Revert "Rollup merge of #136355 - GuillaumeGomez:proc-macro_add_value_retrieval_methods, r=Amanieu"

This reverts commit 08dfbf49e30d917c89e49eb14cb3f1e8b8a1c9ef, reversing
changes made to 10bcdad7df0de3cfb95c7bdb7b16908e73cafc09.

3 files changed, 725 insertions, 3 deletions

diff --git a/compiler/rustc_lexer/src/lib.rs b/compiler/rustc_lexer/src/lib.rs
index c45dd33982b..61638e45253 100644
--- a/compiler/rustc_lexer/src/lib.rs
+++ b/compiler/rustc_lexer/src/lib.rs
@@ -26,13 +26,11 @@
 // tidy-alphabetical-end
 
 mod cursor;
+pub mod unescape;
 
 #[cfg(test)]
 mod tests;
 
-// FIXME: This is needed for rust-analyzer. Remove this dependency once rust-analyzer uses
-// `literal-escaper`.
-pub use literal_escaper as unescape;
 use unicode_properties::UnicodeEmoji;
 pub use unicode_xid::UNICODE_VERSION as UNICODE_XID_VERSION;
 
diff --git a/compiler/rustc_lexer/src/unescape.rs b/compiler/rustc_lexer/src/unescape.rs
new file mode 100644
index 00000000000..d6ea4249247
--- /dev/null
+++ b/compiler/rustc_lexer/src/unescape.rs
@@ -0,0 +1,438 @@
+//! Utilities for validating string and char literals and turning them into
+//! values they represent.
+
+use std::ops::Range;
+use std::str::Chars;
+
+use Mode::*;
+
+#[cfg(test)]
+mod tests;
+
+/// Errors and warnings that can occur during string unescaping. They mostly
+/// relate to malformed escape sequences, but there are a few that are about
+/// other problems.
+#[derive(Debug, PartialEq, Eq)]
+pub enum EscapeError {
+    /// Expected 1 char, but 0 were found.
+    ZeroChars,
+    /// Expected 1 char, but more than 1 were found.
+    MoreThanOneChar,
+
+    /// Escaped '\' character without continuation.
+    LoneSlash,
+    /// Invalid escape character (e.g. '\z').
+    InvalidEscape,
+    /// Raw '\r' encountered.
+    BareCarriageReturn,
+    /// Raw '\r' encountered in raw string.
+    BareCarriageReturnInRawString,
+    /// Unescaped character that was expected to be escaped (e.g. raw '\t').
+    EscapeOnlyChar,
+
+    /// Numeric character escape is too short (e.g. '\x1').
+    TooShortHexEscape,
+    /// Invalid character in numeric escape (e.g. '\xz')
+    InvalidCharInHexEscape,
+    /// Character code in numeric escape is non-ascii (e.g. '\xFF').
+    OutOfRangeHexEscape,
+
+    /// '\u' not followed by '{'.
+    NoBraceInUnicodeEscape,
+    /// Non-hexadecimal value in '\u{..}'.
+    InvalidCharInUnicodeEscape,
+    /// '\u{}'
+    EmptyUnicodeEscape,
+    /// No closing brace in '\u{..}', e.g. '\u{12'.
+    UnclosedUnicodeEscape,
+    /// '\u{_12}'
+    LeadingUnderscoreUnicodeEscape,
+    /// More than 6 characters in '\u{..}', e.g. '\u{10FFFF_FF}'
+    OverlongUnicodeEscape,
+    /// Invalid in-bound unicode character code, e.g. '\u{DFFF}'.
+    LoneSurrogateUnicodeEscape,
+    /// Out of bounds unicode character code, e.g. '\u{FFFFFF}'.
+    OutOfRangeUnicodeEscape,
+
+    /// Unicode escape code in byte literal.
+    UnicodeEscapeInByte,
+    /// Non-ascii character in byte literal, byte string literal, or raw byte string literal.
+    NonAsciiCharInByte,
+
+    // `\0` in a C string literal.
