Crate displaydoc

This library provides a convenient derive macro for the standard library’s core::fmt::Display trait.

[dependencies]
displaydoc = "0.2"

Compiler support: requires rustc 1.31+

Example

use std::io;
use displaydoc::Display;
use thiserror::Error;

#[derive(Display, Error, Debug)]
pub enum DataStoreError {
    /// data store disconnected
    Disconnect(#[source] io::Error),
    /// the data for key `{0}` is not available
    Redaction(String),
    /// invalid header (expected {expected:?}, found {found:?})
    InvalidHeader {
        expected: String,
        found: String,
    },
    /// unknown data store error
    Unknown,
}

Details

• A Display impl is generated for your type if you provide doc comment messages on the struct or each variant of your enum, as shown above in the example.

  The messages support a shorthand for interpolating fields from the error.

  • /// {var} ⟶ write!("{}", self.var)
  • /// {0} ⟶ write!("{}", self.0)
  • /// {var:?} ⟶ write!("{:?}", self.var)
  • /// {0:?} ⟶ write!("{:?}", self.0)

• Two optional attributes can be added to your types next to the derive:

  • #[ignore_extra_doc_attributes] makes the macro ignore any doc comment attributes (or /// lines) after the first. Multi-line comments using /// are otherwise treated as an error, so use this attribute or consider switching to block doc comments (/** */).

  • #[prefix_enum_doc_attributes] combines the doc comment message on your enum itself with the messages for each variant, in the format “enum: variant”. When added to an enum, the doc comment on the enum becomes mandatory. When added to any other type, it has no effect.

• In case you want to have an independent doc comment, the #[displaydoc("...") atrribute may be used on the variant or struct to override it.

FAQ

1. Is this crate no_std compatible?

   • Yes! This crate implements the core::fmt::Display trait not the std::fmt::Display trait so it should work in std and no_std environments. Just add default-features = false.

2. Does this crate work with Path and PathBuf via the Display trait?

   • Yuuup. This crate uses @dtolnay’s autoref specialization technique to add a special trait for types to get the display impl, it then specializes for Path and PathBuf and when either of these types are found it calls self.display() to get a std::path::Display<'_> type which can be used with the Display format specifier!

Derive Macros

Display

Derive macro for implementing Display via doc comment attributes