This post is from a series of posts about writing a small application in Rust to display information about a particular git repository.

• Part 1: Writing MVP

Yesterday I finished with a reasonably good starting point and I thought that I would not talk about diagnostics, but after finding out how good rust tool-chain is at this, I wanted to share some thoughts.

Yes, some simple CLIs like ours probably don’t need an option to do heavy diagnostics on it. However, when we do run into problems and don’t have a good way to introspect your programs, I am going to waste more time than I want. That is why it makes sense to start doing it as early as possible.

Macros to the rescue

Using the tips from rust cookbook one can get started really quickly. Add the following to the dependency section in your Cargo.toml:

log = "0.4"
env_logger = "0.5"

and run:

$ cargo update

Then follow the instructions to get the env_logger set up.

Then you can enable debug logging for your own program by simply running like:

$ RUST_LOG=git_prompt cargo run -- ${YOUR_PATH_TO_GIT_REPO}

If you want all logs, including other packages, you can do this by:

$ RUST_LOG=debug cargo run -- ${YOUR_PATH_TO_GIT_REPO}

This gives you all the logs from all the packages and the compiler. This can be really useful tricky situations, which I am probably not going to encounter here, but it will definitely useful in the future.

Things I really like:

• debug! and other related macros can do really clever stuff in order to limit the impact of the logging.
• standard way to do logging through macros.
• not requiring to do dependency injection for logging. It is a cross-cutting concern and as a result it may pollute your object factory functions.

Continue to:

• Part 3: generating test data
• Part 4: type driven rewrite