`cargo test` compiles twice

[nixpulvis]

Running cargo test compiles the code twice before running the compiled tester binary. This is obviously irritating to look at when there are a bunch of warnings and the like, and is also much slower.

[alexcrichton]

Can you provide an example to look at? What's probably happening is that cargo is running rustc src/lib.rs and rustc --test src/lib.rs, and then after the lib finishes building it rust rustc tests/foo.rs -L target.

If you don't want to build your library with --test then you can specify test = false in the manifest.

[nixpulvis]

Here is a run of cargo test on a project I'm working on. As you can see it's printing the errors twice. I would expect cargo test to only run rustc --test src/lib.rs && target/parser-<something>.

> cargo test
   Compiling parser v0.0.1 (file:///Users/nixpulvis/Code/parser)
/Users/nixpulvis/Code/parser/src/lexer.rs:15:7: 21:4 error: cannot infer an appropriate lifetime due to conflicting requirements
/Users/nixpulvis/Code/parser/src/lexer.rs:15:7: 21:4 error: cannot infer an appropriate lifetime due to conflicting requirements
/Users/nixpulvis/Code/parser/src/lexer.rs:15   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:16     if s.len() >= l && s[0..l] == value {
/Users/nixpulvis/Code/parser/src/lexer.rs:15   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:17       Success(box LiteralNode(s[0..l]), s[l..])
/Users/nixpulvis/Code/parser/src/lexer.rs:16     if s.len() >= l && s[0..l] == value {
/Users/nixpulvis/Code/parser/src/lexer.rs:18     } else {
/Users/nixpulvis/Code/parser/src/lexer.rs:17       Success(box LiteralNode(s[0..l]), s[l..])
/Users/nixpulvis/Code/parser/src/lexer.rs:19       Error
/Users/nixpulvis/Code/parser/src/lexer.rs:18     } else {
/Users/nixpulvis/Code/parser/src/lexer.rs:20     }
                                             ...
/Users/nixpulvis/Code/parser/src/lexer.rs:19       Error
/Users/nixpulvis/Code/parser/src/lexer.rs:20     }
                                             ...
/Users/nixpulvis/Code/parser/src/lexer.rs:12:45: 22:2 note: first, the lifetime cannot outlive the block at 12:44...
/Users/nixpulvis/Code/parser/src/lexer.rs:12 pub fn lit<'a>(value: &'a str) -> Lexer<'a> {
/Users/nixpulvis/Code/parser/src/lexer.rs:13   let l = value.len();
/Users/nixpulvis/Code/parser/src/lexer.rs:14 
/Users/nixpulvis/Code/parser/src/lexer.rs:15   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:16     if s.len() >= l && s[0..l] == value {
/Users/nixpulvis/Code/parser/src/lexer.rs:17       Success(box LiteralNode(s[0..l]), s[l..])
                                             ...
/Users/nixpulvis/Code/parser/src/lexer.rs:12:45: 22:2 note: first, the lifetime cannot outlive the block at 12:44...
/Users/nixpulvis/Code/parser/src/lexer.rs:12 pub fn lit<'a>(value: &'a str) -> Lexer<'a> {
/Users/nixpulvis/Code/parser/src/lexer.rs:13   let l = value.len();
/Users/nixpulvis/Code/parser/src/lexer.rs:14 
/Users/nixpulvis/Code/parser/src/lexer.rs:15   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:16     if s.len() >= l && s[0..l] == value {
/Users/nixpulvis/Code/parser/src/lexer.rs:17       Success(box LiteralNode(s[0..l]), s[l..])
                                             ...
/Users/nixpulvis/Code/parser/src/lexer.rs:16:35: 16:40 note: ...so that captured variable `value` does not outlive the enclosing closure
/Users/nixpulvis/Code/parser/src/lexer.rs:16     if s.len() >= l && s[0..l] == value {
                                                                               ^~~~~
/Users/nixpulvis/Code/parser/src/lexer.rs:16:35: 16:40 note: ...so that captured variable `value` does not outlive the enclosing closure
/Users/nixpulvis/Code/parser/src/lexer.rs:16     if s.len() >= l && s[0..l] == value {
                                                                               ^~~~~
/Users/nixpulvis/Code/parser/src/lexer.rs:12:45: 22:2 note: but, the lifetime must be valid for the lifetime 'a as defined on the block at 12:44...
