Forgetting to call a variant constructor causes a confusing error message

[arielb1]

STR

struct Foo(u32);

fn test() -> Foo { Foo }

fn main() {
}

Confusing result

error[E0308]: mismatched types
 --> <anon>:3:20
  |
3 | fn test() -> Foo { Foo }
  |                    ^^^ expected struct `Foo`, found fn item
  |
  = note: expected type `Foo`
  = note:    found type `fn(u32) -> Foo {Foo::{{constructor}}}`

[arielb1]

The error message mentions function items, which is confusing to new users.

[estebank]

non-fn-like structs have better output, we should perform the same for fn-like structs:

error[E0423]: expected value, found struct `Bar`
 --> src/main.rs:9:21
  |
9 | fn test2() -> Bar { Bar }
  |                     ^^^ did you mean `Bar { /* fields */ }`?

[estebank]

Mentoring instructions:

In note_type_err, check wether values can be decomposed into Some(ValuePairs::Types(exp_found). If it can, check wether exp_found.found is a TypeVariant::TyFnPtr(_) with an FnSig.output() == exp_found.expected. If that is the case, add a note to the diag like for E-423.

[colinmarsh19]

Has anyone worked on this recently? I might take a crack at it. New to Rust but I'd like to learn, and start getting involved with OSS. Let me know if there are any conflicts, or if anyone is able to give me some guidance. Thanks! :)

[estebank]

@colinmarsh19 go ahead!

The terse explanation above should give enough context for someone slightly familiar with the compiler, but if you need more help you can always reach out with a comment in this ticket, on gitter or by creating a PR for us to comment on your code directly.

[joshleeb]

@colinmarsh19 are you currently working on this? If not I would like to give it a go :)

[dsheets]

I believe this issue has been fixed in #45630.