Incorrect suggestion of private struct members #92999

Lets consider the following code (playground) :

pub struct S {
   pub val: String
}

pub fn test(s: S) {
   dbg!(s.cap)
}

Here, we try to access a property cap on an object of type struct S.
Up to the 1.50 version, the error message was the following :

rror[E0609]: no field `cap` on type `S`
--> <source>:6:12
  |
6 |     dbg!(s.cap)
  |            ^^^ unknown field
  |
 = note: available fields are: `val`

However, since Rust 1.51 and onward, the diagnostic message changed to this:

rror[E0609]: no field `cap` on type `S`
--> <source>:6:12
  |
6 |     dbg!(s.cap)
  |            ^^^ unknown field
  |
 = note: available fields are: `val`
help: one of the expressions' fields has a field of the same name
  |
6 |     dbg!(s.val.vec.buf.cap)
  |            ^^^^^^^^^^^^

While there is indead a cap property on the RawVec struct, this can't be accessed like that, applying the compiler suggestion implies making the buf property of std::vec::Vec public, which is not possible.

The compiler should not look at non-pub properties when searching for properties with a matching name for diagnostic purposes.