+    NulInCStr,
+
+    /// After a line ending with '\', the next line contains whitespace
+    /// characters that are not skipped.
+    UnskippedWhitespaceWarning,
+
+    /// After a line ending with '\', multiple lines are skipped.
+    MultipleSkippedLinesWarning,
+}
+
+impl EscapeError {
+    /// Returns true for actual errors, as opposed to warnings.
+    pub fn is_fatal(&self) -> bool {
+        !matches!(
+            self,
+            EscapeError::UnskippedWhitespaceWarning | EscapeError::MultipleSkippedLinesWarning
+        )
+    }
+}
+
+/// Takes the contents of a unicode-only (non-mixed-utf8) literal (without
+/// quotes) and produces a sequence of escaped characters or errors.
+///
+/// Values are returned by invoking `callback`. For `Char` and `Byte` modes,
+/// the callback will be called exactly once.
+pub fn unescape_unicode<F>(src: &str, mode: Mode, callback: &mut F)
+where
+    F: FnMut(Range<usize>, Result<char, EscapeError>),
+{
+    match mode {
+        Char | Byte => {
+            let mut chars = src.chars();
+            let res = unescape_char_or_byte(&mut chars, mode);
+            callback(0..(src.len() - chars.as_str().len()), res);
+        }
+        Str | ByteStr => unescape_non_raw_common(src, mode, callback),
+        RawStr | RawByteStr => check_raw_common(src, mode, callback),
+        RawCStr => check_raw_common(src, mode, &mut |r, mut result| {
+            if let Ok('\0') = result {
+                result = Err(EscapeError::NulInCStr);
+            }
+            callback(r, result)
+        }),
+        CStr => unreachable!(),
+    }
+}
+
+/// Used for mixed utf8 string literals, i.e. those that allow both unicode
+/// chars and high bytes.
+pub enum MixedUnit {
+    /// Used for ASCII chars (written directly or via `\x00`..`\x7f` escapes)
+    /// and Unicode chars (written directly or via `\u` escapes).
+    ///
+    /// For example, if '¥' appears in a string it is represented here as
+    /// `MixedUnit::Char('¥')`, and it will be appended to the relevant byte
+    /// string as the two-byte UTF-8 sequence `[0xc2, 0xa5]`
+    Char(char),
+
+    /// Used for high bytes (`\x80`..`\xff`).
+    ///
+    /// For example, if `\xa5` appears in a string it is represented here as
+    /// `MixedUnit::HighByte(0xa5)`, and it will be appended to the relevant
+    /// byte string as the single byte `0xa5`.
+    HighByte(u8),
+}
+
+impl From<char> for MixedUnit {
+    fn from(c: char) -> Self {
+        MixedUnit::Char(c)
+    }
+}
+
+impl From<u8> for MixedUnit {
+    fn from(n: u8) -> Self {
+        if n.is_ascii() { MixedUnit::Char(n as char) } else { MixedUnit::HighByte(n) }
+    }
+}
+
+/// Takes the contents of a mixed-utf8 literal (without quotes) and produces
+/// a sequence of escaped characters or errors.
+///
+/// Values are returned by invoking `callback`.
+pub fn unescape_mixed<F>(src: &str, mode: Mode, callback: &mut F)
+where
+    F: FnMut(Range<usize>, Result<MixedUnit, EscapeError>),
+{
+    match mode {
+        CStr => unescape_non_raw_common(src, mode, &mut |r, mut result| {
+            if let Ok(MixedUnit::Char('\0')) = result {
+                result = Err(EscapeError::NulInCStr);
+            }
+            callback(r, result)
+        }),
+        Char | Byte | Str | RawStr | ByteStr | RawByteStr | RawCStr => unreachable!(),
+    }
+}
+
+/// Takes a contents of a char literal (without quotes), and returns an
+/// unescaped char or an error.
+pub fn unescape_char(src: &str) -> Result<char, EscapeError> {
+    unescape_char_or_byte(&mut src.chars(), Char)
+}
+
+/// Takes a contents of a byte literal (without quotes), and returns an
+/// unescaped byte or an error.
