This doesn't work the local and type are in different contexts. The old one is the correct way to do this.

That's a bit unfortunate, because removing span_to_remove was kind of the whole purpose of this PR.. I'm the one who added it in #15386

This doesn't work [if] the local and type are in different contexts

Actually, we don't even lint if that's the case:

Or do you think we can instead remove that check now? I tried doing that, then I needed to modfify span_to_remove to be ty.span.with_lo(local.pat.span.source_callsite().hi()), but then all of the following test cases passed at least:

macro_rules! foo {
    () => {
        (a)
    };
};
macro_rules! bar {
    () => {
        _
    };
};

let (a): bar!() = 0;
//~^ let_with_type_underscore
let foo!(): _ = 0;
//~^ let_with_type_underscore
let foo!(): bar!() = 0;
//~^ let_with_type_underscore

gives:

error: variable declared with type underscore
  --> tests/ui/let_with_type_underscore.rs:71:5
   |
LL |     let (a): bar!() = 0;
   |     ^^^^^^^^^^^^^^^^^^^^
   |
help: remove the explicit type `_` declaration
   |
LL -     let (a): bar!() = 0;
LL +     let (a) = 0;
   |

error: variable declared with type underscore
  --> tests/ui/let_with_type_underscore.rs:73:5
   |
LL |     let foo!(): _ = 0;
   |     ^^^^^^^^^^^^^^^^^^
   |
help: remove the explicit type `_` declaration
   |
LL -     let foo!(): _ = 0;
LL +     let foo!() = 0;
   |

error: variable declared with type underscore
  --> tests/ui/let_with_type_underscore.rs:75:5
   |
LL |     let foo!(): bar!() = 0;
   |     ^^^^^^^^^^^^^^^^^^^^^^^
   |
help: remove the explicit type `_` declaration
   |
LL -     let foo!(): bar!() = 0;
LL +     let foo!() = 0;
   |

But:

• the error message mentions _ instead of bar!()
• this could be seen as a feature addition

So I'd say leaving the eq_ctxt in and simplifying span_to_remove is good enough?

Sorry, I meant the pattern and type. e.g. let $name: _

Then maybe that's what the check should've been?