Debug variables pane can't see through Rust Rc and friends

[Andrew-Fryer]

Is there any way to see what data is on the other side of a Rust Rc or Weak pointer during debugging?

I haven't been able to find a way to cast the pointers in the debug console and the variables pane shows the number of strong and weak references, but not the actual data that is being referenced.

It seems that a view of the actual data should be generated here:
https://github.com/vadimcn/vscode-lldb/blob/a5e1f40b40cc2a61d04c237a75330e6aa4b4e2c3/formatters/rust.py#L451
However, this line doesn't produce anything that obj_summary understands:
https://github.com/vadimcn/vscode-lldb/blob/a5e1f40b40cc2a61d04c237a75330e6aa4b4e2c3/formatters/rust.py#L421

[vadimcn]

Evaluating Rc<T> in the debug console should display a structural tree view of T. Got any examples of what isn't working?

[Andrew-Fryer]

Thanks for the fast reply!

Sorry I didn't make a MWE first.
I'm working on that now and discovered it works much much better than I thought.
I've narrowed down most of my issues to trait objects. Is there any way to see which implementation of a trait is behind a Box<dyn MyTrait>?

I'm still working on an MWE what seems to be a separate issue. I suspect that trait objects in enums prevent the enum from being represented in the variable pane properly. I'll send a MWE when I have one...

[Andrew-Fryer]

It turns out that most of the time I'm using Rc, the pointer is to a trait object.

Here's the simplest example of the Variables pane not seeing through trait objects.

let mut test: Box<dyn fmt::Display> = Box::new(5);
test = Box::new(87.5); // without this line, we can see through `test`; with this line, we can't

Is it possible to see the underlying data in the Debug console?

The other cases I was using Rc, the pointer is to an enum that caused issues for some reason.
Here's the simplest example I can produce:

use std::rc::{Rc, Weak};

pub struct Container {
    contents: Weak<Container>,
}

fn main() {
    let d = Container {
        contents: Weak::new(),
    };
    let d_rc = Rc::new(d);
    // now, we can see through `d`, but not `d_rc`
    println!("Hello, world!"); // I put my breakpoint on this line
}

Perhaps this is related to #827 ?

I'm running Ubuntu 22.04.2 LTS, rustc 1.55.0, vscode: code 1.76.0, vadimcn.vscode-lldb-1.8.1

[billti]

I'm hitting a similar issue trying to see into Rc for a str being referenced. See below for a clipping of how the local variable is expanding. ('xx' is expanding similarly)

I don't know if you copy the rust-lldb helpers, but trying it there gives slightly similar behavior. (It only shows the value 'B' instead of the Rc'ed string - and 66 (which CodeLLDB is showing) is the ASCII code for 'B'.

(lldb) var
(&str) my_name = "Bill" {
  data_ptr = 0x00000001000365dc "Billline"
  length = 4
}
(rsenum::Testing) foo = {
  name = strong=2, weak=0 {
    value = 'B'
  }
  other_name = "Bill" {
    vec = size=4 {
      [0] = 'B'
      [1] = 'i'
      [2] = 'l'
      [3] = 'l'
    }
  }
}
(alloc::rc::Rc<unsigned char>) xx = strong=2, weak=0 {
  value = 'B'
}
(lldb) version

[billti]

FYI: Logged in the Rust repo as rust-lang/rust#114195