Debug Error: `lldb` no such file

[joshualeond]

Thanks for all of the work on this! I’ve tested the new extension on OSX and WSL and it definitely works better than the older version(s). I’m having issues with debugging though, I never tested it with the old extension so not sure if this is just a user error or not.

When I attempt to debug a mojo file I get the following error:

Failed to run preInitCommands commands. See the Debug Console for more details.

Then in the debug console I have:

Running preInitCommands:
(lldb) plugin load $CONDA_PREFIX/lib/libMojoLLDB.*
error: no such file

On OSX I’m seeing basically the same error around this lldb plugin. I haven’t touched the launch.json file yet.

I’d appreciate any tips to get this working.

[AmaranthineCodices]

Hey! This is an issue in how we package Mojo as a Conda package. Are you using the latest nightly version of mojo?

[joshualeond]

Yes I just tested on 0.25.7.0.dev2025092205 and have the same exact error as well.

I've been updating via pixi by keeping mojo = "<1.0.0" in my pixi.toml and running a pixi update to get the latest nightly. The error on OSX prompts me to Open 'launch.json'.

[dafmdev]

I have the same error; I'm using Mojo version 0.25.7.0.dev202510050 via Pixi Conda.

[tool.pixi.dependencies]
modular = ">=25.7.0.dev2025100505,<26"

I have a Mac Pro M1.

Name: Mojo 🔥
Id: modular-mojotools.vscode-mojo
Description: Mojo language support
Version: 26.0.1
Publisher: Modular

If you need more information, please let me know, I don't have much experience creating issues.

[Ahajha]

I believe the latest nightly should have a fix for this, can one of you give it a try?

[dafmdev]

I have the same error.

[tool.pixi.dependencies]
mojo = ">=0.25.7.0.dev2025100705,<0.26"

Running preInitCommands:
(lldb) plugin load $CONDA_PREFIX/lib/libMojoLLDB.*
error: no such file

Name: Mojo 🔥 (nightly)
Id: modular-mojotools.vscode-mojo-nightly
Description: Mojo language support (nightly)
Version: 2025.9.2205
Publisher: Modular
VS Marketplace Link: https://marketplace.visualstudio.com/items?itemName=modular-mojotools.vscode-mojo-nightly

[Ahajha]

@dafmdev It looks like you're using the nightly extension, that's been deprecated in favor of the non-nightly version, which is the one receiving updates.

[dafmdev]

Hello, I share the logs

Running preInitCommands:
(lldb) command script import /Users/danfranco/Documents/test_mojo/.pixi/envs/default/lib/lldb-visualizers/lldbDataFormatters.py
error: module importing failed: This script interpreter does not support importing modules.
(lldb) command script import /Users/danfranco/Documents/test_mojo/.pixi/envs/default/lib/lldb-visualizers/mlirDataFormatters.py
error: module importing failed: This script interpreter does not support importing modules.
Welcome to Mojo debugging! 🔥
Inputs prefixed with a colon are treated as LLDB commands, e.g. `:thread list`. Other inputs are treated as expressions, e.g. `my_struct.some_field`.

Running initCommands:
(lldb) mojo statistics telemetry session.start vscode
error: 'mojo' is not a valid command.
30
Process 55004 exited with status = 0 (0x00000000) 

I am using the following extension

Name: Mojo 🔥
Id: modular-mojotools.vscode-mojo
Description: Mojo language support
Version: 26.0.1
Publisher: Modular
VS Marketplace Link: https://marketplace.visualstudio.com/items?itemName=modular-mojotools.vscode-mojo

mojo --version

Mojo 0.25.7.0.dev2025101405 (81e439c9)

[joshualeond]

Tested again today on the latest mojo nightly builds on WSL (Windows Subsystem for Linux) and I first need to make sure I activate the pixi shell using pixi s and then opening VS code via terminal (code). This gets me much further than when I first opened this issue but unfortunately still not all the way there. I'm now seeing similar errors as @dafmdev mentioned above:

Running preInitCommands:
(lldb) command script import /home/jduncan/datasci/mojo-debug-test/.pixi/envs/default/lib/lldb-visualizers/lldbDataFormatters.py
error: module importing failed: This script interpreter does not support importing modules.
(lldb) command script import /home/jduncan/datasci/mojo-debug-test/.pixi/envs/default/lib/lldb-visualizers/mlirDataFormatters.py
error: module importing failed: This script interpreter does not support importing modules.
Welcome to Mojo debugging! 🔥
Inputs prefixed with a colon are treated as LLDB commands, e.g. `:thread list`. Other inputs are treated as expressions, e.g. `my_struct.some_field`.

Running initCommands:
(lldb) mojo statistics telemetry session.start vscode
error: 'mojo' is not a valid command.
warning: This version of LLDB has no plugin for the language "mojo". Inspection of frame variables will be limited.

I am now able to semi-step through the code using the debugger interface in VS code. However, the watched variables (or really any variable visibility) is still not working:

Could not find type system for language mojo: TypeSystem for language mojo doesn't exist

Lastly, the Step Into results in the following error:

Could not load source 'open-source/max/mojo/stdlib/stdlib/io/io.mojo': Unknown source reference 0.