Suggest using ranges in loops on primitive types, instead of calling .iter()

[alexandermerritt]

The following code results in output that isn't specifically helpful:

fn main() {
    let max: usize = 10;
    for m in max { ; }
}

Compiler output:

error: the trait bound `usize: std::iter::Iterator` is not satisfied [--explain E0277]
 --> <anon>:3:5
3 |>     for m in max {
  |>     ^
note: `usize` is not an iterator; maybe try calling `.iter()` or a similar method
note: required by `std::iter::IntoIterator::into_iter`

Primitive types do not [currently] implement Iterator. Perhaps the output could see the type is primitive and suggest to create a type that implements Iterator, such as a range with 0..max?

Meta

rustc 1.11.0-nightly (bb4a79b08 2016-06-15)
binary: rustc
commit-hash: bb4a79b087158f396b984bdf552d2c90890b12a3
commit-date: 2016-06-15
host: x86_64-unknown-linux-gnu
release: 1.11.0-nightly

[Aatch]

That error message is already somewhat special, but it uses a special attribute on the trait itself. This would require actually special-casing Iterator in this case, and I'm not sure how useful that would be for the effort. I'm skeptical that this kind of thing is 1) particularly common and 2) something that somebody would deliberately do. What I mean by that second point is that there's a difference between doing for m in max and going "oh I meant for m in 0..max and doing that expecting it to work.

[alexandermerritt]

@Aatch These are valid points. I agree that if not trivial to implement, it doesn't make sense given this is probably a rare occurrence.

Mainly I was thinking the easiest could be expanding the already existing hint (hard-coded string?) to perhaps be maybe try calling .iter() or create a Range if this is a primitive type with 0..max which avoids adding any special-case handling internally.

[estebank]

Once #47613 gets merged, this can be trivially added.