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.

[joshuataylor]

Seeing this with Strings on rustc 1.83.0-nightly (1d68e6dd1 2024-09-21), last build that worked was rustc 1.82.0-nightly (41dd149fd 2024-08-11).

I'm seeing this in RustRover, tried in VSCode and came across this issue.

Doesn't happen with stable (rustc 1.81.0 (eeb90cda1 2024-09-04)).

rust-lldb seems to work fine though.

Test file setup

src/main.rs:

fn main() {
    let b = String::from("hello!");
    println!("Hello, world!");
}

Run rust-lldb

cargo build

How to use rust-lldb

One liner:

rust-lldb --batch -o "breakpoint set --file main.rs --line 3" -o "run" -o "v b" ./target/debug/testd

Otherwise:

rust-lldb target/debug/testd

1. Set a breakpoint

breakpoint set --file main.rs --line 3

2. Run the program

run

3. View the breakpoint

v b

4. Expected output:

(alloc::string::String) b = "hello!" {
  vec = size=6 {
    [0] = 'h'
    [1] = 'e'
    [2] = 'l'
    [3] = 'l'
    [4] = 'o'
    [5] = '!'
  }
}

lldb_providers

It might be an issue with lldb_providers, these show the formatted output.

1. lldb_providers.py
2. rust_types.py

[alebairos]

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.

yep. Reproduced here. Days to find out when I finally switched back to stable.

stable-x86_64-unknown-linux-gnu unchanged - rustc 1.81.0 (eeb90cd 2024-09-04)
nightly-x86_64-unknown-linux-gnu unchanged - rustc 1.83.0-nightly (14f303b 2024-10-04)

[mschnell1]

I don't know if this is related anyhow....
Debugging issue,. when debugging using VSCode (I suppose I have all current versions, and stable rustc).
I have code with variable name overriding (multiple let xyz= .... e.g. let xy = fxy(); let xy = xy.unwrap(); )
The debugger mostly shows the value of the first occurrence of a variable (-name) and not the one in scope with the breakpoint. (Of course the outdated content often is overridden at that point and just rubbish)