New #[test] export logic creates wonky error messages

[djrenren]

#[test] fn foo(){}
#[test] fn foo(){}

produces:

error[E0252]: the name `foo` is defined multiple times
  --> ./test.rs:20:8
   |
13 | pub fn foo() {
   |        --- previous import of the value `foo` here
...
20 | pub fn foo() {
   |        ^^^ `foo` reimported here
   |
   = note: `foo` must be defined only once in the value namespace of this module
help: You can use `as` to change the binding name of the import
   |
20 | pub fn foo as other_foo() {
   |        ^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0252`.

PR responsible (sorry!): #52890

[djrenren]

Wait this may just be a local issue from my build. I'll reopen if I encounter it on a fresh build.

[djrenren]

Confirmed on nightly in rust playground.

This should be a simple ExpansionData issue, but i have no idea how that works? @eddyb? @petrochenkov?

[eddyb]

What you're generating is effectively this, right?

pub fn foo_1() {}
pub fn foo_2() {}
use foo_1 as foo;
use foo_2 as foo;

For the record, without your transformations, this happens:

pub fn foo() {}
pub fn foo() {}

error[E0428]: the name `foo` is defined multiple times
 --> src/lib.rs:2:1
  |
1 | pub fn foo() {}
  | ------------ previous definition of the value `foo` here
2 | pub fn foo() {}
  | ^^^^^^^^^^^^ `foo` redefined here
  |
  = note: `foo` must be defined only once in the value namespace of this module`

One thing you could do, in order to reproduce that error, is make sure you reuse the same gensym for the same original name, instead of making separate ones always.
You can probably just have a global map of them, and not worry where they came from.

Then you'd be generating this:

pub fn foo_() {}
pub fn foo_() {}
use foo_ as foo;
use foo_ as foo;

error[E0428]: the name `foo_` is defined multiple times
 --> src/lib.rs:2:1
  |
1 | pub fn foo_() {}
  | ------------- previous definition of the value `foo_` here
2 | pub fn foo_() {}
  | ^^^^^^^^^^^^^ `foo_` redefined here
  |
  = note: `foo_` must be defined only once in the value namespace of this module

error[E0252]: the name `foo` is defined multiple times
 --> src/lib.rs:4:5
  |
3 | use foo_ as foo;
  |     ----------- previous import of the value `foo` here
4 | use foo_ as foo;
  |     ^^^^^^^^^^^ `foo` reimported here
  |
  = note: `foo` must be defined only once in the value namespace of this module
help: You can use `as` to change the binding name of the import
  |
4 | use foo_ as foo as other_foo;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^

At least this way, the user can see the original error message, even if it's doubled-up.

[matthewjasper]

Closing as this is no longer an issue. Output on nightly

error[E0428]: the name `foo` is defined multiple times
 --> <source>:6:9
  |
5 | #[test] fn foo(){}
  |         -------- previous definition of the value `foo` here
6 | #[test] fn foo(){}
  |         ^^^^^^^^ `foo` redefined here
  |
  = note: `foo` must be defined only once in the value namespace of this module
error: aborting due to previous error
For more information about this error, try `rustc --explain E0428`.
Compiler returned: 1