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// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
// https://github.com/unicode-org/icu4x/blob/main/documents/process/boilerplate.md#library-annotations
#![cfg_attr(all(not(test), not(doc)), no_std)]
#![cfg_attr(
not(test),
deny(
clippy::indexing_slicing,
clippy::unwrap_used,
clippy::expect_used,
clippy::panic,
clippy::exhaustive_structs,
clippy::exhaustive_enums,
missing_debug_implementations,
)
)]
//! `writeable` is a utility crate of the [`ICU4X`] project.
//!
//! It includes [`Writeable`], a core trait representing an object that can be written to a
//! sink implementing `std::fmt::Write`. It is an alternative to `std::fmt::Display` with the
//! addition of a function indicating the number of bytes to be written.
//!
//! `Writeable` improves upon `std::fmt::Display` in two ways:
//!
//! 1. More efficient, since the sink can pre-allocate bytes.
//! 2. Smaller code, since the format machinery can be short-circuited.
//!
//! # Examples
//!
//! ```
//! use std::fmt;
//! use writeable::assert_writeable_eq;
//! use writeable::LengthHint;
//! use writeable::Writeable;
//!
//! struct WelcomeMessage<'s> {
//! pub name: &'s str,
//! }
//!
//! impl<'s> Writeable for WelcomeMessage<'s> {
//! fn write_to<W: fmt::Write + ?Sized>(&self, sink: &mut W) -> fmt::Result {
//! sink.write_str("Hello, ")?;
//! sink.write_str(self.name)?;
//! sink.write_char('!')?;
//! Ok(())
//! }
//!
//! fn writeable_length_hint(&self) -> LengthHint {
//! // "Hello, " + '!' + length of name
//! LengthHint::exact(8 + self.name.len())
//! }
//! }
//!
//! let message = WelcomeMessage { name: "Alice" };
//! assert_writeable_eq!(&message, "Hello, Alice!");
//!
//! // Types implementing `Writeable` are recommended to also implement `fmt::Display`.
//! // This can be simply done by redirecting to the `Writeable` implementation:
//! writeable::impl_display_with_writeable!(WelcomeMessage<'_>);
//! ```
//!
//! [`ICU4X`]: ../icu/index.html
extern crate alloc;
mod cmp;
#[cfg(feature = "either")]
mod either;
mod impls;
mod ops;
mod parts_write_adapter;
mod testing;
mod try_writeable;
use alloc::borrow::Cow;
use alloc::string::String;
use core::fmt;
pub use try_writeable::TryWriteable;
/// Helper types for trait impls.
pub mod adapters {
use super::*;
pub use parts_write_adapter::CoreWriteAsPartsWrite;
pub use try_writeable::TryWriteableInfallibleAsWriteable;
pub use try_writeable::WriteableAsTryWriteableInfallible;
}
#[doc(hidden)]
pub mod _internal {
pub use super::testing::try_writeable_to_parts_for_test;
pub use super::testing::writeable_to_parts_for_test;
}
/// A hint to help consumers of `Writeable` pre-allocate bytes before they call
/// [`write_to`](Writeable::write_to).
///
/// This behaves like `Iterator::size_hint`: it is a tuple where the first element is the
/// lower bound, and the second element is the upper bound. If the upper bound is `None`
/// either there is no known upper bound, or the upper bound is larger than `usize`.
///
/// `LengthHint` implements std`::ops::{Add, Mul}` and similar traits for easy composition.
/// During computation, the lower bound will saturate at `usize::MAX`, while the upper
/// bound will become `None` if `usize::MAX` is exceeded.
#[derive(Debug, PartialEq, Eq, Copy, Clone)]
#[non_exhaustive]
pub struct LengthHint(pub usize, pub Option<usize>);
impl LengthHint {
pub fn undefined() -> Self {
Self(0, None)
}
/// `write_to` will use exactly n bytes.
pub fn exact(n: usize) -> Self {
Self(n, Some(n))
}
/// `write_to` will use at least n bytes.
pub fn at_least(n: usize) -> Self {
Self(n, None)
}
/// `write_to` will use at most n bytes.
pub fn at_most(n: usize) -> Self {
Self(0, Some(n))
}
/// `write_to` will use between `n` and `m` bytes.
pub fn between(n: usize, m: usize) -> Self {
Self(Ord::min(n, m), Some(Ord::max(n, m)))
}
/// Returns a recommendation for the number of bytes to pre-allocate.
