Source code
Revision control
Copy as Markdown
Other Tools
// 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
use super::*;
use crate::parts_write_adapter::CoreWriteAsPartsWrite;
use core::{cmp::Ordering, convert::Infallible};
/// A writeable object that can fail while writing.
///
/// The default [`Writeable`] trait returns a [`fmt::Error`], which originates from the sink.
/// In contrast, this trait allows the _writeable itself_ to trigger an error as well.
///
/// Implementations are expected to always make a _best attempt_ at writing to the sink
/// and should write replacement values in the error state. Therefore, the returned `Result`
/// can be safely ignored to emulate a "lossy" mode.
///
/// Any error substrings should be annotated with [`Part::ERROR`].
///
/// # Implementer Notes
///
/// This trait requires that implementers make a _best attempt_ at writing to the sink,
/// _even in the error state_, such as with a placeholder or fallback string.
///
/// In [`TryWriteable::try_write_to_parts()`], error substrings should be annotated with
/// [`Part::ERROR`]. Because of this, writing to parts is not default-implemented like
/// it is on [`Writeable`].
///
/// The trait is implemented on [`Result<T, E>`] where `T` and `E` both implement [`Writeable`];
/// In the `Ok` case, `T` is written, and in the `Err` case, `E` is written as a fallback value.
/// This impl, which writes [`Part::ERROR`], can be used as a basis for more advanced impls.
///
/// # Examples
///
/// Implementing on a custom type:
///
/// ```
/// use core::fmt;
/// use writeable::LengthHint;
/// use writeable::PartsWrite;
/// use writeable::TryWriteable;
///
/// #[derive(Debug, PartialEq, Eq)]
/// enum HelloWorldWriteableError {
/// MissingName,
/// }
///
/// #[derive(Debug, PartialEq, Eq)]
/// struct HelloWorldWriteable {
/// pub name: Option<&'static str>,
/// }
///
/// impl TryWriteable for HelloWorldWriteable {
/// type Error = HelloWorldWriteableError;
///
/// fn try_write_to_parts<S: PartsWrite + ?Sized>(
/// &self,
/// sink: &mut S,
/// ) -> Result<Result<(), Self::Error>, fmt::Error> {
/// sink.write_str("Hello, ")?;
/// // Use `impl TryWriteable for Result` to generate the error part:
/// let err = self.name.ok_or("nobody").try_write_to_parts(sink)?.err();
/// sink.write_char('!')?;
/// // Return a doubly-wrapped Result.
/// // The outer Result is for fmt::Error, handled by the `?`s above.
/// // The inner Result is for our own Self::Error.
/// if err.is_none() {
/// Ok(Ok(()))
/// } else {
/// Ok(Err(HelloWorldWriteableError::MissingName))
/// }
/// }
///
/// fn writeable_length_hint(&self) -> LengthHint {
/// self.name.ok_or("nobody").writeable_length_hint() + 8
/// }
/// }
///
/// // Success case:
/// writeable::assert_try_writeable_eq!(
/// HelloWorldWriteable {
/// name: Some("Alice")
/// },
/// "Hello, Alice!"
/// );
///
/// // Failure case, including the ERROR part:
/// writeable::assert_try_writeable_parts_eq!(
/// HelloWorldWriteable { name: None },
/// "Hello, nobody!",
/// Err(HelloWorldWriteableError::MissingName),
/// [(7, 13, writeable::Part::ERROR)]
/// );
/// ```
pub trait TryWriteable {
type Error;
/// Writes the content of this writeable to a sink.
///
/// If the sink hits an error, writing immediately ends,
/// `Err(`[`fmt::Error`]`)` is returned, and the sink does not contain valid output.
///
/// If the writeable hits an error, writing is continued with a replacement value,
/// `Ok(Err(`[`TryWriteable::Error`]`))` is returned, and the caller may continue using the sink.
///
/// # Lossy Mode
///
/// The [`fmt::Error`] should always be handled, but the [`TryWriteable::Error`] can be
/// ignored if a fallback string is desired instead of an error.
