“cannot initialize a tuple struct which contains private fields” with no tuple struct involved

[kpreid]

Code

struct Foo {}
struct Bar {}

impl Foo {
    fn into_bar(self) -> Bar {
        Bar(self)
    }
}

Current output

error[E0423]: cannot initialize a tuple struct which contains private fields
 --> src/lib.rs:6:9
  |
6 |         Bar(self)
  |         ^^^
  |
  = note: constructor is not visible here due to private fields

Desired output

error[E0423]: expected function, tuple struct or tuple variant, found struct `Bar`
 --> src/lib.rs:6:9
  |
6 |         Bar(self)
  |         ^^^

Rationale and extra context

The message is incorrect in two ways:

• Bar is not a tuple struct
• Bar has no private fields

It appears that something is making too many assumptions about why a tuple struct constructor might not be visible at a specific call site.

Other cases

The incorrect diagnostic only occurs for Bar(self), and not when a normal variable is used in place of self. It also seems like sometimes the correct error is printed, nondeterministically, but I have not found consistent reproduction conditions.

Rust Version

rustc 1.93.0-nightly (01867557c 2025-11-12)
binary: rustc
commit-hash: 01867557cd7dbe256a031a7b8e28d05daecd75ab
commit-date: 2025-11-12
host: aarch64-apple-darwin
release: 1.93.0-nightly
LLVM version: 21.1.5

Anything else?

@rustbot label +regression-from-stable-to-nightly

[Paladynee]

smaller, reproduced on rustc 1.93.0-nightly (25d319a0f 2025-11-11):

struct Bar {}
impl Bar {
    fn into_self(self) -> Bar {
        Bar(self)
    }
}

[apiraino]

bisection seems to point to dd31609

cc @davidtwco @Jamesbarford