Question 1

How do I install cargo expand and set up rustfmt?

Accepted Answer

Install cargo-expand with `cargo install cargo-expand` and rustfmt with `rustup component add rustfmt`. This ensures formatted output for better readability, as outlined in the Installation section.

Question 2

cargo expand vs using cargo rustc directly: which is better for debugging macros?

Accepted Answer

cargo-expand is better because it wraps the verbose `cargo rustc --profile=check -- -Zunpretty=expanded` command into a simple interface with rustfmt integration and syntax highlighting, making the output more user-friendly and readable.

Question 3

How to expand only a specific function or module with cargo expand?

Accepted Answer

Use `cargo expand path::to::module` or similar syntax to target specific parts. This is useful for focusing on relevant code without cluttering the output, as mentioned in the Options section.

Question 4

Why does the expanded code from cargo expand sometimes not compile?

Accepted Answer

Due to macro hygiene and lossy expansion, the text output might not be accurate for compilation. The tool is intended for debugging, not as a source of compilable code, as explained in the Disclaimer.

Question 5

Can cargo expand help identify hygiene issues in macros?

Accepted Answer

Yes, by showing the expanded code, it can reveal how macros interact with variables and scopes, but as noted in the disclaimer, it's not foolproof and should be used with caution for such cases.

Question 6

How to change the syntax highlighting theme in cargo expand?

Accepted Answer

Configure the theme in `~/.cargo/config.toml` under the `[expand]` section with `theme = "ThemeName"`. Run `cargo expand --themes` to see available options, as described in the Configuration.

cargo-expand

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