Incorrect error message when accessing private field of union

[gnzlbg]

#[derive(Copy, Clone)]
pub struct B;

mod a {
    pub union U {
        pub a: i32,
        b: crate::B,
    }
}

fn new(a: i32) -> B {
    unsafe { a::U { a }.b }
}

(Playground)

Errors:

    Compiling playground v0.0.1 (/playground)
error[E0616]: field `b` of struct `a::U` is private
  --> src/lib.rs:12:14
   |
12 |     unsafe { a::U { a }.b }
   |              ^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0616`.
error: Could not compile `playground`.

To learn more, run the command again with --verbose.

Notice how it says "struct" when it should say "union".

cc @estebank this looks like low-hanging fruit

[sam09]

Can I pick this up if no-one is working on this?

[estebank]

@sam09 go ahead!

You need to use base_did here

rust/src/librustc_typeck/check/expr.rs

Lines 1394 to 1402 in 5a6d801

	let struct_path = self.tcx().def_path_str(base_did);
	let mut err = struct_span_err!(
	self.tcx().sess,
	expr.span,
	E0616,
	"field `{}` of struct `{}` is private",
	field,
	struct_path
	);

to get whether it is a struct or union using DefKind::descr(DefId).

[sam09]

Thanks @estebank .
Newbie question, but how do I test this while development? Do I build the stage1 compiler and then write a sample test?

[sam09]

#63982

[estebank]

@sam09 ./x.py build src/test/ui -i --stage 1 --keep-stage 1 --bless is the way to get the fastest iteration time. --keep-stage 1 is theoretically suspect but should affect you on what you're working on and -i is marginally slower on first compile but much faster on subsequent compiles. You rarely (if ever) need --stage 2.