1.3. Debugging Rust Programs

Debugging is a crucial skill you should learn (if you don’t know yet) in order to become a more effective software developer. If you write software, your software will contain bugs. Debugging is the process of finding those bugs, which is necessary if you want to fix them.

1.3.1. Debuggers

There are tools to help you debug software called debuggers. You may have already heard about these. For example, in the C, C++ world, gdb and lldb are two popular debuggers. gdb is used to debug programs that have been compiled with gcc, while lldb is used to debug programs compiled with the LLVM toolkit. What this means in practice, in 2020, is that if you work on a Linux platform, you’ll likely be using gdb. If you work on a Mac OS platform, you’ll likely be using lldb. If you work on a windows platform, then you may be using either one, depending on your configuration.

1.3.2. Debuggers in the IDE

A popular way of writing software is via IDEs (which we recommend you use to develop crustyDB). IDEs for most languages come with a debugger preconfigured. The situation for Rust is a little different. Only relatively recently IDE developers have started incorporating debuggers for Rust, and the support is still sparse. If you use Visual Studio Code (a lightweight and open source IDE), you will be able to use a Rust debugger (based on gdb or lldb depending on the underlying platform). You can easily find instructions online on how to set this up.

Most other free IDEs do not have good support for the Rust debugger yet.

CLion

JetBrain’s CLion IDE looks to have a solid Rust debugger with the Rust extension. However CLion is not free, but it does offer academic licenses. Apply here if you want to access the tool (some restrictions on what you can use the tool for). Here are instructions on set up and using which worked for me out of the box on Ubuntu (with installing the Rust plugin). One of our TAs uses CLion to debug Rust on OSX. The link also contains instructions for debugging on Windows, but it has not been tested by us.

VSCode

We have had some mixed success with using VSCode for debugging Rust (although it is a great Rust IDE with the right extensions). Using the extensions rust-analyzer and CodeLLDB on Ubuntu has gotten debugging working on a set up. We included the launch.json for running tests in a package.

1.3.3. Alternative ways of debugging programs

You are already familiar with printing the values of variables in your programs in order to understand program behavior and detect problems, i.e., in order to debug your programs. Rust has its own println!() macro (and Crusty uses a logging library). Rust also has a dbg!() macro in its standard library, which will simply format the argument so its printable along with the line where it’s found. A real debugger will give you much more information, presented better, and in context, so it’s a much more powerful way of debugging programs, and the recommended way. However, in some instances, the macros above may come in handy, especially as Rust’s debuggers support matures.