/// If an upper bound exists, this is used, otherwise the lower bound
/// (which might be 0).
///
/// # Examples
///
/// ```
/// use writeable::Writeable;
///
/// fn pre_allocate_string(w: &impl Writeable) -> String {
/// String::with_capacity(w.writeable_length_hint().capacity())
/// }
/// ```
pub fn capacity(&self) -> usize {
self.1.unwrap_or(self.0)
}
/// Returns whether the `LengthHint` indicates that the string is exactly 0 bytes long.
pub fn is_zero(&self) -> bool {
self.1 == Some(0)
}
}
/// [`Part`]s are used as annotations for formatted strings. For example, a string like
/// `Alice, Bob` could assign a `NAME` part to the substrings `Alice` and `Bob`, and a
/// `PUNCTUATION` part to `, `. This allows for example to apply styling only to names.
///
/// `Part` contains two fields, whose usage is left up to the producer of the [`Writeable`].
/// Conventionally, the `category` field will identify the formatting logic that produces
/// the string/parts, whereas the `value` field will have semantic meaning. `NAME` and
/// `PUNCTUATION` could thus be defined as
/// ```
/// # use writeable::Part;
/// const NAME: Part = Part {
/// category: "userlist",
/// value: "name",
/// };
/// const PUNCTUATION: Part = Part {
/// category: "userlist",
/// value: "punctuation",
/// };
/// ```
///
/// That said, consumers should not usually have to inspect `Part` internals. Instead,
/// formatters should expose the `Part`s they produces as constants.
#[derive(Clone, Copy, Debug, PartialEq)]
#[allow(clippy::exhaustive_structs)] // stable
pub struct Part {
pub category: &'static str,
pub value: &'static str,
}
impl Part {
/// A part that should annotate error segments in [`TryWriteable`] output.
///
/// For an example, see [`TryWriteable`].
pub const ERROR: Part = Part {
category: "writeable",
value: "error",
};
}
/// A sink that supports annotating parts of the string with `Part`s.
pub trait PartsWrite: fmt::Write {
type SubPartsWrite: PartsWrite + ?Sized;
fn with_part(
&mut self,
part: Part,
f: impl FnMut(&mut Self::SubPartsWrite) -> fmt::Result,
) -> fmt::Result;
}
/// `Writeable` is an alternative to `std::fmt::Display` with the addition of a length function.
pub trait Writeable {
/// Writes a string to the given sink. Errors from the sink are bubbled up.
/// The default implementation delegates to `write_to_parts`, and discards any
/// `Part` annotations.
fn write_to<W: fmt::Write + ?Sized>(&self, sink: &mut W) -> fmt::Result {
self.write_to_parts(&mut parts_write_adapter::CoreWriteAsPartsWrite(sink))
}
/// Write bytes and `Part` annotations to the given sink. Errors from the
/// sink are bubbled up. The default implementation delegates to `write_to`,
/// and doesn't produce any `Part` annotations.
fn write_to_parts<S: PartsWrite + ?Sized>(&self, sink: &mut S) -> fmt::Result {
self.write_to(sink)
}
/// Returns a hint for the number of UTF-8 bytes that will be written to the sink.
///
/// Override this method if it can be computed quickly.
fn writeable_length_hint(&self) -> LengthHint {
LengthHint::undefined()
}
/// Creates a new `String` with the data from this `Writeable`. Like `ToString`,
/// but smaller and faster.
///
/// The default impl allocates an owned `String`. However, if it is possible to return a
/// borrowed string, overwrite this method to return a `Cow::Borrowed`.
///
/// To remove the `Cow` wrapper, call `.into_owned()` or `.as_str()` as appropriate.
