235 lines
8.3 KiB
Rust
235 lines
8.3 KiB
Rust
// Copyright Mozilla Foundation
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//
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// Licensed under the Apache License (Version 2.0), or the MIT license,
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// (the "Licenses") at your option. You may not use this file except in
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// compliance with one of the Licenses. You may obtain copies of the
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// Licenses at:
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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// https://opensource.org/licenses/MIT
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the Licenses is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the Licenses for the specific language governing permissions and
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// limitations under the Licenses.
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use crate::in_inclusive_range8;
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use crate::UTF8_DATA;
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use core::fmt::Formatter;
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use core::iter::FusedIterator;
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/// A type for signaling UTF-8 errors.
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///
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/// Note: `core::error::Error` is not implemented due to implementing it
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/// being an [unstable feature][1] at the time of writing.
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///
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/// [1]: https://github.com/rust-lang/rust/issues/103765
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#[derive(Debug, PartialEq)]
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#[non_exhaustive]
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pub struct Utf8CharsError;
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impl core::fmt::Display for Utf8CharsError {
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fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), core::fmt::Error> {
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write!(f, "byte sequence not well-formed UTF-8")
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}
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}
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/// Iterator by `Result<char,Utf8CharsError>` over `&[u8]` that contains
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/// potentially-invalid UTF-8. There is exactly one `Utf8CharsError` per
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/// each error as defined by the WHATWG Encoding Standard.
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///
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/// ```
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/// let s = b"a\xFFb\xFF\x80c\xF0\x9F\xA4\xA6\xF0\x9F\xA4\xF0\x9F\xF0d";
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/// let plain = utf8_iter::Utf8Chars::new(s);
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/// let reporting = utf8_iter::ErrorReportingUtf8Chars::new(s);
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/// assert!(plain.eq(reporting.map(|r| r.unwrap_or('\u{FFFD}'))));
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/// ```
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#[derive(Debug, Clone)]
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pub struct ErrorReportingUtf8Chars<'a> {
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remaining: &'a [u8],
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}
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impl<'a> ErrorReportingUtf8Chars<'a> {
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#[inline(always)]
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/// Creates the iterator from a byte slice.
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pub fn new(bytes: &'a [u8]) -> Self {
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ErrorReportingUtf8Chars::<'a> { remaining: bytes }
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}
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/// Views the current remaining data in the iterator as a subslice
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/// of the original slice.
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#[inline(always)]
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pub fn as_slice(&self) -> &'a [u8] {
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self.remaining
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}
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#[inline(never)]
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fn next_fallback(&mut self) -> Option<Result<char, Utf8CharsError>> {
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if self.remaining.is_empty() {
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return None;
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}
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let first = self.remaining[0];
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if first < 0x80 {
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self.remaining = &self.remaining[1..];
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return Some(Ok(char::from(first)));
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}
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if !in_inclusive_range8(first, 0xC2, 0xF4) || self.remaining.len() == 1 {
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self.remaining = &self.remaining[1..];
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return Some(Err(Utf8CharsError));
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}
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let second = self.remaining[1];
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let (lower_bound, upper_bound) = match first {
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0xE0 => (0xA0, 0xBF),
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0xED => (0x80, 0x9F),
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0xF0 => (0x90, 0xBF),
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0xF4 => (0x80, 0x8F),
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_ => (0x80, 0xBF),
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};
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if !in_inclusive_range8(second, lower_bound, upper_bound) {
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self.remaining = &self.remaining[1..];
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return Some(Err(Utf8CharsError));
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}
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if first < 0xE0 {
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self.remaining = &self.remaining[2..];
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let point = ((u32::from(first) & 0x1F) << 6) | (u32::from(second) & 0x3F);
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return Some(Ok(unsafe { char::from_u32_unchecked(point) }));
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}
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if self.remaining.len() == 2 {
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self.remaining = &self.remaining[2..];
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return Some(Err(Utf8CharsError));
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}
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let third = self.remaining[2];
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if !in_inclusive_range8(third, 0x80, 0xBF) {
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self.remaining = &self.remaining[2..];
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return Some(Err(Utf8CharsError));
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}
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if first < 0xF0 {
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self.remaining = &self.remaining[3..];
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let point = ((u32::from(first) & 0xF) << 12)
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| ((u32::from(second) & 0x3F) << 6)
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| (u32::from(third) & 0x3F);
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return Some(Ok(unsafe { char::from_u32_unchecked(point) }));
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}
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// At this point, we have a valid 3-byte prefix of a
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// four-byte sequence that has to be incomplete, because
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// otherwise `next()` would have succeeded.
