1 files changed, 107 insertions, 0 deletions
diff --git a/third_party/rust/litrs/src/byte/mod.rs b/third_party/rust/litrs/src/byte/mod.rs
new file mode 100644
index 0000000000..ffdff5d04a
--- /dev/null
+++ b/third_party/rust/litrs/src/byte/mod.rs
@@ -0,0 +1,107 @@
+use core::fmt;
+
+use crate::{
+    Buffer, ParseError,
+    err::{perr, ParseErrorKind::*},
+    escape::unescape,
+    parse::check_suffix,
+};
+
+
+/// A (single) byte literal, e.g. `b'k'` or `b'!'`.
+///
+/// See [the reference][ref] for more information.
+///
+/// [ref]: https://doc.rust-lang.org/reference/tokens.html#byte-literals
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct ByteLit<B: Buffer> {
+    raw: B,
+    /// Start index of the suffix or `raw.len()` if there is no suffix.
+    start_suffix: usize,
+    value: u8,
+}
+
+impl<B: Buffer> ByteLit<B> {
+    /// Parses the input as a byte literal. Returns an error if the input is
+    /// invalid or represents a different kind of literal.
+    pub fn parse(input: B) -> Result<Self, ParseError> {
+        if input.is_empty() {
+            return Err(perr(None, Empty));
+        }
+        if !input.starts_with("b'") {
+            return Err(perr(None, InvalidByteLiteralStart));
+        }
+
+        let (value, start_suffix) = parse_impl(&input)?;
+        Ok(Self { raw: input, value, start_suffix })
+    }
+
+    /// Returns the byte value that this literal represents.
+    pub fn value(&self) -> u8 {
+        self.value
+    }
+
+    /// The optional suffix. Returns `""` if the suffix is empty/does not exist.
+    pub fn suffix(&self) -> &str {
+        &(*self.raw)[self.start_suffix..]
+    }
+
+    /// Returns the raw input that was passed to `parse`.
+    pub fn raw_input(&self) -> &str {
+        &self.raw
+    }
+
+    /// Returns the raw input that was passed to `parse`, potentially owned.
+    pub fn into_raw_input(self) -> B {
+        self.raw
+    }
+
+}
+
+impl ByteLit<&str> {
+    /// Makes a copy of the underlying buffer and returns the owned version of
+    /// `Self`.
+    pub fn to_owned(&self) -> ByteLit<String> {
+        ByteLit {
+            raw: self.raw.to_owned(),
+            start_suffix: self.start_suffix,
+            value: self.value,
+        }
+    }
+}
+
+impl<B: Buffer> fmt::Display for ByteLit<B> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad(&self.raw)
+    }
+}
+
+/// Precondition: must start with `b'`.
+#[inline(never)]
+pub(crate) fn parse_impl(input: &str) -> Result<(u8, usize), ParseError> {
+    let input_bytes = input.as_bytes();
+    let first = input_bytes.get(2).ok_or(perr(None, UnterminatedByteLiteral))?;
+    let (c, len) = match first {
+        b'\'' if input_bytes.get(3) == Some(&b'\'') => return Err(perr(2, UnescapedSingleQuote)),
+        b'\'' => return Err(perr(None, EmptyByteLiteral)),
+        b'\n' | b'\t' | b'\r' => return Err(perr(2, UnescapedSpecialWhitespace)),
+        b'\\' => unescape::<u8>(&input[2..], 2)?,
+        other if other.is_ascii() => (*other, 1),
+        _ => return Err(perr(2, NonAsciiInByteLiteral)),
+    };
+
+    match input[2 + len..].find('\'') {
+        Some(0) => {}
+        Some(_) => return Err(perr(None, OverlongByteLiteral)),
+        None => return Err(perr(None, UnterminatedByteLiteral)),
+    }
+
+    let start_suffix = 2 + len + 1;
+    let suffix = &input[start_suffix..];
+    check_suffix(suffix).map_err(|kind| perr(start_suffix, kind))?;
+
+    Ok((c, start_suffix))
+}
+
+#[cfg(test)]
+mod tests;