/Users/nixpulvis/Code/parser/src/lexer.rs:12 pub fn lit<'a>(value: &'a str) -> Lexer<'a> {
/Users/nixpulvis/Code/parser/src/lexer.rs:13   let l = value.len();
/Users/nixpulvis/Code/parser/src/lexer.rs:14 
/Users/nixpulvis/Code/parser/src/lexer.rs:15   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:16     if s.len() >= l && s[0..l] == value {
/Users/nixpulvis/Code/parser/src/lexer.rs:17       Success(box LiteralNode(s[0..l]), s[l..])
/Users/nixpulvis/Code/parser/src/lexer.rs:12:45: 22:2 note: but, the lifetime must be valid for the lifetime 'a as defined on the block at 12:44...
                                             ...
/Users/nixpulvis/Code/parser/src/lexer.rs:12 pub fn lit<'a>(value: &'a str) -> Lexer<'a> {
/Users/nixpulvis/Code/parser/src/lexer.rs:13   let l = value.len();
/Users/nixpulvis/Code/parser/src/lexer.rs:14 
/Users/nixpulvis/Code/parser/src/lexer.rs:15   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:16     if s.len() >= l && s[0..l] == value {
/Users/nixpulvis/Code/parser/src/lexer.rs:17       Success(box LiteralNode(s[0..l]), s[l..])
/Users/nixpulvis/Code/parser/src/lexer.rs:15:3: 21:4 note: ...so that it can be closed over into an object
/Users/nixpulvis/Code/parser/src/lexer.rs:15   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:16     if s.len() >= l && s[0..l] == value {
/Users/nixpulvis/Code/parser/src/lexer.rs:17       Success(box LiteralNode(s[0..l]), s[l..])
/Users/nixpulvis/Code/parser/src/lexer.rs:18     } else {
/Users/nixpulvis/Code/parser/src/lexer.rs:19       Error
/Users/nixpulvis/Code/parser/src/lexer.rs:20     }
                                             ...
                                             ...
/Users/nixpulvis/Code/parser/src/lexer.rs:15:3: 21:4 note: ...so that it can be closed over into an object
/Users/nixpulvis/Code/parser/src/lexer.rs:15   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:16     if s.len() >= l && s[0..l] == value {
/Users/nixpulvis/Code/parser/src/lexer.rs:17       Success(box LiteralNode(s[0..l]), s[l..])
/Users/nixpulvis/Code/parser/src/lexer.rs:18     } else {
/Users/nixpulvis/Code/parser/src/lexer.rs:19       Error
/Users/nixpulvis/Code/parser/src/lexer.rs:20     }
                                             ...
/Users/nixpulvis/Code/parser/src/lexer.rs:25:7: 31:4 error: cannot infer an appropriate lifetime due to conflicting requirements
/Users/nixpulvis/Code/parser/src/lexer.rs:25:7: 31:4 error: cannot infer an appropriate lifetime due to conflicting requirements
/Users/nixpulvis/Code/parser/src/lexer.rs:25   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:26     let r1 = (*l1).call((s,));
/Users/nixpulvis/Code/parser/src/lexer.rs:25   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:27     match r1 {
/Users/nixpulvis/Code/parser/src/lexer.rs:26     let r1 = (*l1).call((s,));
/Users/nixpulvis/Code/parser/src/lexer.rs:28       Success(_, _) => return r1,
/Users/nixpulvis/Code/parser/src/lexer.rs:27     match r1 {
/Users/nixpulvis/Code/parser/src/lexer.rs:29       Error => return (*l2).call((s,)),
/Users/nixpulvis/Code/parser/src/lexer.rs:28       Success(_, _) => return r1,
/Users/nixpulvis/Code/parser/src/lexer.rs:30     }
/Users/nixpulvis/Code/parser/src/lexer.rs:29       Error => return (*l2).call((s,)),
/Users/nixpulvis/Code/parser/src/lexer.rs:30     }
                                             ...
                                             ...
/Users/nixpulvis/Code/parser/src/lexer.rs:24:59: 32:2 note: first, the lifetime cannot outlive the block at 24:58...
/Users/nixpulvis/Code/parser/src/lexer.rs:24:59: 32:2 note: first, the lifetime cannot outlive the block at 24:58...
/Users/nixpulvis/Code/parser/src/lexer.rs:24 pub fn alt<'a>(l1: Lexer<'a>, l2: Lexer<'a>) -> Lexer<'a> {
/Users/nixpulvis/Code/parser/src/lexer.rs:24 pub fn alt<'a>(l1: Lexer<'a>, l2: Lexer<'a>) -> Lexer<'a> {
