fn-ptr docs were not updated for the change to trait impls

[lcnr]

Location

https://doc.rust-lang.org/nightly/std/primitive.fn.html#trait-implementations-1

Summary

we now implement all of these traits for all function pointers. We should change the documentation to mention that.

we may also want to add a dummy impl for rustdoc for https://doc.rust-lang.org/nightly/std/marker/trait.FnPtr.html, similar to

rust/library/core/src/primitive_docs.rs

Lines 1574 to 1583 in 6f8c055

	// Fake impl that's only really used for docs.
	#[cfg(doc)]
	#[stable(feature = "rust1", since = "1.0.0")]
	#[doc(fake_variadic)]
	/// This trait is implemented on function pointers with any number of arguments.
	impl<Ret, T> Clone for fn(T) -> Ret {
	fn clone(&self) -> Self {
	loop {}
	}
	}

[mj10021]

@rustbot claim

[lcnr]

the PR which added the trait was #108080

[mj10021]

Hi @lcnr ! Sorry it took me a bit to get to this after I claimed it. Just want to make sure I'm understanding correctly what the documentation should look like:

All function pointers implement FnPtr, which means they all implement:

ConstParamTy
Destruct
DiscriminantKind
FnPtr
PointerLike
StructuralEq
StructuralPartialEq
Tuple
Unsize
Copy
Send
Sized
Sync
Unpin

(pulled from the FnPtr docs), and so those traits should be included in the function pointer doc? And then would the dummy impl look something like this:

// Fake impl that's only really used for docs.
#[cfg(doc)]
#[unstable(feature = "fn_ptr_trait")]
#[doc(fake_variadic)]
/// This trait is implemented on function pointers with any number of arguments. 
impl<Ret, T> FnPtr for fn(T) -> Ret {
    fn addr(&self) -> *const () {
        // empty
    }
}

[lcnr]

pretty much yeah.

not sure whether it makes sense to differentiate between traits implemented via FnPtr and traits implemented via builtin impls.

I personally don't think we should mention traits which are currently still unstable, that's something we can discuss further after you opened the PR