator for List<&T> {
56 impl<&T> Iterator for List<&T> {                      
                      ^
^
Build failed, waiting for other jobs to finish...
Could not compile `lists`.

# RUN KO 2
→ cargo test
   Compiling lists v0.1.0 (file:///lab/rust/lists)
src/second.rs:56:6: 56:7src/second.rs:56:6: 56:7  error: error: expected ident, found `&`
expected ident, found `&`src/second.rs:56
 impl<&T> Iterator for List<&T> {
src/second.rs                      :56^ impl<&T> Iterator for List<&T> {

                      ^
Build failed, waiting for other jobs to finish...
Could not compile `lists`.

# RUN KO 3
→ cargo test
   Compiling lists v0.1.0 (file:///lab/rust/lists)
src/second.rs:56:6: 56:7src/second.rs:56:6: 56:7  error: error: expected ident, found `&`
src/second.rs:56expected ident, found `&` impl<&T> Iterator for List<&T> {

^
src/second.rs:56 impl<&T> Iterator for List<&T> {

# etc...

Note: No code change or anything between the runs. Just re-exec build test

This messes up understanding, indicators and maybe colors...

What I expected

What I end up with on some runs :

# RUN OK 
   Compiling lists v0.1.0 (file:///lab/rust/lists)
src/second.rs:56:6: 56:7 error: expected ident, found `&`
src/second.rs:56 impl<&T> Iterator for List<&T> {
                      ^
src/second.rs:56:6: 56:7 error: expected ident, found `&`
src/second.rs:56 impl<&T> Iterator for List<&T> {
                      ^
Build failed, waiting for other jobs to finish...
Could not compile `lists`.

How to reproduce

The code used for the code samples of this issue (generating these errors) is available here : https://gist.github.com/frntn/e9e5652c12fdc931315d

---

Ubuntu 14.04.2 LTS
rustc 1.1.0 (35ceea399 2015-06-19)
cargo 0.2.0-nightly (a483581 2015-05-14) (built 2015-05-15)

[alexcrichton]

This is actually intentional because Cargo is running the compiler in parallel behind the scenes. For more info see this comment: #1717 (comment)

[frntn]

This is actually intentional

hmmm...
What's intentional here is running the compiler in parallel, not having a mixed ouput.
Am I right ? (I'm confident you'll answer yes to this one, so I proceed)

If so, this is actually an issue!

I know everybody is working hard on developing Cargo and making it a top level tool, but this kind of output behavior + your answer can scare people out and make them loose confidence about the way Cargo and Rust are developped.
Don't misunderstand me here : I believe they would be wrong!

Resolution patterns :
I am thinking of other tools using parallel runs and concurrent ouput like Packer for example. They have choosen to control their mixed ouput by lines, with each line prefixed by some identifier with a distinct color.

I haven't done any research about that, but I'm pretty sure we can find other implementations to solve this concurrent ouput issue.

[alexcrichton]

Ok, seems reasonable to consider the symptom solvable without not parallelizing.

[MrSapps]

MsBuild solves this problem by numbering the "node/thread/compiler" instances. So you'll see something like

1> foo.cpp
2> bar.cpp

[alexcrichton]

Ah I think this is a dupe of #1198 which is also about interleaving output