1# Code Formatting 2 3`bindgen` uses `rustfmt` to format the emitted bindings. This section describes 4how to adjust the `rustfmt` behavior when being used from `bindgen`. 5 6## Passing a `rustfmt.toml` configuration file 7 8`rustfmt` should automatically use any `rustfmt.toml` file that is present in 9the directory from where `bindgen` will be run. If you want to use a 10configuration file that has a different name or that is in a different 11directory you can use the `--rustfmt-configuration-file` flag or the 12[`Builder::rustfmt_configuration_file`](https://docs.rs/bindgen/latest/bindgen/struct.Builder.html#method.rustfmt_configuration_file) 13method. 14 15## Using a nightly release of `rustfmt` 16 17If the `rustfmt` command does not correspond to a nightly release of `rustfmt` 18but you have `rustup` available, you can use `nightly` by following these 19steps: 20 21### When using `bindgen` as a CLI application 22 23Use `rustup run` to run `bindgen`: 24 25```bash 26$ rustup run nightly bindgen [ARGS] 27``` 28 29### When using `bindgen` as a library 30 31Take the output of the following command: 32```bash 33$ rustup which rustfmt --toolchain=nightly 34``` 35and pass it to 36[`Builder::with_rustfmt`](https://docs.rs/bindgen/latest/bindgen/struct.Builder.html#method.with_rustfmt): 37 38```rust,ignore 39use bindgen::Builder; 40use std::process::Command; 41 42fn main() { 43 let output = Command::new("rustup") 44 .args(["which", "rustfmt", "--toolchain", "nightly"]) 45 .output() 46 .expect("Could not spawn `rustup` command"); 47 48 assert!( 49 output.status.success(), 50 "Unsuccessful status code when running `rustup`: {:?}", 51 output 52 ); 53 54 let rustfmt_path = 55 String::from_utf8(output.stdout).expect("The `rustfmt` path is not valid `utf-8`"); 56 57 let bindings = Builder::default() 58 .header("path/to/input.h") 59 .with_rustfmt(rustfmt_path) 60 .generate() 61 .expect("Could not generate bindings"); 62 63 bindings 64 .write_to_file("path/to/output.rs") 65 .expect("Could not write bindings"); 66} 67``` 68 69These two methods also apply to any other toolchain available in your system. 70