///
/// # Examples
///
/// Inspect a `Writeable` before writing it to the sink:
///
/// ```
/// use core::fmt::{Result, Write};
/// use writeable::Writeable;
///
/// fn write_if_ascii<W, S>(w: &W, sink: &mut S) -> Result
/// where
/// W: Writeable + ?Sized,
/// S: Write + ?Sized,
/// {
/// let s = w.write_to_string();
/// if s.is_ascii() {
/// sink.write_str(&s)
/// } else {
/// Ok(())
/// }
/// }
/// ```
///
/// Convert the `Writeable` into a fully owned `String`:
///
/// ```
/// use writeable::Writeable;
///
/// fn make_string(w: &impl Writeable) -> String {
/// w.write_to_string().into_owned()
/// }
/// ```
fn write_to_string(&self) -> Cow<str> {
let hint = self.writeable_length_hint();
if hint.is_zero() {
return Cow::Borrowed("");
}
let mut output = String::with_capacity(hint.capacity());
let _ = self.write_to(&mut output);
Cow::Owned(output)
}
/// Compares the contents of this `Writeable` to the given bytes
/// without allocating a String to hold the `Writeable` contents.
///
/// This returns a lexicographical comparison, the same as if the Writeable
/// were first converted to a String and then compared with `Ord`. For a
/// locale-sensitive string ordering, use an ICU4X Collator.
///
/// # Examples
///
/// ```
/// use core::cmp::Ordering;
/// use core::fmt;
/// use writeable::Writeable;
///
/// struct WelcomeMessage<'s> {
/// pub name: &'s str,
/// }
///
/// impl<'s> Writeable for WelcomeMessage<'s> {
/// // see impl in Writeable docs
/// # fn write_to<W: fmt::Write + ?Sized>(&self, sink: &mut W) -> fmt::Result {
/// # sink.write_str("Hello, ")?;
/// # sink.write_str(self.name)?;
/// # sink.write_char('!')?;
/// # Ok(())
/// # }
/// }
///
/// let message = WelcomeMessage { name: "Alice" };
/// let message_str = message.write_to_string();
///
/// assert_eq!(Ordering::Equal, message.writeable_cmp_bytes(b"Hello, Alice!"));
///
/// assert_eq!(Ordering::Greater, message.writeable_cmp_bytes(b"Alice!"));
/// assert_eq!(Ordering::Greater, (*message_str).cmp("Alice!"));
///
/// assert_eq!(Ordering::Less, message.writeable_cmp_bytes(b"Hello, Bob!"));
/// assert_eq!(Ordering::Less, (*message_str).cmp("Hello, Bob!"));
/// ```
fn writeable_cmp_bytes(&self, other: &[u8]) -> core::cmp::Ordering {
let mut wc = cmp::WriteComparator::new(other);
let _ = self.write_to(&mut wc);
wc.finish().reverse()
}
}
/// Implements [`Display`](core::fmt::Display) for types that implement [`Writeable`].
///
/// It's recommended to do this for every [`Writeable`] type, as it will add
/// support for `core::fmt` features like [`fmt!`](std::fmt),
/// [`print!`](std::print), [`write!`](std::write), etc.
#[macro_export]
macro_rules! impl_display_with_writeable {
($type:ty) => {
/// This trait is implemented for compatibility with [`fmt!`](alloc::fmt).
/// To create a string, [`Writeable::write_to_string`] is usually more efficient.
impl core::fmt::Display for $type {
#[inline]
fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
$crate::Writeable::write_to(&self, f)
}
}
};
}
/// Testing macros for types implementing [`Writeable`].
