Using a debugger

DISCLAIMER: This is not documentation for the planned debugger support in Zed. Rather, it is intended to provide information on how to use an external debugger while developing Zed itself to both Zed employees and external contributors. Once debugger support is implemented, this section will be updated to provide information on how to use the built-in debugger as part of Zed development.

Build profile considerations

By default, builds using the dev and release profiles (release is the profile used for production builds, i.e. nightly, preview, and stable) include limited debug info.

This is done by setting the profile.(release|dev).debug field in the root Cargo.toml field to "limited".

The official documentation for the debug field can be found here. But the TLDR is that "limited" strips type and variable level debug info.

In release builds, this is done to reduce the binary size, as type and variable level debug info is not required, and does not impact the usability of generated stack traces.

In debug builds, this is done to reduce compilation (especially incremental compilation) time.

However, while the type and variable level debug info is not required for good stack traces, it is very important for a good experience using debuggers, as without the type and variable level debug info, the debugger has no way to resolve local variables, inspect them, format them using pretty-printers, etc.

Therefore, in order to use a debugger to it's fullest extent, you must compile a new Zed binary, with full debug info.

The simplest way to do this, is to use the --config flag to override the debug field in the root Cargo.toml file when running cargo run or cargo build like so:

cargo run --config 'profile.dev.debug="full"'
cargo build --config 'profile.dev.debug="full"'

If you wish to avoid passing the --config flag on every invocation of cargo. You may also change the section in the root Cargo.toml

from

[profile.dev]
debug = "limited"

to

[profile.dev]
debug = "full"

This will ensure all invocations of cargo run or cargo build will compile with full debug info.

WARNING: Make sure to avoid committing these changes!

GDB/LLDB

Background

When installing rust through rustup, (the recommended way to do so when developing Zed, see the documentation for getting started on your platform here) a few additional scripts are installed and put on your path to assist with debugging binaries compiled with rust.

These are rust-gdb and rust-lldb respectively.

You can read more information about these scripts and why they are useful here if you are interested.

However, the summary is that they are simple shell scripts that wrap the standard gdb and lldb commands, injecting the relevant commands and flags to enable additional rust-specific features such as pretty-printers and type information.

Therefore, in order to use rust-gdb or rust-lldb, you must have gdb or lldb installed on your system. If you don't have them installed, you will need to install them in a manner appropriate for your platform.

According to the previously linked article, "The minimum supported debugger versions are GDB 7.7 and LLDB 310. However, the general rule is: the newer the better." Therefore, it is recommended to install the latest version of gdb or lldb if possible.

Note: rust-gdb is not installed by default on Windows, as gdb support for windows is not very stable. It is recommended to use lldb with rust-lldb instead on Windows.

If you are unfamiliar with gdb or lldb, you can learn more about them here and here respectively.

Usage with Zed

Running Zed with a Debugger

After following the steps above for including full debug info when compiling Zed, You can either run rust-gdb or rust-lldb on the compiled Zed binary after building it with cargo build, by running one of the following commands:

rust-gdb target/debug/zed
rust-lldb target/debug/zed

Alternatively, you can attach to a running instance of Zed (such as an instance of Zed started using cargo run) by running one of the following commands:

rust-gdb -p <pid>
rust-lldb -p <pid>

Where <pid> is the process ID of the Zed instance you want to attach to.

To get the process ID of a running Zed instance, you can use your systems process management tools such as Task Manager on windows or Activity Monitor on MacOS.

Alternatively, you can run the ps aux | grep zed command on MacOS and Linux or Get-Process | Select-Object Id, ProcessName in an instance of PowerShell on Windows.

Debugging Panics and Crashes

Debuggers can be an excellent tool for debugging the cause of panics and crashes in all programs, including Zed.

By default, when a process that gdb or lldb is attached to hits an exception such as a panic, the debugger will automatically stop at the point of the panic and allow you to inspect the state of the program.

Most likely, the point at which the debugger stops will be deep in the rust standard library panic or exception handling code, so you will need to navigate up the stack trace to find the actual cause of the panic.

This can be accomplished using the backtrace command in combination with the frame select command in lldb, with similar commands available in gdb.

Once the program is stopped, you will not be able to continue execution as you can before an exception is hit. However, you can jump around to different stack frames, and inspect the values of variables and expressions within each frame, which can be very useful in identifying the root cause of the crash.

You can find additional information on debugging Zed crashes here.