unhelpful error message when declaring constant with type parameter's associated constant

[tspiteri]

For this code:

trait Foo {
    const BAR: i32;
}
impl Foo for i32 {
    const BAR: i32 = 42;
}
fn baz<F: Foo>(a: F) {
    const QUX: i32 = F::BAR;
    println!("{}", QUX);
}
fn main() {
    baz(1i32);
}

I get the error message:

| fn baz<F: Foo>(a: F) {
|    --- - type variable from outer function
|    |
|    try adding a local type parameter in this method instead
|     const QUX: i32 = F::BAR;
|                      ^^^^^^ use of type variable from outer function

QUX is not a method and cannot have local type parameters; I don't think constants can be generic. So the error message is confusing.

[oli-obk]

Additionally, the try adding a local type parameter in this method instead is pointing to the outer function instead of the item that is supposed to become generic

[estebank]

Current output:

error[E0401]: can't use generic parameters from outer function
 --> src/main.rs:8:22
  |
7 | fn baz<F: Foo>(a: F) {
  |        - type parameter from outer function
8 |     const QUX: i32 = F::BAR;
  |                      ^^^^^^ use of generic parameter from outer function

[sgued]

I still found the current error message confusing. In my case it wasn't with a variable but within the type parameter:

fn testing<T>() {
    const TESTING: [T; 0] = [];
}

gives the following error:

error[[E0401]](https://doc.rust-lang.org/nightly/error-index.html#E0401): can't use generic parameters from outer function
 --> src/main.rs:3:21
  |
2 | fn testing<T>() {
  |            - type parameter from outer function
3 |     const TESTING: [T; 0] = [];
  |                     ^ use of generic parameter from outer function

For more information about this error, try `rustc --explain E0401`.

rustc --explain E0401 doesn't mention consts or statics, it seems to me that it should.

[Dylan-DPC]

Current output:

error[E0401]: can't use generic parameters from outer item
 --> src/main.rs:8:22
  |
7 | fn baz<F: Foo>(a: F) {
  |        - type parameter from outer item
8 |     const QUX: i32 = F::BAR;
  |                      ^^^^^^ use of generic parameter from outer item
  |
  = note: a `const` is a separate item from the item that contains it

warning: unused variable: `a`
 --> src/main.rs:7:16
  |
7 | fn baz<F: Foo>(a: F) {
  |                ^ help: if this is intentional, prefix it with an underscore: `_a`
  |
  = note: `#[warn(unused_variables)]` on by default