How do I inspect local variables or use the watch window with Rust code using VSCode and LLDB?

lldb doesn't "real" have support for Rust. It uses the C++ type system to support Rust types, and uses the C++ expression parser for expressions. So while simple things should work, more complex language features aren't well supported by "rust as C++".

It's possible to add language support for languages not directly supported by the clang front-end to lldb (see for instance the Go & OCaml support).

Tom Tromey is working on an actual Rust port for lldb, see: https://archive.fosdem.org/2018/schedule/event/rustdebug/ where he discusses this project, for instance. He hasn't submitted the results to mainline lldb yet, but his fork is available at https://github.com/rust-lang-nursery/lldb/commits/rust if anybody interested in Rust debugging in lldb wants to lend a hand.

This is for Windows users.

First, you'd try to install LLVM as suggestion above:

Install LLVM https://github.com/llvm/llvm-project/releases/tag/llvmorg-18.1.8

Install Cygwin https://cygwin.com/

rustup component add rust-src rust-analysis rust-lldb

Then, switch to GNU Tool chain:

rustup install stable-x86_64-pc-windows-gnu
rustup default stable-x86_64-pc-windows-gnu

When you cargo build, you'd quickly run into errors for example:

C:/gcc/bin/../x86_64-w64-mingw32/bin/ld.exe: cannot find -lgcc_eh: No such file or directory
collect2.exe: error: ld returned 1 exit status

Depends on what you included in Cargo.toml, you may have many more errors.

To fix:

Option 1. you can revert to MSVC toolchain:

rustup default stable-x86_64-pc-windows-msvc
                    

However, you'd be back to square one: What you see in VSCode Watch Window is still Jibberish

Option 2. Install Cygwin

https://www.mingw-w64.org/downloads/

Add C:\cygwin64\bin to PATH

Then switch to GNU Tool chain, try cargo build. Does it works? Remember "Select Packages", choose all gcc's related and install source as well.

• gcc-core
• gcc-debuginfo
• mingw64-x86*

If installer complains file corrupted or mirror don't have package you need, choose another mirror and try again.

Suggest:

• https://mirrors.kernel.org/
• https://cygwin.mirror.constant.com/

Also, in the Select Packages window, search for openssl and openssl-debuginfo. Install the following packages from the Libs and Devel categories:

• libopenssl-devel
• libopenssl100 or libopenssl3

If you can't find a package from cygwin mirror, try Msys2. For example, I can't find libopenssl-dev, libopenssl100, or libopenssl3 from any of the mirror, I used Msys2 to finish the job.

pacman -S mingw-w64-x86_64-openssl mingw-w64-x86_64-pkg-config

Option 3. Install Msys2 https://www.msys2.org/

PATH should point to C:\msys64

Bring up MSYS2 command prompt: clang32.exe

Update package manager:

pacman -Syu
                            

Install MinGW-W64:

pacman -S mingw-w64-x86_64-gcc mingw-w64-x86_64-gdb
pacman -S mingw-w64-x86_64-gcc
pacman -S mingw-w64-i686-gcc
pacman -S mingw-w64-x86_64-openssl mingw-w64-x86_64-pkg-config
pacman -S mingw-w64-x86_64-zstd

Now, to remove a package:

pacman -Rns mingw-w64-x86_64-zstd

And again, if you can't find a package in msys2, go back to cygwin and see if you can find it in one of the mirrors.

And in the end, I managed to cargo build, F5/Debug from VSCode on my windows laptop AND FINALLY be able see my variables and their values from Watch window!!!

Overall this been a very painful process. Hope this will help.

Fyi, I still can't resolve one problem

solana-client = "2.0.13"  <-- Bad
solana-sdk = "2.0.13" <-- OK

Problem:

cargo:warning=zstd/lib/compress\zstd_compress_literals.c:14:10: fatal error: zstd_compress_literals.h: No such file or directory
     14 | #include "zstd_compress_literals.h"
        |          ^~~~~~~~~~~~~~~~~~~~~~~~~~

I am an engineer/trader. I think I have better things to do.

Fyi, launch.json

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "lldb",
            "request": "launch",
            "name": "Debug siglib_rs",
            "program": "${workspaceFolder}/target/debug/myapp",
            "preLaunchTask": "cargo build",
            "cargo": {
                "args": ["build"],
                "filter": {
                    "name": "myapp",
                    "kind": "bin"
                }
            },
            "args": [],
            "cwd": "${workspaceFolder}"
        }
    ]
}

Also when you're installing so many things, you may blow your c-drive. Check what's eating up disk space you need wsl, and du command.

C:\Users\xxx\AppData
wsl
du -h /mnt/c/Users/xxx/AppData/Local --max-depth=2

Also, fyi, ... a few weeks later, with GNU Tool Chain: The experience for Windows users is just terrible.

Final Solution

Out of desperation, I found this. And decided to try C/C++ Extension with MSVC toolchain

And from launch.json (type from lldb to cppvsdbg):

{
    "version": "0.2.0",
    "configurations": [
      {
        "type": "cppvsdbg",
        "request": "launch",
        "name": "Debug executable 'rust'",
        "program": "${workspaceFolder}/target/debug/rust.exe",
        "args": [],
        "cwd": "${workspaceFolder}",
        "environment": [],
        "console": "integratedTerminal",
        "preLaunchTask": "cargo build"
      }
    ]
  }

And tasks.json (For preLaunchTask):

{
    "version": "2.0.0",
    "tasks": [
      {
        "label": "cargo build",
        "type": "shell",
        "command": "cargo",
        "args": ["build"],
        "group": {
          "kind": "build",
          "isDefault": true
        },
        "problemMatcher": ["$rustc"]
      }
    ]
  }
  

Then everything worked again!!