///
/// To handle the sink error, but not the writeable error, write:
///
/// ```
/// # use writeable::TryWriteable;
/// # let my_writeable: Result<&str, &str> = Ok("");
/// # let mut sink = String::new();
/// let _ = my_writeable.try_write_to(&mut sink)?;
/// # Ok::<(), core::fmt::Error>(())
/// ```
///
/// # Examples
///
/// The following examples use `Result<&str, usize>`, which implements [`TryWriteable`] because both `&str` and `usize` do.
///
/// Success case:
///
/// ```
/// use writeable::TryWriteable;
///
/// let w: Result<&str, usize> = Ok("success");
/// let mut sink = String::new();
/// let result = w.try_write_to(&mut sink);
///
/// assert_eq!(result, Ok(Ok(())));
/// assert_eq!(sink, "success");
/// ```
///
/// Failure case:
///
/// ```
/// use writeable::TryWriteable;
///
/// let w: Result<&str, usize> = Err(44);
/// let mut sink = String::new();
/// let result = w.try_write_to(&mut sink);
///
/// assert_eq!(result, Ok(Err(44)));
/// assert_eq!(sink, "44");
/// ```
fn try_write_to<W: fmt::Write + ?Sized>(
&self,
sink: &mut W,
) -> Result<Result<(), Self::Error>, fmt::Error> {
self.try_write_to_parts(&mut CoreWriteAsPartsWrite(sink))
}
/// Writes the content of this writeable to a sink with parts (annotations).
///
/// For more information, see:
///
/// - [`TryWriteable::try_write_to()`] for the general behavior.
/// - [`TryWriteable`] for an example with parts.
/// - [`Part`] for more about parts.
fn try_write_to_parts<S: PartsWrite + ?Sized>(
&self,
sink: &mut S,
) -> Result<Result<(), Self::Error>, fmt::Error>;
/// Returns a hint for the number of UTF-8 bytes that will be written to the sink.
///
/// This function returns the length of the "lossy mode" string; for more information,
/// see [`TryWriteable::try_write_to()`].
fn writeable_length_hint(&self) -> LengthHint {
LengthHint::undefined()
}
/// Writes the content of this writeable to a string.
///
/// In the failure case, this function returns the error and the best-effort string ("lossy mode").
///
/// Examples
///
/// ```
/// # use std::borrow::Cow;
/// # use writeable::TryWriteable;
/// // use the best-effort string
/// let r1: Cow<str> = Ok::<&str, u8>("ok")
/// .try_write_to_string()
/// .unwrap_or_else(|(_, s)| s);
/// // propagate the error
/// let r2: Result<Cow<str>, u8> = Ok::<&str, u8>("ok")
/// .try_write_to_string()
/// .map_err(|(e, _)| e);
/// ```
fn try_write_to_string(&self) -> Result<Cow<str>, (Self::Error, Cow<str>)> {
let hint = self.writeable_length_hint();
if hint.is_zero() {
return Ok(Cow::Borrowed(""));
}
let mut output = String::with_capacity(hint.capacity());
match self
.try_write_to(&mut output)
.unwrap_or_else(|fmt::Error| Ok(()))
{
Ok(()) => Ok(Cow::Owned(output)),
Err(e) => Err((e, Cow::Owned(output))),
}
}
/// Compares the content of this writeable to a byte slice.
///
/// This function compares the "lossy mode" string; for more information,
/// see [`TryWriteable::try_write_to()`].
///
/// For more information, see [`Writeable::writeable_cmp_bytes()`].
