Properly suggest fn when function is used

[ghost]

Given the following code:

function foo() {}

The current output is:

error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `foo`
 --> src/main.rs:2:11
  |
2 |  function foo() {}
  |           ^^^ expected one of 8 possible tokens

Ideally the output should look like: help: you likely meant to define a function using the `fn` keyword instead

---

Rustc already does this to an extent, for eg. here

pub function foo() {}

error: visibility `pub` is not followed by an item
 --> src/main.rs:2:1
  |
2 | pub function foo() {}
  | ^^^ the visibility
  |
  = help: you likely meant to define an item, e.g., `pub fn foo() {}`

However, using a similar implementation to #99903, this could become ideal.

@rustbot claim

[Rageking8]

Possible duplicate of #99751

[ghost]

Ah, that is a duplicate. Thanks for reporting!