unhelpful error message invoking fn foo<T>() when T is not used within signature

[whitequark]

Test case:

fn foo<T>() {}
fn main() { foo() }

Error:

t.rs:2:13: 2:16 error: unable to infer enough type information about `_`; type annotations or generic parameter binding required [E0282]
t.rs:2 fn main() { foo() }
                   ^~~

It should, at least, mention T by name, and I think some rewording would also be beneficial.

[ebfull]

It doesn't matter that T isn't used. This also triggers the error:

fn foo<T>() {
    println!("The size of T is {}", std::mem::size_of::<T>());
}
fn main() { foo() }

At the call site it has to monomorphize foo<T>() but it cannot infer for T. You need to provide foo, at the very least, with a type parameter, like so:

fn foo<T>() {}
fn main() { foo::<usize>() }

[whitequark]

Yes, I understand why this is an error. The point is that the error message is completely unhelpful. I spent at least an hour figuring this out.

[ebfull]

I agree the error message can be improved. I was talking about your title.

#25633 is another example of this.

[nagisa]

Duplicate of #28153