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//! Defines utf8 error type.

use crate::fmt;

/// Errors which can occur when attempting to interpret a sequence of [`u8`]
/// as a string.
///
/// As such, the `from_utf8` family of functions and methods for both [`String`]s
/// and [`&str`]s make use of this error, for example.
///
/// [`String`]: ../../std/string/struct.String.html#method.from_utf8
/// [`&str`]: super::from_utf8
///
/// # Examples
///
/// This error type’s methods can be used to create functionality
/// similar to `String::from_utf8_lossy` without allocating heap memory:
///
/// ```
/// fn from_utf8_lossy<F>(mut input: &[u8], mut push: F) where F: FnMut(&str) {
///     loop {
///         match std::str::from_utf8(input) {
///             Ok(valid) => {
///                 push(valid);
///                 break
///             }
///             Err(error) => {
///                 let (valid, after_valid) = input.split_at(error.valid_up_to());
///                 unsafe {
///                     push(std::str::from_utf8_unchecked(valid))
///                 }
///                 push("\u{FFFD}");
///
///                 if let Some(invalid_sequence_length) = error.error_len() {
///                     input = &after_valid[invalid_sequence_length..]
///                 } else {
///                     break
///                 }
///             }
///         }
///     }
/// }
/// ```
#[derive(Copy, Eq, PartialEq, Clone, Debug)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Utf8Error {
    pub(super) valid_up_to: usize,
    pub(super) error_len: Option<u8>,
}

impl Utf8Error {
    /// Returns the index in the given string up to which valid UTF-8 was
    /// verified.
    ///
    /// It is the maximum index such that `from_utf8(&input[..index])`
    /// would return `Ok(_)`.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use std::str;
    ///
    /// // some invalid bytes, in a vector
    /// let sparkle_heart = vec![0, 159, 146, 150];
    ///
    /// // std::str::from_utf8 returns a Utf8Error
    /// let error = str::from_utf8(&sparkle_heart).unwrap_err();
    ///
    /// // the second byte is invalid here
    /// assert_eq!(1, error.valid_up_to());
    /// ```
    #[stable(feature = "utf8_error", since = "1.5.0")]
    #[rustc_const_unstable(feature = "const_str_from_utf8", issue = "91006")]
    #[must_use]
    #[inline]
    pub const fn valid_up_to(&self) -> usize {
        self.valid_up_to
    }

    /// Provides more information about the failure:
    ///
    /// * `None`: the end of the input was reached unexpectedly.
    ///   `self.valid_up_to()` is 1 to 3 bytes from the end of the input.
    ///   If a byte stream (such as a file or a network socket) is being decoded incrementally,
    ///   this could be a valid `char` whose UTF-8 byte sequence is spanning multiple chunks.
    ///
    /// * `Some(len)`: an unexpected byte was encountered.
    ///   The length provided is that of the invalid byte sequence
    ///   that starts at the index given by `valid_up_to()`.
    ///   Decoding should resume after that sequence
    ///   (after inserting a [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD]) in case of
    ///   lossy decoding.
    ///
    /// [U+FFFD]: ../../std/char/constant.REPLACEMENT_CHARACTER.html
    #[stable(feature = "utf8_error_error_len", since = "1.20.0")]
    #[rustc_const_unstable(feature = "const_str_from_utf8", issue = "91006")]
    #[must_use]
    #[inline]
    pub const fn error_len(&self) -> Option<usize> {
        // This should become `map` again, once it's `const`
        match self.error_len {
            Some(len) => Some(len as usize),
            None => None,
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for Utf8Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if let Some(error_len) = self.error_len {
            write!(
                f,
                "invalid utf-8 sequence of {} bytes from index {}",
                error_len, self.valid_up_to
            )
        } else {
            write!(f, "incomplete utf-8 byte sequence from index {}", self.valid_up_to)
        }
    }
}

/// An error returned when parsing a `bool` using [`from_str`] fails
///
/// [`from_str`]: super::FromStr::from_str
#[derive(Debug, Clone, PartialEq, Eq)]
#[non_exhaustive]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct ParseBoolError;

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for ParseBoolError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        "provided string was not `true` or `false`".fmt(f)
    }
}