Module snafu::guide::attributes

Attributes understood by the Snafu macro

Controlling Display

There are a number of ways you can specify how the Display trait will be implemented for each variant:

• #[snafu(display("a format string with arguments: {}", info))]

  The argument is a format string and the arguments. Available in Rust 1.34.

• #[snafu(display = r#"("a format string with arguments: {}", info)"#)]

  The same argument as above, but wrapped in a raw string to support previous Rust versions.

Each choice has the same capabilities. All of the fields of the variant will be available and you can call methods on them, such as filename.display().

Controlling visibility

By default, each of the context selectors and their inherent methods will be private. It is our opinion that each module should have one or more error types that are scoped to that module, reducing the need to deal with unrelated errors when matching and increasing cohesiveness.

If you need access the context selectors from outside of their module, you can use the #[snafu(visibility)] attribute. This can be applied to the error type as a default visibility or to specific context selectors.

There are a number of forms of the attribute:

• #[snafu(visibility(X))]

  X is a normal Rust visibility modifier (pub, pub(crate), pub(in some::path), etc.). Supported in Rust 1.34.

• #[snafu(visibility = "X")]

  The same argument as above, but wrapped in a string to support previous Rust versions.

• #[snafu(visibility)] will reset back to private visibility.

#[derive(Debug, Snafu)]
#[snafu(visibility = "pub(crate)")] // Default
enum Error {
    IsPubCrate, // Uses the default
    #[snafu(visibility)]
    IsPrivate,  // Will be private
}

Controlling backtraces

If your error contains other SNAFU errors which can report backtraces, you may wish to delegate returning a backtrace to those errors. Use #[snafu(backtrace(delegate))] to specify this:

#[derive(Debug, Snafu)]
enum Error {
    MyError {
        #[snafu(backtrace(delegate))]
        source: another::Error,
    }
}