Unable to read value of recursive enum when debugging with lldb

[clems4ever]

Hello,

I'm currently facing an issue preventing me from debugging some code where recursive enums are involved. I cannot read the value from the debugger (LLDB using the extension from Vadim Chugunov on VSCode), instead I get the following error message in vscode: "<error: invalid value object>". Other types are readable, even non-recursive enums.

A picture is worth a thousand words so here it is:

The code to reproduce is simple:

#[derive(Debug)]
enum Test{
    Test(Box<Test>),
    Tail
}

fn main() {
    let t = Test::Test(Box::new(Test::Tail));

    println!("{:?}", t);
}

Ideally, I would be able to troubleshoot the content of the variable.

Here is the version of rust I'm using:

$ rustc --version --verbose
rustc 1.74.0 (79e9716c9 2023-11-13)
binary: rustc
commit-hash: 79e9716c980570bfd1f666e3b16ac583f0168962
commit-date: 2023-11-13
host: x86_64-unknown-linux-gnu
release: 1.74.0
LLVM version: 17.0.4

I have the same problem with the nightly

$ rustc --version --verbose
rustc 1.76.0-nightly (37b2813a7 2023-11-24)
binary: rustc
commit-hash: 37b2813a7be580ef59048a6bd08444c79e5cc97f
commit-date: 2023-11-24
host: x86_64-unknown-linux-gnu
release: 1.76.0-nightly
LLVM version: 17.0.5

I think this might not be a bug but rather a use case not yet properly handled by rust and/or lldb. Does anyone know?

Thanks in advance.

[GuyResh]

Same issue with VecDeque:
{...}
: <error: invalid value object>
...
[raw] alloc::collections::vec_deque::VecDeque<u64,alloc::alloc::Global>

[vlovich]

Seeing this as well. The VecDequeu issue is particularly bad since it's a std library container.

[8thMage]

I tracked down the issue to this change:
502df1b
Where the capacity is no longer stored as a usize, but it's stored as a pointer.

code lldb rust didn't handle it, and the change is easy from:
self.cap = gcm(self.valobj, 'buf', 'cap').GetValueAsUnsigned()
to:
self.cap = gcm(self.valobj, 'buf', 'cap', "0").GetValueAsUnsigned()
I'll create a pull request.

[incapdns]

The same thing is happening to me, can anyone tell me if there is any workaround or if it is also happening in the stable version?

[mschnell1]

The problem still persists. With the current nightly build I get the message <error: invalid value object>, while with the stable build the content of the vector is shown.

[elenakrittik]

@mschnell1 See vadimcn/codelldb#1142. I don't know if it's a CodeLLDB or Rust issue, though.