+pub fn unescape_byte(src: &str) -> Result<u8, EscapeError> {
+    unescape_char_or_byte(&mut src.chars(), Byte).map(byte_from_char)
+}
+
+/// What kind of literal do we parse.
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum Mode {
+    Char,
+
+    Byte,
+
+    Str,
+    RawStr,
+
+    ByteStr,
+    RawByteStr,
+
+    CStr,
+    RawCStr,
+}
+
+impl Mode {
+    pub fn in_double_quotes(self) -> bool {
+        match self {
+            Str | RawStr | ByteStr | RawByteStr | CStr | RawCStr => true,
+            Char | Byte => false,
+        }
+    }
+
+    /// Are `\x80`..`\xff` allowed?
+    fn allow_high_bytes(self) -> bool {
+        match self {
+            Char | Str => false,
+            Byte | ByteStr | CStr => true,
+            RawStr | RawByteStr | RawCStr => unreachable!(),
+        }
+    }
+
+    /// Are unicode (non-ASCII) chars allowed?
+    #[inline]
+    fn allow_unicode_chars(self) -> bool {
+        match self {
+            Byte | ByteStr | RawByteStr => false,
+            Char | Str | RawStr | CStr | RawCStr => true,
+        }
+    }
+
+    /// Are unicode escapes (`\u`) allowed?
+    fn allow_unicode_escapes(self) -> bool {
+        match self {
+            Byte | ByteStr => false,
+            Char | Str | CStr => true,
+            RawByteStr | RawStr | RawCStr => unreachable!(),
+        }
+    }
+
+    pub fn prefix_noraw(self) -> &'static str {
+        match self {
+            Char | Str | RawStr => "",
+            Byte | ByteStr | RawByteStr => "b",
+            CStr | RawCStr => "c",
+        }
+    }
+}
+
+fn scan_escape<T: From<char> + From<u8>>(
+    chars: &mut Chars<'_>,
+    mode: Mode,
+) -> Result<T, EscapeError> {
+    // Previous character was '\\', unescape what follows.
+    let res: char = match chars.next().ok_or(EscapeError::LoneSlash)? {
+        '"' => '"',
+        'n' => '\n',
+        'r' => '\r',
+        't' => '\t',
+        '\\' => '\\',
+        '\'' => '\'',
+        '0' => '\0',
+        'x' => {
+            // Parse hexadecimal character code.
+
+            let hi = chars.next().ok_or(EscapeError::TooShortHexEscape)?;
+            let hi = hi.to_digit(16).ok_or(EscapeError::InvalidCharInHexEscape)?;
+
+            let lo = chars.next().ok_or(EscapeError::TooShortHexEscape)?;
+            let lo = lo.to_digit(16).ok_or(EscapeError::InvalidCharInHexEscape)?;
+
+            let value = (hi * 16 + lo) as u8;
+
+            return if !mode.allow_high_bytes() && !value.is_ascii() {
+                Err(EscapeError::OutOfRangeHexEscape)
+            } else {
+                // This may be a high byte, but that will only happen if `T` is
+                // `MixedUnit`, because of the `allow_high_bytes` check above.
+                Ok(T::from(value))
+            };
+        }
+        'u' => return scan_unicode(chars, mode.allow_unicode_escapes()).map(T::from),
+        _ => return Err(EscapeError::InvalidEscape),
+    };
+    Ok(T::from(res))
+}
+
+fn scan_unicode(chars: &mut Chars<'_>, allow_unicode_escapes: bool) -> Result<char, EscapeError> {
+    // We've parsed '\u', now we have to parse '{..}'.
+
+    if chars.next() != Some('{') {
+        return Err(EscapeError::NoBraceInUnicodeEscape);
+    }
+
+    // First character must be a hexadecimal digit.
