Suboptimal error message when matching on a tuple struct using a private constructor

[JarredAllen]

Code

pub mod foo {
    pub struct Foo(u8);
}

pub fn bar(foo: Option<foo::Foo>) {
    match foo {
        // Some(foo::Foo{..}) => println!("Foo"),
        Some(foo::Foo(..)) => println!("Foo"),
        None => println!("No Foo"),
    }
}

Current output

Compiling playground v0.0.1 (/playground)
error[E0603]: tuple struct constructor `Foo` is private
 --> src/lib.rs:8:19
  |
2 |     pub struct Foo(u8);
  |                    -- a constructor is private if any of the fields is private
...
8 |         Some(foo::Foo(..)) => println!("Foo"),
  |                   ^^^ private tuple struct constructor
  |
note: the tuple struct constructor `Foo` is defined here
 --> src/lib.rs:2:5
  |
2 |     pub struct Foo(u8);
  |     ^^^^^^^^^^^^^^^^^^^
help: consider making the field publicly accessible
  |
2 |     pub struct Foo(pub u8);
  |                    +++

For more information about this error, try `rustc --explain E0603`.
error: could not compile `playground` (lib) due to 1 previous error

Desired output

Compiling playground v0.0.1 (/playground)
error[E0603]: tuple struct constructor `Foo` is private
 --> src/lib.rs:8:19
  |
2 |     pub struct Foo(u8);
  |                    -- a constructor is private if any of the fields is private
...
8 |         Some(foo::Foo(..)) => println!("Foo"),
  |                   ^^^ private tuple struct constructor
  |
note: the tuple struct constructor `Foo` is defined here
 --> src/lib.rs:2:5
  |
2 |     pub struct Foo(u8);
  |     ^^^^^^^^^^^^^^^^^^^
help: consider making the field publicly accessible
  |
2 |     pub struct Foo(pub u8);
  |                    +++
help: consider matching via `{ .. }` braces instead of the constructor
  |
8 |         Some(foo::Foo { .. }) => println!("Foo")
  |                       ++++++

For more information about this error, try `rustc --explain E0603`.
error: could not compile `playground` (lib) due to 1 previous error

Rationale and extra context

I've used Rust for a while, and I just discovered that this is an option that lets you match on tuple structs with private fields. It would be great if the compiler could recommend this as a solution.

Other cases

If the `foo::Foo` comes from an external dependency, it does not suggest making the field publicly accessible (makes sense, since you likely can't change the dependency), but no suggestions are provided. I think it's more important to include my proposed new help text in that case, so a solution is provided, but still net beneficial in the above case.

Rust Version

Using [the Playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021)'s current nightly release:

1.80.0-nightly (2024-04-29 a8a1d3a771850e1e364e)

(sorry, I don't know how to get the playground to show the full verbose version output)

Anything else?

No response

[workingjubilee]

hm. It's not clear to me why the version you initially went with isn't permitted.

[JarredAllen]

hm. It's not clear to me why the version you initially went with isn't permitted.

I'm not an expert, so I might be wrong, but my guess is that falls out from it being a minor SemVer change to convert between tuple and normal structs if all fields are private.

[workingjubilee]

That seems plausible. The usual semantic of .. in this case is to ignore all other subfields, however, so I guess what I'm really asking is why we can't match on structs with Struct(..) in general.

[workingjubilee]

I suppose we could want some immediately-adjacent syntactic space for variadics that would block off this being a logical conclusion.