///
/// # Examples
///
/// ```
/// use core::cmp::Ordering;
/// use core::fmt;
/// use writeable::TryWriteable;
/// # use writeable::PartsWrite;
/// # use writeable::LengthHint;
///
/// #[derive(Debug, PartialEq, Eq)]
/// enum HelloWorldWriteableError {
/// MissingName
/// }
///
/// #[derive(Debug, PartialEq, Eq)]
/// struct HelloWorldWriteable {
/// pub name: Option<&'static str>
/// }
///
/// impl TryWriteable for HelloWorldWriteable {
/// type Error = HelloWorldWriteableError;
/// // see impl in TryWriteable docs
/// # fn try_write_to_parts<S: PartsWrite + ?Sized>(
/// # &self,
/// # sink: &mut S,
/// # ) -> Result<Result<(), Self::Error>, fmt::Error> {
/// # sink.write_str("Hello, ")?;
/// # // Use `impl TryWriteable for Result` to generate the error part:
/// # let _ = self.name.ok_or("nobody").try_write_to_parts(sink)?;
/// # sink.write_char('!')?;
/// # // Return a doubly-wrapped Result.
/// # // The outer Result is for fmt::Error, handled by the `?`s above.
/// # // The inner Result is for our own Self::Error.
/// # if self.name.is_some() {
/// # Ok(Ok(()))
/// # } else {
/// # Ok(Err(HelloWorldWriteableError::MissingName))
/// # }
/// # }
/// }
///
/// // Success case:
/// let writeable = HelloWorldWriteable { name: Some("Alice") };
/// let writeable_str = writeable.try_write_to_string().expect("name is Some");
///
/// assert_eq!(Ordering::Equal, writeable.writeable_cmp_bytes(b"Hello, Alice!"));
///
/// assert_eq!(Ordering::Greater, writeable.writeable_cmp_bytes(b"Alice!"));
/// assert_eq!(Ordering::Greater, (*writeable_str).cmp("Alice!"));
///
/// assert_eq!(Ordering::Less, writeable.writeable_cmp_bytes(b"Hello, Bob!"));
/// assert_eq!(Ordering::Less, (*writeable_str).cmp("Hello, Bob!"));
///
/// // Failure case:
/// let writeable = HelloWorldWriteable { name: None };
/// let mut writeable_str = String::new();
/// let _ = writeable.try_write_to(&mut writeable_str).expect("write to String is infallible");
///
/// assert_eq!(Ordering::Equal, writeable.writeable_cmp_bytes(b"Hello, nobody!"));
///
/// assert_eq!(Ordering::Greater, writeable.writeable_cmp_bytes(b"Hello, alice!"));
/// assert_eq!(Ordering::Greater, (*writeable_str).cmp("Hello, alice!"));
///
/// assert_eq!(Ordering::Less, writeable.writeable_cmp_bytes(b"Hello, zero!"));
/// assert_eq!(Ordering::Less, (*writeable_str).cmp("Hello, zero!"));
/// ```
fn writeable_cmp_bytes(&self, other: &[u8]) -> Ordering {
let mut wc = cmp::WriteComparator::new(other);
let _ = self
.try_write_to(&mut wc)
.unwrap_or_else(|fmt::Error| Ok(()));
wc.finish().reverse()
}
}
impl<T, E> TryWriteable for Result<T, E>
where
T: Writeable,
E: Writeable + Clone,
{
type Error = E;
#[inline]
fn try_write_to<W: fmt::Write + ?Sized>(
&self,
sink: &mut W,
) -> Result<Result<(), Self::Error>, fmt::Error> {
match self {
Ok(t) => t.write_to(sink).map(Ok),
Err(e) => e.write_to(sink).map(|()| Err(e.clone())),
}
}
#[inline]
fn try_write_to_parts<S: PartsWrite + ?Sized>(
&self,
sink: &mut S,
) -> Result<Result<(), Self::Error>, fmt::Error> {
match self {
Ok(t) => t.write_to_parts(sink).map(Ok),
Err(e) => sink
.with_part(Part::ERROR, |sink| e.write_to_parts(sink))
.map(|()| Err(e.clone())),
}
}
#[inline]
fn writeable_length_hint(&self) -> LengthHint {
match self {
Ok(t) => t.writeable_length_hint(),
Err(e) => e.writeable_length_hint(),
}
}
#[inline]
fn try_write_to_string(&self) -> Result<Cow<str>, (Self::Error, Cow<str>)> {
match self {
Ok(t) => Ok(t.write_to_string()),
Err(e) => Err((e.clone(), e.write_to_string())),
}
}
#[inline]
fn writeable_cmp_bytes(&self, other: &[u8]) -> Ordering {
match self {
Ok(t) => t.writeable_cmp_bytes(other),
Err(e) => e.writeable_cmp_bytes(other),
}
}
}
/// A wrapper around [`TryWriteable`] that implements [`Writeable`]
/// if [`TryWriteable::Error`] is [`Infallible`].
