add hint for =< as <=

[zacklukem]

Adds a compiler hint for when =< is typed instead of <=

Example hint:

fn foo() {
    if 1 =< 3 {
        println!("Hello, World!");
    }
}

error: expected type, found `3`
 --> main.rs:2:13
  |
2 |     if 1 =< 3 {
  |          -- ^ expected type
  |          |
  |          help: did you mean: `<=`

This PR only emits the suggestion if there is no space between the = and <. This hopefully narrows the scope of when this error is emitted, however this still allows this error to be emitted in cases such as this:

error: expected expression, found `;`
 --> main.rs:2:18
  |
2 |     if 1 =< [i32;; 3]>::hello() {
  |          --      ^ expected expression
  |          |
  |          help: did you mean: `<=`

Which could be a good reason not to merge since I haven't been able to think of any other ways of narrowing the scope of this diagnostic.

closes #111128

[rustbot]

r? @oli-obk

(rustbot has picked a reviewer for you, use r? to override)

[oli-obk]

I am wondering if the current logic could end up with weird spans in case of x =thing!() where thing!() expands to something starting with <. I can't come up with anything as a test, but maybe we should still guard against it by requiring that the spans' expansion info is the same?

[compiler-errors]

This happens before macro expansion though. I don't think we need that extra commit on top.

[oli-obk]

😆 too many reviewers. Seems fine to me to leave out the last commit since this can't happen. We don't re-parse the macro expansion in its context, but instead parse it as an expression.

[compiler-errors]

Drop that commit, squash the rest of the commits into one then r=me

[oli-obk]

@bors r=compiler-errors

[bors]

📌 Commit a183ac6 has been approved by compiler-errors

It is now in the queue for this repository.