+    let mut n_digits = 1;
+    let mut value: u32 = match chars.next().ok_or(EscapeError::UnclosedUnicodeEscape)? {
+        '_' => return Err(EscapeError::LeadingUnderscoreUnicodeEscape),
+        '}' => return Err(EscapeError::EmptyUnicodeEscape),
+        c => c.to_digit(16).ok_or(EscapeError::InvalidCharInUnicodeEscape)?,
+    };
+
+    // First character is valid, now parse the rest of the number
+    // and closing brace.
+    loop {
+        match chars.next() {
+            None => return Err(EscapeError::UnclosedUnicodeEscape),
+            Some('_') => continue,
+            Some('}') => {
+                if n_digits > 6 {
+                    return Err(EscapeError::OverlongUnicodeEscape);
+                }
+
+                // Incorrect syntax has higher priority for error reporting
+                // than unallowed value for a literal.
+                if !allow_unicode_escapes {
+                    return Err(EscapeError::UnicodeEscapeInByte);
+                }
+
+                break std::char::from_u32(value).ok_or({
+                    if value > 0x10FFFF {
+                        EscapeError::OutOfRangeUnicodeEscape
+                    } else {
+                        EscapeError::LoneSurrogateUnicodeEscape
+                    }
+                });
+            }
+            Some(c) => {
+                let digit: u32 = c.to_digit(16).ok_or(EscapeError::InvalidCharInUnicodeEscape)?;
+                n_digits += 1;
+                if n_digits > 6 {
+                    // Stop updating value since we're sure that it's incorrect already.
+                    continue;
+                }
+                value = value * 16 + digit;
+            }
+        };
+    }
+}
+
+#[inline]
+fn ascii_check(c: char, allow_unicode_chars: bool) -> Result<char, EscapeError> {
+    if allow_unicode_chars || c.is_ascii() { Ok(c) } else { Err(EscapeError::NonAsciiCharInByte) }
+}
+
+fn unescape_char_or_byte(chars: &mut Chars<'_>, mode: Mode) -> Result<char, EscapeError> {
+    let c = chars.next().ok_or(EscapeError::ZeroChars)?;
+    let res = match c {
+        '\\' => scan_escape(chars, mode),
+        '\n' | '\t' | '\'' => Err(EscapeError::EscapeOnlyChar),
+        '\r' => Err(EscapeError::BareCarriageReturn),
+        _ => ascii_check(c, mode.allow_unicode_chars()),
+    }?;
+    if chars.next().is_some() {
+        return Err(EscapeError::MoreThanOneChar);
+    }
+    Ok(res)
+}
+
+/// Takes a contents of a string literal (without quotes) and produces a
+/// sequence of escaped characters or errors.
+fn unescape_non_raw_common<F, T: From<char> + From<u8>>(src: &str, mode: Mode, callback: &mut F)
+where
+    F: FnMut(Range<usize>, Result<T, EscapeError>),
+{
+    let mut chars = src.chars();
+    let allow_unicode_chars = mode.allow_unicode_chars(); // get this outside the loop
+
+    // The `start` and `end` computation here is complicated because
+    // `skip_ascii_whitespace` makes us to skip over chars without counting
+    // them in the range computation.
+    while let Some(c) = chars.next() {
+        let start = src.len() - chars.as_str().len() - c.len_utf8();
+        let res = match c {
+            '\\' => {
+                match chars.clone().next() {
+                    Some('\n') => {
+                        // Rust language specification requires us to skip whitespaces
+                        // if unescaped '\' character is followed by '\n'.
+                        // For details see [Rust language reference]
+                        // (https://doc.rust-lang.org/reference/tokens.html#string-literals).
