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diff --git a/README.md b/README.md new file mode 100644 index 0000000..b8fa091 --- /dev/null +++ b/README.md @@ -0,0 +1,115 @@ +derive(Display) /// `From<docs>`
+===============
+
+[](https://crates.io/crates/displaydoc)
+[](https://docs.rs/displaydoc)
+
+This library provides a convenient derive macro for the standard library's
+[`core::fmt::Display`] trait.
+
+[`core::fmt::Display`]: https://doc.rust-lang.org/std/fmt/trait.Display.html
+
+```toml
+[dependencies]
+displaydoc = "0.2"
+```
+
+*Compiler support: requires rustc 1.56+*
+
+<br>
+
+### Example
+
+*Demonstration alongside the [`Error`][std::error::Error] derive macro from [`thiserror`](https://docs.rs/thiserror/1.0.25/thiserror/index.html),
+to propagate source locations from [`io::Error`][std::io::Error] with the `#[source]` attribute:*
+```rust
+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,
+}
+
+let error = DataStoreError::Redaction("CLASSIFIED CONTENT".to_string());
+assert!("the data for key `CLASSIFIED CONTENT` is not available" == &format!("{}", error));
+```
+*Note that although [`io::Error`][std::io::Error] implements `Display`, we do not add it to the
+generated message for `DataStoreError::Disconnect`, since it is already made available via
+`#[source]`. See further context on avoiding duplication in error reports at the rust blog
+[here](https://github.com/yaahc/blog.rust-lang.org/blob/master/posts/inside-rust/2021-05-15-What-the-error-handling-project-group-is-working-towards.md#duplicate-information-issue).*
+
+<br>
+
+### Details
+
+- A `fmt::Display` impl is generated for your enum if you provide
+ a docstring comment on each variant as shown above in the example. The
+ `Display` derive macro supports a shorthand for interpolating fields from
+ the error:
+ - `/// {var}` ⟶ `write!("{}", self.var)`
+ - `/// {0}` ⟶ `write!("{}", self.0)`
+ - `/// {var:?}` ⟶ `write!("{:?}", self.var)`
+ - `/// {0:?}` ⟶ `write!("{:?}", self.0)`
+- This also works with structs and [generic types][crate::Display#generic-type-parameters]:
+```rust
+/// oh no, an error: {0}
+#[derive(Display)]
+pub struct Error<E>(pub E);
+
+let error: Error<&str> = Error("muahaha i am an error");
+assert!("oh no, an error: muahaha i am an error" == &format!("{}", error));
+```
+
+- 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.
+
+<br>
+
+### 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](https://github.com/dtolnay/case-studies/blob/master/autoref-specialization/README.md) 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!
+
+
+#### License
+
+<sup>
+Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
+2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
+</sup>
+
+<br>
+
+<sub>
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
+be dual licensed as above, without any additional terms or conditions.
+</sub>
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