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
#[allow(clippy::exhaustive_structs)] // transparent newtype
pub struct TryWriteableInfallibleAsWriteable<T>(pub T);
impl<T> Writeable for TryWriteableInfallibleAsWriteable<T>
where
T: TryWriteable<Error = Infallible>,
{
#[inline]
fn write_to<W: fmt::Write + ?Sized>(&self, sink: &mut W) -> fmt::Result {
match self.0.try_write_to(sink) {
Ok(Ok(())) => Ok(()),
Ok(Err(infallible)) => match infallible {},
Err(e) => Err(e),
}
}
#[inline]
fn write_to_parts<S: PartsWrite + ?Sized>(&self, sink: &mut S) -> fmt::Result {
match self.0.try_write_to_parts(sink) {
Ok(Ok(())) => Ok(()),
Ok(Err(infallible)) => match infallible {},
Err(e) => Err(e),
}
}
#[inline]
fn writeable_length_hint(&self) -> LengthHint {
self.0.writeable_length_hint()
}
#[inline]
fn write_to_string(&self) -> Cow<str> {
match self.0.try_write_to_string() {
Ok(s) => s,
Err((infallible, _)) => match infallible {},
}
}
#[inline]
fn writeable_cmp_bytes(&self, other: &[u8]) -> core::cmp::Ordering {
self.0.writeable_cmp_bytes(other)
}
}
impl<T> fmt::Display for TryWriteableInfallibleAsWriteable<T>
where
T: TryWriteable<Error = Infallible>,
{
#[inline]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.write_to(f)
}
}
/// A wrapper around [`Writeable`] that implements [`TryWriteable`]
/// with [`TryWriteable::Error`] set to [`Infallible`].
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
#[allow(clippy::exhaustive_structs)] // transparent newtype
pub struct WriteableAsTryWriteableInfallible<T>(pub T);
impl<T> TryWriteable for WriteableAsTryWriteableInfallible<T>
where
T: Writeable,
{
type Error = Infallible;
#[inline]
fn try_write_to<W: fmt::Write + ?Sized>(
&self,
sink: &mut W,
) -> Result<Result<(), Infallible>, fmt::Error> {
self.0.write_to(sink).map(Ok)
}
#[inline]
fn try_write_to_parts<S: PartsWrite + ?Sized>(
&self,
sink: &mut S,
) -> Result<Result<(), Infallible>, fmt::Error> {
self.0.write_to_parts(sink).map(Ok)
}
#[inline]
fn writeable_length_hint(&self) -> LengthHint {
self.0.writeable_length_hint()
}
#[inline]
fn try_write_to_string(&self) -> Result<Cow<str>, (Infallible, Cow<str>)> {
Ok(self.0.write_to_string())
}
#[inline]
fn writeable_cmp_bytes(&self, other: &[u8]) -> core::cmp::Ordering {
self.0.writeable_cmp_bytes(other)
}
}
/// Testing macros for types implementing [`TryWriteable`].
///
/// Arguments, in order:
///
/// 1. The [`TryWriteable`] under test
/// 2. The expected string value
/// 3. The expected result value, or `Ok(())` if omitted
/// 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
///
/// For a usage example, see [`TryWriteable`].
