How to format a `TokenStream` with rustfmt?

1

I have generated some code with proc_macro2 and want to format it and write it to a file at a specified path. How should I do this? Inputting the string directly into rustfmt::format_input raises an error.

2

What error, specifically?

3

I just forget... Related with the "terminal"? Anyway it was weird.

4

Piping into stdin should work fine. It's what I've used before to clean up the output from a code generator.

I'm guessing the code you generated had a syntax error, and rustfmt wasn't able to recover from it.

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5

Finally I just write original tokenstream.to_string() to the dest file and then assert!(Command::new("rustfmt").arg(&path).status().unwrap().success());.

The error was failed to emit error: operation not supported by the terminal. Code below:

fn main() {
    let ibuf = something_outputs_tokenstream().to_string();
    let mut obuf = Vec::new();
    let mut ocur = std::io::Cursor::new(&mut obuf);
    let _ = rustfmt::format_input(rustfmt::Input::Text(ibuf), &Default::default(), Some(&mut ocur)).unwrap();
    println!("{}", String::from_utf8(obuf).unwrap());
}

Calling the CLI's rustfmt has never presented any problems.

6

Yeah, rustfmt is not designed to be a "public" Rust library crate; only a CLI binary.

For machine-generated output,

https://lib.rs/prettyplease

can be used as a Rust library and generates, in general, less weirdly formatted code (since machine-generated code can get weird, sometimes, and rustfmt was not made to account for such atypical cases in mind).

3 Likes
7

Thanks, it works well.

8

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