Suggest to create a new const item if the fn in the array is a const fn

[henryboisdequin]

Fixes #73734. If the fn in the array repeat expression is a const fn, suggest creating a new const item. On nightly, suggest creating an inline const block. This PR also removes the suggest_const_in_array_repeat_expressions as it is no longer necessary.

Example:

fn main() {
    // Should not compile but hint to create a new const item (stable) or an inline const block (nightly)
    let strings: [String; 5] = [String::new(); 5];
    println!("{:?}", strings);
}

Gives this error:

error[E0277]: the trait bound `std::string::String: std::marker::Copy` is not satisfied
 --> $DIR/const-fn-in-vec.rs:3:32
  |
2 |     let strings: [String; 5] = [String::new(); 5];
  |                             ^^^^^^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `String`
  |
  = note: the `Copy` trait is required because the repeated element will be copied

With this change, this is the error message:

error[E0277]: the trait bound `String: Copy` is not satisfied
  --> $DIR/const-fn-in-vec.rs:3:32
   |
LL |     let strings: [String; 5] = [String::new(); 5];
   |                                ^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `String`
   |
   = help: moving the function call to a new `const` item will resolve the error

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @matthewjasper (or someone else) soon.

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[henryboisdequin]

I'm looking into the errors.

[henryboisdequin]

r? @Aaron1011

[henryboisdequin]

@rustbot label -S-waiting-on-author +S-waiting-on-review

[Aaron1011]

I helped with writing this PR, so let's get someone else to do a final review.

r? @estebank

[tesuji]

Does this PR conflict with #80404, which removes const_in_array_repeat_expressions feature ?

[Aaron1011]

They touch the same files, but this PR removes the specialized diagnostic for that feature, so everything should be fine after a rebase.

[henryboisdequin]

@estebank Do I need to make any further changes?

[henryboisdequin]

Friendly ping @estebank :)

[henryboisdequin]

@estebank Done ✅

[estebank]

@bors r+

[bors]

📌 Commit 64fe2c1 has been approved by estebank