Name of enum variant with fields is suggested in error messages

[Aaron1011]

The following code:

enum MyEnum {
    First(bool),
    Second
}

fn main() {
    MyEnum.foo();
}

gives the following error message

error[E0423]: expected value, found enum `MyEnum`
 --> src/main.rs:7:5
  |
7 |     MyEnum.foo();
  |     ^^^^^^
  |
help: try using one of the enum's variants
  |
7 |     MyEnum::First.foo();
  |     ^^^^^^^^^^^^^
7 |     MyEnum::Second.foo();
  |     ^^^^^^^^^^^^^^

MyEnum::First.foo() calls foo on a function pointer (the constuctor function for MyEnum::First, which is almost never what you want.

At the very least, we should not be suggesting using enum variants that have associated data. When attempting to call a method on the base enum type, we might want to suggest using :: instead (e.g. MyEnum::First::foo()), which is more likely to be what the user wants.

[cofibrant]

@rustbot claim

[Alexendoo]

Triage: Hi, are you still working on this issue @doctorn?

[Alexendoo]

@rustbot release-assignment