///
/// Arguments, in order:
///
/// 1. The [`Writeable`] under test
/// 2. The expected string value
/// 3. [`*_parts_eq`] only: a list of parts (`[(start, end, Part)]`)
///
/// Any remaining arguments get passed to `format!`
///
/// The macros tests the following:
///
/// - Equality of string content
/// - Equality of parts ([`*_parts_eq`] only)
/// - Validity of size hint
/// - Reflexivity of `cmp_bytes` and order against largest and smallest strings
///
/// # Examples
///
/// ```
/// # use writeable::Writeable;
/// # use writeable::LengthHint;
/// # use writeable::Part;
/// # use writeable::assert_writeable_eq;
/// # use writeable::assert_writeable_parts_eq;
/// # use std::fmt::{self, Write};
///
/// const WORD: Part = Part {
/// category: "foo",
/// value: "word",
/// };
///
/// struct Demo;
/// impl Writeable for Demo {
/// fn write_to_parts<S: writeable::PartsWrite + ?Sized>(
/// &self,
/// sink: &mut S,
/// ) -> fmt::Result {
/// sink.with_part(WORD, |w| w.write_str("foo"))
/// }
/// fn writeable_length_hint(&self) -> LengthHint {
/// LengthHint::exact(3)
/// }
/// }
///
/// writeable::impl_display_with_writeable!(Demo);
///
/// assert_writeable_eq!(&Demo, "foo");
/// assert_writeable_eq!(&Demo, "foo", "Message: {}", "Hello World");
///
/// assert_writeable_parts_eq!(&Demo, "foo", [(0, 3, WORD)]);
/// assert_writeable_parts_eq!(
/// &Demo,
/// "foo",
/// [(0, 3, WORD)],
/// "Message: {}",
/// "Hello World"
/// );
/// ```
///
/// [`*_parts_eq`]: assert_writeable_parts_eq
#[macro_export]
macro_rules! assert_writeable_eq {
($actual_writeable:expr, $expected_str:expr $(,)?) => {
$crate::assert_writeable_eq!($actual_writeable, $expected_str, "")
};
($actual_writeable:expr, $expected_str:expr, $($arg:tt)+) => {{
$crate::assert_writeable_eq!(@internal, $actual_writeable, $expected_str, $($arg)*);
}};
(@internal, $actual_writeable:expr, $expected_str:expr, $($arg:tt)+) => {{
let actual_writeable = &$actual_writeable;
let (actual_str, actual_parts) = $crate::_internal::writeable_to_parts_for_test(actual_writeable);
let actual_len = actual_str.len();
assert_eq!(actual_str, $expected_str, $($arg)*);
assert_eq!(actual_str, $crate::Writeable::write_to_string(actual_writeable), $($arg)+);
let length_hint = $crate::Writeable::writeable_length_hint(actual_writeable);
let lower = length_hint.0;
assert!(
lower <= actual_len,
"hint lower bound {lower} larger than actual length {actual_len}: {}",
format!($($arg)*),
);
if let Some(upper) = length_hint.1 {
assert!(
actual_len <= upper,
"hint upper bound {upper} smaller than actual length {actual_len}: {}",
format!($($arg)*),
);
}
assert_eq!(actual_writeable.to_string(), $expected_str);
let ordering = $crate::Writeable::writeable_cmp_bytes(actual_writeable, $expected_str.as_bytes());
assert_eq!(ordering, core::cmp::Ordering::Equal, $($arg)*);
let ordering = $crate::Writeable::writeable_cmp_bytes(actual_writeable, "\u{10FFFF}".as_bytes());
assert_eq!(ordering, core::cmp::Ordering::Less, $($arg)*);
if $expected_str != "" {
let ordering = $crate::Writeable::writeable_cmp_bytes(actual_writeable, "".as_bytes());
assert_eq!(ordering, core::cmp::Ordering::Greater, $($arg)*);
}
actual_parts // return for assert_writeable_parts_eq
}};
}
/// See [`assert_writeable_eq`].
#[macro_export]
macro_rules! assert_writeable_parts_eq {
($actual_writeable:expr, $expected_str:expr, $expected_parts:expr $(,)?) => {
$crate::assert_writeable_parts_eq!($actual_writeable, $expected_str, $expected_parts, "")
};
($actual_writeable:expr, $expected_str:expr, $expected_parts:expr, $($arg:tt)+) => {{
let actual_parts = $crate::assert_writeable_eq!(@internal, $actual_writeable, $expected_str, $($arg)*);
assert_eq!(actual_parts, $expected_parts, $($arg)+);
}};
}