More informative error messages when using #[test] or #fmt without std

[marijnh]

Currently, you'll get an unexplained

error: unresolved modulename: std

Which is bound to confuse people.

[marijnh]

Maybe we should automagically link in std when compiling with --test.

[brson]

I was hoping for the syntax extension plugin system to materialize and offer a way to declare runtime dependencies, but maybe we should just hack something up for 0.1. It's a common error.

[graydon]

Both are in core now. I think this is obsolete.

[brson]

The test runner is still in std, so I think this is still a problem.

[catamorphism]

Is this fixed? #1448 suggests it is, but @brson 's comment from a month ago post-dates #1448 being closed.

[brson]

Not fixed. This still happens when compiling tests for crates that don't use std.

[killerswan]

Yeah, this confused me.

[nejucomo]

There are three issues here, which this log shows:

$ cat ./test_compile_error_example.rs
fn inc_int(x: int) -> int { x + 1 }


#[test]
fn test_inc_int() {
  assert (inc_int(3) == 4);
}

$ rustc --test ./test_compile_error_example.rs
./test_compile_error_example.rs:1:0: 1:0 error: unresolved name
./test_compile_error_example.rs:1 fn inc_int(x: int) -> int { x + 1 }
                                  ^
./test_compile_error_example.rs:1:0: 1:0 error: use of undeclared module `std::test`
./test_compile_error_example.rs:1 fn inc_int(x: int) -> int { x + 1 }
                                  ^
./test_compile_error_example.rs:1:0: 1:0 error: unresolved name: std::test::test_main
./test_compile_error_example.rs:1 fn inc_int(x: int) -> int { x + 1 }
                                  ^
./test_compile_error_example.rs:1:0: 1:0 error: unresolved name
./test_compile_error_example.rs:1 fn inc_int(x: int) -> int { x + 1 }
                                  ^
./test_compile_error_example.rs:1:0: 1:0 error: use of undeclared module `std::test`
./test_compile_error_example.rs:1 fn inc_int(x: int) -> int { x + 1 }
                                  ^
./test_compile_error_example.rs:1:0: 1:0 error: use of undeclared type name `std::test::test_desc`
./test_compile_error_example.rs:1 fn inc_int(x: int) -> int { x + 1 }
                                  ^
error: aborting due to 6 previous errors

1. The tutorial doesn't mention the need for "use std" when passing --test, so there is a doc bug.
2. The location of the errors is confusing. Shouldn't the location be where the #[test] annotation is found? In this example, that's line 3, not line 1. (Related to Issue Macro errors are reported at def, not use #1448 ?)
3. There are two errors which seem unrelated to "std::test", the first and the fourth. Which name is unresolved?

Should we file separate tickets for these three cases? Is 2 here a duplicate of #1448 or is it a distinct bug?

Is there any way to make the errors in 3 more clear? If so, is it a general problem and fix that should be a separate github issue?

[nejucomo]

I added a distinct ticket about making the tutorial more explicit: #3241

[nejucomo]

I added a separate ticket about the first and fourth error messages which are "unresolved name", because it's not clear which name is unresolved: #3242

[brson]

Compiling with --test now automatically links to std.