+                        skip_ascii_whitespace(&mut chars, start, &mut |range, err| {
+                            callback(range, Err(err))
+                        });
+                        continue;
+                    }
+                    _ => scan_escape::<T>(&mut chars, mode),
+                }
+            }
+            '"' => Err(EscapeError::EscapeOnlyChar),
+            '\r' => Err(EscapeError::BareCarriageReturn),
+            _ => ascii_check(c, allow_unicode_chars).map(T::from),
+        };
+        let end = src.len() - chars.as_str().len();
+        callback(start..end, res);
+    }
+}
+
+fn skip_ascii_whitespace<F>(chars: &mut Chars<'_>, start: usize, callback: &mut F)
+where
+    F: FnMut(Range<usize>, EscapeError),
+{
+    let tail = chars.as_str();
+    let first_non_space = tail
+        .bytes()
+        .position(|b| b != b' ' && b != b'\t' && b != b'\n' && b != b'\r')
+        .unwrap_or(tail.len());
+    if tail[1..first_non_space].contains('\n') {
+        // The +1 accounts for the escaping slash.
+        let end = start + first_non_space + 1;
+        callback(start..end, EscapeError::MultipleSkippedLinesWarning);
+    }
+    let tail = &tail[first_non_space..];
+    if let Some(c) = tail.chars().next() {
+        if c.is_whitespace() {
+            // For error reporting, we would like the span to contain the character that was not
+            // skipped. The +1 is necessary to account for the leading \ that started the escape.
+            let end = start + first_non_space + c.len_utf8() + 1;
+            callback(start..end, EscapeError::UnskippedWhitespaceWarning);
+        }
+    }
+    *chars = tail.chars();
+}
+
+/// Takes a contents of a string literal (without quotes) and produces a
+/// sequence of characters or errors.
+/// NOTE: Raw strings do not perform any explicit character escaping, here we
+/// only produce errors on bare CR.
+fn check_raw_common<F>(src: &str, mode: Mode, callback: &mut F)
+where
+    F: FnMut(Range<usize>, Result<char, EscapeError>),
+{
+    let mut chars = src.chars();
+    let allow_unicode_chars = mode.allow_unicode_chars(); // get this outside the loop
+
+    // The `start` and `end` computation here matches the one in
+    // `unescape_non_raw_common` for consistency, even though this function
+    // doesn't have to worry about skipping any chars.
+    while let Some(c) = chars.next() {
+        let start = src.len() - chars.as_str().len() - c.len_utf8();
+        let res = match c {
+            '\r' => Err(EscapeError::BareCarriageReturnInRawString),
+            _ => ascii_check(c, allow_unicode_chars),
+        };
+        let end = src.len() - chars.as_str().len();
+        callback(start..end, res);
+    }
+}
+
+#[inline]
+pub fn byte_from_char(c: char) -> u8 {
+    let res = c as u32;
+    debug_assert!(res <= u8::MAX as u32, "guaranteed because of ByteStr");
+    res as u8
+}
diff --git a/compiler/rustc_lexer/src/unescape/tests.rs b/compiler/rustc_lexer/src/unescape/tests.rs
new file mode 100644
index 00000000000..5b99495f475
--- /dev/null
+++ b/compiler/rustc_lexer/src/unescape/tests.rs
@@ -0,0 +1,286 @@
+use super::*;
+
+#[test]
+fn test_unescape_char_bad() {
+    fn check(literal_text: &str, expected_error: EscapeError) {
+        assert_eq!(unescape_char(literal_text), Err(expected_error));
+    }
+
+    check("", EscapeError::ZeroChars);
+    check(r"\", EscapeError::LoneSlash);
+
+    check("\n", EscapeError::EscapeOnlyChar);
+    check("\t", EscapeError::EscapeOnlyChar);
+    check("'", EscapeError::EscapeOnlyChar);
+    check("\r", EscapeError::BareCarriageReturn);