/Users/nixpulvis/Code/parser/src/lexer.rs:25   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:25   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:26     let r1 = (*l1).call((s,));
/Users/nixpulvis/Code/parser/src/lexer.rs:26     let r1 = (*l1).call((s,));
/Users/nixpulvis/Code/parser/src/lexer.rs:27     match r1 {
/Users/nixpulvis/Code/parser/src/lexer.rs:27     match r1 {
/Users/nixpulvis/Code/parser/src/lexer.rs:28       Success(_, _) => return r1,
/Users/nixpulvis/Code/parser/src/lexer.rs:28       Success(_, _) => return r1,
/Users/nixpulvis/Code/parser/src/lexer.rs:29       Error => return (*l2).call((s,)),
/Users/nixpulvis/Code/parser/src/lexer.rs:29       Error => return (*l2).call((s,)),
                                             ...
                                             ...
/Users/nixpulvis/Code/parser/src/lexer.rs:29:25: 29:27 note: ...so that captured variable `l2` does not outlive the enclosing closure
/Users/nixpulvis/Code/parser/src/lexer.rs:29:25: 29:27 note: ...so that captured variable `l2` does not outlive the enclosing closure
/Users/nixpulvis/Code/parser/src/lexer.rs:29       Error => return (*l2).call((s,)),
/Users/nixpulvis/Code/parser/src/lexer.rs:29       Error => return (*l2).call((s,)),
                                                                     ^~
                                                                     ^~
/Users/nixpulvis/Code/parser/src/lexer.rs:24:59: 32:2 note: but, the lifetime must be valid for the lifetime 'a as defined on the block at 24:58...
/Users/nixpulvis/Code/parser/src/lexer.rs:24:59: 32:2 note: but, the lifetime must be valid for the lifetime 'a as defined on the block at 24:58...
/Users/nixpulvis/Code/parser/src/lexer.rs:24 pub fn alt<'a>(l1: Lexer<'a>, l2: Lexer<'a>) -> Lexer<'a> {
/Users/nixpulvis/Code/parser/src/lexer.rs:24 pub fn alt<'a>(l1: Lexer<'a>, l2: Lexer<'a>) -> Lexer<'a> {
/Users/nixpulvis/Code/parser/src/lexer.rs:25   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:25   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:26     let r1 = (*l1).call((s,));
/Users/nixpulvis/Code/parser/src/lexer.rs:26     let r1 = (*l1).call((s,));
/Users/nixpulvis/Code/parser/src/lexer.rs:27     match r1 {
/Users/nixpulvis/Code/parser/src/lexer.rs:27     match r1 {
/Users/nixpulvis/Code/parser/src/lexer.rs:28       Success(_, _) => return r1,
/Users/nixpulvis/Code/parser/src/lexer.rs:28       Success(_, _) => return r1,
/Users/nixpulvis/Code/parser/src/lexer.rs:29       Error => return (*l2).call((s,)),
/Users/nixpulvis/Code/parser/src/lexer.rs:29       Error => return (*l2).call((s,)),
                                             ...
                                             ...
/Users/nixpulvis/Code/parser/src/lexer.rs:25:3: 31:4 note: ...so that it can be closed over into an object
/Users/nixpulvis/Code/parser/src/lexer.rs:25:3: 31:4 note: ...so that it can be closed over into an object
/Users/nixpulvis/Code/parser/src/lexer.rs:25   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:25   box |&: s: &'a str| {
/Users/nixpulvis/Code/parser/src/lexer.rs:26     let r1 = (*l1).call((s,));
/Users/nixpulvis/Code/parser/src/lexer.rs:26     let r1 = (*l1).call((s,));
/Users/nixpulvis/Code/parser/src/lexer.rs:27     match r1 {
/Users/nixpulvis/Code/parser/src/lexer.rs:27     match r1 {
/Users/nixpulvis/Code/parser/src/lexer.rs:28       Success(_, _) => return r1,
/Users/nixpulvis/Code/parser/src/lexer.rs:28       Success(_, _) => return r1,
/Users/nixpulvis/Code/parser/src/lexer.rs:29       Error => return (*l2).call((s,)),
/Users/nixpulvis/Code/parser/src/lexer.rs:29       Error => return (*l2).call((s,)),
/Users/nixpulvis/Code/parser/src/lexer.rs:30     }
/Users/nixpulvis/Code/parser/src/lexer.rs:30     }
                                             ...
                                             ...
error: aborting due to 2 previous errors
error: aborting due to 2 previous errors
Build failed, waiting for other jobs to finish...
Could not compile `parser`.