///
/// [`*_parts_eq`]: assert_try_writeable_parts_eq
#[macro_export]
macro_rules! assert_try_writeable_eq {
($actual_writeable:expr, $expected_str:expr $(,)?) => {
$crate::assert_try_writeable_eq!($actual_writeable, $expected_str, Ok(()))
};
($actual_writeable:expr, $expected_str:expr, $expected_result:expr $(,)?) => {
$crate::assert_try_writeable_eq!($actual_writeable, $expected_str, $expected_result, "")
};
($actual_writeable:expr, $expected_str:expr, $expected_result:expr, $($arg:tt)+) => {{
$crate::assert_try_writeable_eq!(@internal, $actual_writeable, $expected_str, $expected_result, $($arg)*);
}};
(@internal, $actual_writeable:expr, $expected_str:expr, $expected_result:expr, $($arg:tt)+) => {{
use $crate::TryWriteable;
let actual_writeable = &$actual_writeable;
let (actual_str, actual_parts, actual_error) = $crate::_internal::try_writeable_to_parts_for_test(actual_writeable);
assert_eq!(actual_str, $expected_str, $($arg)*);
assert_eq!(actual_error, Result::<(), _>::from($expected_result).err(), $($arg)*);
let actual_result = match actual_writeable.try_write_to_string() {
Ok(actual_cow_str) => {
assert_eq!(actual_cow_str, $expected_str, $($arg)+);
Ok(())
}
Err((e, actual_cow_str)) => {
assert_eq!(actual_cow_str, $expected_str, $($arg)+);
Err(e)
}
};
assert_eq!(actual_result, Result::<(), _>::from($expected_result), $($arg)*);
let length_hint = actual_writeable.writeable_length_hint();
assert!(
length_hint.0 <= actual_str.len(),
"hint lower bound {} larger than actual length {}: {}",
length_hint.0, actual_str.len(), format!($($arg)*),
);
if let Some(upper) = length_hint.1 {
assert!(
actual_str.len() <= upper,
"hint upper bound {} smaller than actual length {}: {}",
length_hint.0, actual_str.len(), format!($($arg)*),
);
}
let ordering = actual_writeable.writeable_cmp_bytes($expected_str.as_bytes());
assert_eq!(ordering, core::cmp::Ordering::Equal, $($arg)*);
let ordering = actual_writeable.writeable_cmp_bytes("\u{10FFFF}".as_bytes());
assert_eq!(ordering, core::cmp::Ordering::Less, $($arg)*);
if $expected_str != "" {
let ordering = actual_writeable.writeable_cmp_bytes("".as_bytes());
assert_eq!(ordering, core::cmp::Ordering::Greater, $($arg)*);
}
actual_parts // return for assert_try_writeable_parts_eq
}};
}
/// See [`assert_try_writeable_eq`].
#[macro_export]
macro_rules! assert_try_writeable_parts_eq {
($actual_writeable:expr, $expected_str:expr, $expected_parts:expr $(,)?) => {
$crate::assert_try_writeable_parts_eq!($actual_writeable, $expected_str, Ok(()), $expected_parts)
};
($actual_writeable:expr, $expected_str:expr, $expected_result:expr, $expected_parts:expr $(,)?) => {
$crate::assert_try_writeable_parts_eq!($actual_writeable, $expected_str, $expected_result, $expected_parts, "")
};
($actual_writeable:expr, $expected_str:expr, $expected_result:expr, $expected_parts:expr, $($arg:tt)+) => {{
let actual_parts = $crate::assert_try_writeable_eq!(@internal, $actual_writeable, $expected_str, $expected_result, $($arg)*);
assert_eq!(actual_parts, $expected_parts, $($arg)+);
}};
}
#[test]
fn test_result_try_writeable() {
let mut result: Result<&str, usize> = Ok("success");
assert_try_writeable_eq!(result, "success");
result = Err(44);
assert_try_writeable_eq!(result, "44", Err(44));
assert_try_writeable_parts_eq!(result, "44", Err(44), [(0, 2, Part::ERROR)])
}