+
+    check("spam", EscapeError::MoreThanOneChar);
+    check(r"\x0ff", EscapeError::MoreThanOneChar);
+    check(r#"\"a"#, EscapeError::MoreThanOneChar);
+    check(r"\na", EscapeError::MoreThanOneChar);
+    check(r"\ra", EscapeError::MoreThanOneChar);
+    check(r"\ta", EscapeError::MoreThanOneChar);
+    check(r"\\a", EscapeError::MoreThanOneChar);
+    check(r"\'a", EscapeError::MoreThanOneChar);
+    check(r"\0a", EscapeError::MoreThanOneChar);
+    check(r"\u{0}x", EscapeError::MoreThanOneChar);
+    check(r"\u{1F63b}}", EscapeError::MoreThanOneChar);
+
+    check(r"\v", EscapeError::InvalidEscape);
+    check(r"\💩", EscapeError::InvalidEscape);
+    check(r"\●", EscapeError::InvalidEscape);
+    check("\\\r", EscapeError::InvalidEscape);
+
+    check(r"\x", EscapeError::TooShortHexEscape);
+    check(r"\x0", EscapeError::TooShortHexEscape);
+    check(r"\xf", EscapeError::TooShortHexEscape);
+    check(r"\xa", EscapeError::TooShortHexEscape);
+    check(r"\xx", EscapeError::InvalidCharInHexEscape);
+    check(r"\xы", EscapeError::InvalidCharInHexEscape);
+    check(r"\x🦀", EscapeError::InvalidCharInHexEscape);
+    check(r"\xtt", EscapeError::InvalidCharInHexEscape);
+    check(r"\xff", EscapeError::OutOfRangeHexEscape);
+    check(r"\xFF", EscapeError::OutOfRangeHexEscape);
+    check(r"\x80", EscapeError::OutOfRangeHexEscape);
+
+    check(r"\u", EscapeError::NoBraceInUnicodeEscape);
+    check(r"\u[0123]", EscapeError::NoBraceInUnicodeEscape);
+    check(r"\u{0x}", EscapeError::InvalidCharInUnicodeEscape);
+    check(r"\u{", EscapeError::UnclosedUnicodeEscape);
+    check(r"\u{0000", EscapeError::UnclosedUnicodeEscape);
+    check(r"\u{}", EscapeError::EmptyUnicodeEscape);
+    check(r"\u{_0000}", EscapeError::LeadingUnderscoreUnicodeEscape);
+    check(r"\u{0000000}", EscapeError::OverlongUnicodeEscape);
+    check(r"\u{FFFFFF}", EscapeError::OutOfRangeUnicodeEscape);
+    check(r"\u{ffffff}", EscapeError::OutOfRangeUnicodeEscape);
+    check(r"\u{ffffff}", EscapeError::OutOfRangeUnicodeEscape);
+
+    check(r"\u{DC00}", EscapeError::LoneSurrogateUnicodeEscape);
+    check(r"\u{DDDD}", EscapeError::LoneSurrogateUnicodeEscape);
+    check(r"\u{DFFF}", EscapeError::LoneSurrogateUnicodeEscape);
+
+    check(r"\u{D800}", EscapeError::LoneSurrogateUnicodeEscape);
+    check(r"\u{DAAA}", EscapeError::LoneSurrogateUnicodeEscape);
+    check(r"\u{DBFF}", EscapeError::LoneSurrogateUnicodeEscape);
+}
+
+#[test]
+fn test_unescape_char_good() {
+    fn check(literal_text: &str, expected_char: char) {
+        assert_eq!(unescape_char(literal_text), Ok(expected_char));
+    }
+
+    check("a", 'a');
+    check("ы", 'ы');
+    check("🦀", '🦀');
+
+    check(r#"\""#, '"');
+    check(r"\n", '\n');
+    check(r"\r", '\r');
+    check(r"\t", '\t');
+    check(r"\\", '\\');
+    check(r"\'", '\'');
+    check(r"\0", '\0');
+
+    check(r"\x00", '\0');
+    check(r"\x5a", 'Z');
+    check(r"\x5A", 'Z');
+    check(r"\x7f", 127 as char);
+
+    check(r"\u{0}", '\0');
+    check(r"\u{000000}", '\0');
+    check(r"\u{41}", 'A');
+    check(r"\u{0041}", 'A');
+    check(r"\u{00_41}", 'A');
+    check(r"\u{4__1__}", 'A');
+    check(r"\u{1F63b}", '😻');
+}
+
+#[test]
+fn test_unescape_str_warn() {
+    fn check(literal: &str, expected: &[(Range<usize>, Result<char, EscapeError>)]) {
+        let mut unescaped = Vec::with_capacity(literal.len());
+        unescape_unicode(literal, Mode::Str, &mut |range, res| unescaped.push((range, res)));
+        assert_eq!(unescaped, expected);
+    }
+
+    // Check we can handle escaped newlines at the end of a file.