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

[alexcrichton]

Do you have any binaries or integration tests ([test]) specified in the manifest or discovered implicitly? If I could take a peek at the code that would also be useful.

[nixpulvis]

Here is the code. It's a tiny project at the moment because I can't figure out boxed unboxed closures 😜 but testing it with cargo test will yield duplicate warnings on master.

There are #[test]s.

[alexcrichton]

Hm, did you mean to include a link in there?

[nixpulvis]

Oh man, it's going to be a long night, already losing my mind. Here you go. https://github.com/nixpulvis/parser

[alexcrichton]

Aha! That definitely shouldn't be compiling twice, thanks @nixpulvis! I'll take a look into this hopefully soon.

[nixpulvis]

❤️

[SimonSapin]

Isn’t the other compile a dependency of running rustdoc --test? You can disable this with doctest = false in Cargo.toml, but it would be nice if Cargo did that implicitly when it can figure out that the source does not contain any doctest. (Though I’m not sure how it would do that, maybe split rustdoc --test into doctest collection (which doesn’t require the crate to be built) and doctest compile/run?)

[nixpulvis]

I don't think doctests should be opt in. I like that they are part of cargo test. It's just hard to read the warnings are errors as is.

This might be a bad idea, but maybe it actually might make sense to allow rustc to include doctests when passes an additional flag.

[SimonSapin]

I don’t mean making doctest opt-in, only to avoid running zero doctests when Cargo can determine there are indeed zero, if that can be determine quickly.

[nixpulvis]

But then the moment you add doctests then your back into the same problem.

[SimonSapin]

I don’t see the problem. When you add doctests you don’t have zero doctests anymore and so Cargo should not detect that you have zero doctests anymore (again, assuming this detection is feasible) and would start running doctests again. This magic "detection" would run every time you run cargo test.

[nixpulvis]

The problem is with the original problem of showing two compilations right next to each other with all their warnings and errors.

[SimonSapin]

Ah, sorry I misunderstood. Yes indeed. I believe the reason for that is that rustdoc --test need a library to link against, but rustc --test creates an executable with the test harness, not a library.