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self.remaining = &self.remaining[3..];
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Some(Err(Utf8CharsError))
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}
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}
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impl<'a> Iterator for ErrorReportingUtf8Chars<'a> {
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type Item = Result<char, Utf8CharsError>;
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#[inline]
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fn next(&mut self) -> Option<Result<char, Utf8CharsError>> {
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// This loop is only broken out of as goto forward
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#[allow(clippy::never_loop)]
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loop {
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if self.remaining.len() < 4 {
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break;
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}
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let first = self.remaining[0];
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if first < 0x80 {
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self.remaining = &self.remaining[1..];
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return Some(Ok(char::from(first)));
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}
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let second = self.remaining[1];
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if in_inclusive_range8(first, 0xC2, 0xDF) {
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if !in_inclusive_range8(second, 0x80, 0xBF) {
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break;
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}
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let point = ((u32::from(first) & 0x1F) << 6) | (u32::from(second) & 0x3F);
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self.remaining = &self.remaining[2..];
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return Some(Ok(unsafe { char::from_u32_unchecked(point) }));
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}
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// This table-based formulation was benchmark-based in encoding_rs,
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// but it hasn't been re-benchmarked in this iterator context.
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let third = self.remaining[2];
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if first < 0xF0 {
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if ((UTF8_DATA.table[usize::from(second)]
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& UTF8_DATA.table[usize::from(first) + 0x80])
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| (third >> 6))
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!= 2
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{
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break;
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}
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let point = ((u32::from(first) & 0xF) << 12)
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| ((u32::from(second) & 0x3F) << 6)
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| (u32::from(third) & 0x3F);
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self.remaining = &self.remaining[3..];
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return Some(Ok(unsafe { char::from_u32_unchecked(point) }));
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}
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let fourth = self.remaining[3];
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if (u16::from(
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UTF8_DATA.table[usize::from(second)] & UTF8_DATA.table[usize::from(first) + 0x80],
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) | u16::from(third >> 6)
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| (u16::from(fourth & 0xC0) << 2))
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!= 0x202
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{
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break;
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}
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let point = ((u32::from(first) & 0x7) << 18)
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| ((u32::from(second) & 0x3F) << 12)
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| ((u32::from(third) & 0x3F) << 6)
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| (u32::from(fourth) & 0x3F);
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self.remaining = &self.remaining[4..];
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return Some(Ok(unsafe { char::from_u32_unchecked(point) }));
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}
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self.next_fallback()
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}
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}
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impl<'a> DoubleEndedIterator for ErrorReportingUtf8Chars<'a> {
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#[inline]
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fn next_back(&mut self) -> Option<Result<char, Utf8CharsError>> {
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if self.remaining.is_empty() {
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return None;
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}
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let mut attempt = 1;
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for b in self.remaining.iter().rev() {
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if b & 0xC0 != 0x80 {
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let (head, tail) = self.remaining.split_at(self.remaining.len() - attempt);
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let mut inner = ErrorReportingUtf8Chars::new(tail);
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let candidate = inner.next();
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if inner.as_slice().is_empty() {
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self.remaining = head;
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return candidate;
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}
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break;
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}
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if attempt == 4 {
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break;
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}
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attempt += 1;
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}
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self.remaining = &self.remaining[..self.remaining.len() - 1];
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Some(Err(Utf8CharsError))
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}
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}
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impl FusedIterator for ErrorReportingUtf8Chars<'_> {}
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#[cfg(test)]
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mod tests {
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use crate::ErrorReportingUtf8Chars;
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// Should be a static assert, but not taking a dependency for this.
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#[test]
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fn test_size() {
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assert_eq!(
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core::mem::size_of::<Option<<ErrorReportingUtf8Chars<'_> as Iterator>::Item>>(),
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core::mem::size_of::<Option<char>>()
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);
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}
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#[test]
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fn test_eq() {
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let a: <ErrorReportingUtf8Chars<'_> as Iterator>::Item = Ok('a');
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let a_again: <ErrorReportingUtf8Chars<'_> as Iterator>::Item = Ok('a');
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assert_eq!(a, a_again);
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}
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}
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