+    check("\\\n", &[]);
+    check("\\\n ", &[]);
+
+    check(
+        "\\\n \u{a0} x",
+        &[
+            (0..5, Err(EscapeError::UnskippedWhitespaceWarning)),
+            (3..5, Ok('\u{a0}')),
+            (5..6, Ok(' ')),
+            (6..7, Ok('x')),
+        ],
+    );
+    check("\\\n  \n  x", &[(0..7, Err(EscapeError::MultipleSkippedLinesWarning)), (7..8, Ok('x'))]);
+}
+
+#[test]
+fn test_unescape_str_good() {
+    fn check(literal_text: &str, expected: &str) {
+        let mut buf = Ok(String::with_capacity(literal_text.len()));
+        unescape_unicode(literal_text, Mode::Str, &mut |range, c| {
+            if let Ok(b) = &mut buf {
+                match c {
+                    Ok(c) => b.push(c),
+                    Err(e) => buf = Err((range, e)),
+                }
+            }
+        });
+        assert_eq!(buf.as_deref(), Ok(expected))
+    }
+
+    check("foo", "foo");
+    check("", "");
+    check(" \t\n", " \t\n");
+
+    check("hello \\\n     world", "hello world");
+    check("thread's", "thread's")
+}
+
+#[test]
+fn test_unescape_byte_bad() {
+    fn check(literal_text: &str, expected_error: EscapeError) {
+        assert_eq!(unescape_byte(literal_text), Err(expected_error));
+    }
+
+    check("", EscapeError::ZeroChars);
+    check(r"\", EscapeError::LoneSlash);
+
+    check("\n", EscapeError::EscapeOnlyChar);
+    check("\t", EscapeError::EscapeOnlyChar);
+    check("'", EscapeError::EscapeOnlyChar);
+    check("\r", EscapeError::BareCarriageReturn);
+
+    check("spam", EscapeError::MoreThanOneChar);
+    check(r"\x0ff", EscapeError::MoreThanOneChar);
+    check(r#"\"a"#, EscapeError::MoreThanOneChar);
+    check(r"\na", EscapeError::MoreThanOneChar);
+    check(r"\ra", EscapeError::MoreThanOneChar);
+    check(r"\ta", EscapeError::MoreThanOneChar);
+    check(r"\\a", EscapeError::MoreThanOneChar);
+    check(r"\'a", EscapeError::MoreThanOneChar);
+    check(r"\0a", EscapeError::MoreThanOneChar);
+
+    check(r"\v", EscapeError::InvalidEscape);
+    check(r"\💩", EscapeError::InvalidEscape);
+    check(r"\●", EscapeError::InvalidEscape);
+
+    check(r"\x", EscapeError::TooShortHexEscape);
+    check(r"\x0", EscapeError::TooShortHexEscape);
+    check(r"\xa", EscapeError::TooShortHexEscape);
+    check(r"\xf", EscapeError::TooShortHexEscape);
+    check(r"\xx", EscapeError::InvalidCharInHexEscape);
+    check(r"\xы", EscapeError::InvalidCharInHexEscape);
+    check(r"\x🦀", EscapeError::InvalidCharInHexEscape);
+    check(r"\xtt", EscapeError::InvalidCharInHexEscape);
+
+    check(r"\u", EscapeError::NoBraceInUnicodeEscape);
+    check(r"\u[0123]", EscapeError::NoBraceInUnicodeEscape);
+    check(r"\u{0x}", EscapeError::InvalidCharInUnicodeEscape);
+    check(r"\u{", EscapeError::UnclosedUnicodeEscape);
+    check(r"\u{0000", EscapeError::UnclosedUnicodeEscape);
+    check(r"\u{}", EscapeError::EmptyUnicodeEscape);
+    check(r"\u{_0000}", EscapeError::LeadingUnderscoreUnicodeEscape);
+    check(r"\u{0000000}", EscapeError::OverlongUnicodeEscape);
+
+    check("ы", EscapeError::NonAsciiCharInByte);
+    check("🦀", EscapeError::NonAsciiCharInByte);
+
