What is the difference between anyhow and thiserror

Use anyhow for top-level error handling in binaries and thiserror for defining custom error types in libraries. anyhow provides a flexible Result<T, anyhow::Error> that erases error types, while thiserror generates impl std::error::Error for your custom structs via the #[derive(thiserror::Error)] macro. In the mdbook-trpl project, anyhow is used for the Result type in functions like rewrite_figure, while thiserror defines the CompositeError and Error structs in src/lib.rs and src/config/mod.rs.

Think of anyhow as a universal wrapper that catches any error so you don't have to name them all, perfect for the main entry point of your program. thiserror is a tool that lets you create your own specific error types with clear names, which is essential when you are building a library for others to use. You typically use anyhow to handle errors at the end of your program and thiserror to define the errors your program or library produces.