"integral variable" error should suggest how to make literal a float

[sunjay]

The following code:

fn foo(x: f64) {}

fn main() {
    foo(10);
}

Produces the following error message:

error[E0308]: mismatched types
 --> src/main.rs:4:9
  |
4 |     foo(10);
  |         ^^ expected f64, found integral variable
  |
  = note: expected type `f64`
             found type `{integer}`

This error message tells you that the types are mismatched, but doesn't fully explain why. To fix it, you need to use a floating point literal instead of an integer literal. This isn't clear from the error message.

If you're new to programming or if you come from a language that doesn't draw the same distinction between integer and floating point literals, it may not be clear why the literal 10 is not the same as 10.0.

It would be great if we could add something in our error message that would suggest one or more of the valid ways to fix this:

• 10.0
• 10.
• 10f64 - type could be f32 in another context