+    check(r"\u{0}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{000000}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{41}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{0041}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{00_41}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{4__1__}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{1F63b}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{0}x", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{1F63b}}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{FFFFFF}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{ffffff}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{ffffff}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{DC00}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{DDDD}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{DFFF}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{D800}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{DAAA}", EscapeError::UnicodeEscapeInByte);
+    check(r"\u{DBFF}", EscapeError::UnicodeEscapeInByte);
+}
+
+#[test]
+fn test_unescape_byte_good() {
+    fn check(literal_text: &str, expected_byte: u8) {
+        assert_eq!(unescape_byte(literal_text), Ok(expected_byte));
+    }
+
+    check("a", b'a');
+
+    check(r#"\""#, b'"');
+    check(r"\n", b'\n');
+    check(r"\r", b'\r');
+    check(r"\t", b'\t');
+    check(r"\\", b'\\');
+    check(r"\'", b'\'');
+    check(r"\0", b'\0');
+
+    check(r"\x00", b'\0');
+    check(r"\x5a", b'Z');
+    check(r"\x5A", b'Z');
+    check(r"\x7f", 127);
+    check(r"\x80", 128);
+    check(r"\xff", 255);
+    check(r"\xFF", 255);
+}
+
+#[test]
+fn test_unescape_byte_str_good() {
+    fn check(literal_text: &str, expected: &[u8]) {
+        let mut buf = Ok(Vec::with_capacity(literal_text.len()));
+        unescape_unicode(literal_text, Mode::ByteStr, &mut |range, c| {
+            if let Ok(b) = &mut buf {
+                match c {
+                    Ok(c) => b.push(byte_from_char(c)),
+                    Err(e) => buf = Err((range, e)),
+                }
+            }
+        });
+        assert_eq!(buf.as_deref(), Ok(expected))
+    }
+
+    check("foo", b"foo");
+    check("", b"");
+    check(" \t\n", b" \t\n");
+
+    check("hello \\\n     world", b"hello world");
+    check("thread's", b"thread's")
+}
+
+#[test]
+fn test_unescape_raw_str() {
+    fn check(literal: &str, expected: &[(Range<usize>, Result<char, EscapeError>)]) {
+        let mut unescaped = Vec::with_capacity(literal.len());
+        unescape_unicode(literal, Mode::RawStr, &mut |range, res| unescaped.push((range, res)));
+        assert_eq!(unescaped, expected);
+    }
+
+    check("\r", &[(0..1, Err(EscapeError::BareCarriageReturnInRawString))]);
+    check("\rx", &[(0..1, Err(EscapeError::BareCarriageReturnInRawString)), (1..2, Ok('x'))]);
+}
+
+#[test]
+fn test_unescape_raw_byte_str() {
+    fn check(literal: &str, expected: &[(Range<usize>, Result<char, EscapeError>)]) {
+        let mut unescaped = Vec::with_capacity(literal.len());
+        unescape_unicode(literal, Mode::RawByteStr, &mut |range, res| unescaped.push((range, res)));
+        assert_eq!(unescaped, expected);
+    }
+
+    check("\r", &[(0..1, Err(EscapeError::BareCarriageReturnInRawString))]);
+    check("🦀", &[(0..4, Err(EscapeError::NonAsciiCharInByte))]);
+    check("🦀a", &[(0..4, Err(EscapeError::NonAsciiCharInByte)), (4..5, Ok('a'))]);
+}