solar_parse/lexer/unescape/

mod.rs

//! Utilities for validating string and char literals and turning them into values they represent.

use alloy_primitives::hex;
use solar_ast::Span;
use solar_data_structures::trustme;
use solar_interface::{BytePos, Session};
use std::{borrow::Cow, ops::Range, slice, str::Chars};

mod errors;
pub use errors::EscapeError;
pub(crate) use errors::emit_unescape_error;

pub use solar_ast::StrKind;

pub fn parse_string_literal<'a>(
    src: &'a str,
    kind: StrKind,
    lit_span: Span,
    sess: &Session,
) -> (Cow<'a, [u8]>, bool) {
    let mut has_error = false;
    let content_start = lit_span.lo() + BytePos(1) + BytePos(kind.prefix().len() as u32);
    let bytes = try_parse_string_literal(src, kind, |range, error| {
        has_error = true;
        let (start, end) = (range.start as u32, range.end as u32);
        let lo = content_start + BytePos(start);
        let hi = lo + BytePos(end - start);
        let span = Span::new(lo, hi);
        emit_unescape_error(&sess.dcx, src, span, range, error);
    });
    (bytes, has_error)
}

/// Parses a string literal (without quotes) into a byte array.
/// `f` is called for each escape error.
#[instrument(name = "parse_string_literal", level = "trace", skip_all)]
pub fn try_parse_string_literal<F>(src: &str, kind: StrKind, f: F) -> Cow<'_, [u8]>
where
    F: FnMut(Range<usize>, EscapeError),
{
    let mut bytes = if needs_unescape(src, kind) {
        Cow::Owned(parse_literal_unescape(src, kind, f))
    } else {
        Cow::Borrowed(src.as_bytes())
    };
    if kind == StrKind::Hex {
        // Currently this should never fail, but it's a good idea to check anyway.
        if let Ok(decoded) = hex::decode(&bytes) {
            bytes = Cow::Owned(decoded);
        }
    }
    bytes
}

#[cold]
fn parse_literal_unescape<F>(src: &str, kind: StrKind, f: F) -> Vec<u8>
where
    F: FnMut(Range<usize>, EscapeError),
{
    let mut bytes = Vec::with_capacity(src.len());
    parse_literal_unescape_into(src, kind, f, &mut bytes);
    bytes
}

fn parse_literal_unescape_into<F>(src: &str, kind: StrKind, mut f: F, dst_buf: &mut Vec<u8>)
where
    F: FnMut(Range<usize>, EscapeError),
{
    // `src.len()` is enough capacity for the unescaped string, so we can just use a slice.
    // SAFETY: The buffer is never read from.
    debug_assert!(dst_buf.is_empty());
    debug_assert!(dst_buf.capacity() >= src.len());
    let mut dst = unsafe { slice::from_raw_parts_mut(dst_buf.as_mut_ptr(), dst_buf.capacity()) };
    unescape_literal_unchecked(src, kind, |range, res| match res {
        Ok(c) => {
            // NOTE: We can't use `char::encode_utf8` because `c` can be an invalid unicode code.
            let written = super::utf8::encode_utf8_raw(c, dst).len();

            // SAFETY: Unescaping guarantees that the final unescaped byte array is shorter than
            // the initial string.
            debug_assert!(dst.len() >= written);
            let advanced = unsafe { dst.get_unchecked_mut(written..) };

            // SAFETY: I don't know why this triggers E0521.
            dst = unsafe { trustme::decouple_lt_mut(advanced) };
        }
        Err(e) => f(range, e),
    });
    unsafe { dst_buf.set_len(dst_buf.capacity() - dst.len()) };
}

/// Unescapes the contents of a string literal (without quotes).
///
/// The callback is invoked with a range and either a unicode code point or an error.
#[instrument(level = "debug", skip_all)]
pub fn unescape_literal<F>(src: &str, kind: StrKind, mut callback: F)
where
    F: FnMut(Range<usize>, Result<u32, EscapeError>),
{
    if needs_unescape(src, kind) {
        unescape_literal_unchecked(src, kind, callback)
    } else {
        for (i, ch) in src.char_indices() {
            callback(i..i + ch.len_utf8(), Ok(ch as u32));
        }
    }
}

/// Unescapes the contents of a string literal (without quotes).
///
/// See [`unescape_literal`] for more details.
fn unescape_literal_unchecked<F>(src: &str, kind: StrKind, callback: F)
where
    F: FnMut(Range<usize>, Result<u32, EscapeError>),
{
    match kind {
        StrKind::Str | StrKind::Unicode => {
            unescape_str(src, matches!(kind, StrKind::Unicode), callback)
        }
        StrKind::Hex => unescape_hex_str(src, callback),
    }
}

/// Fast-path check for whether a string literal needs to be unescaped or errors need to be
/// reported.
fn needs_unescape(src: &str, kind: StrKind) -> bool {
    fn needs_unescape_chars(src: &str) -> bool {
        memchr::memchr3(b'\\', b'\n', b'\r', src.as_bytes()).is_some()
    }

    match kind {
        StrKind::Str => needs_unescape_chars(src) || !src.is_ascii(),
        StrKind::Unicode => needs_unescape_chars(src),
        StrKind::Hex => !src.len().is_multiple_of(2) || !hex::check_raw(src),
    }
}

fn scan_escape(chars: &mut Chars<'_>) -> Result<u32, EscapeError> {
    // Previous character was '\\', unescape what follows.
    // https://docs.soliditylang.org/en/latest/grammar.html#a4.SolidityLexer.EscapeSequence
    // Note that hex and unicode escape codes are not validated since string literals are allowed
    // to contain invalid UTF-8.
    Ok(match chars.next().ok_or(EscapeError::LoneSlash)? {
        // Both quotes are always valid escapes.
        '\'' => '\'' as u32,
        '"' => '"' as u32,

        '\\' => '\\' as u32,
        'n' => '\n' as u32,
        'r' => '\r' as u32,
        't' => '\t' as u32,

        'x' => {
            // Parse hexadecimal character code.
            let mut value = 0;
            for _ in 0..2 {
                let d = chars.next().ok_or(EscapeError::HexEscapeTooShort)?;
                let d = d.to_digit(16).ok_or(EscapeError::InvalidHexEscape)?;
                value = value * 16 + d;
            }
            value
        }

        'u' => {
            // Parse hexadecimal unicode character code.
            let mut value = 0;
            for _ in 0..4 {
                let d = chars.next().ok_or(EscapeError::UnicodeEscapeTooShort)?;
                let d = d.to_digit(16).ok_or(EscapeError::InvalidUnicodeEscape)?;
                value = value * 16 + d;
            }
            value
        }

        _ => return Err(EscapeError::InvalidEscape),
    })
}

/// Unescape characters in a string literal.
///
/// See [`unescape_literal`] for more details.
fn unescape_str<F>(src: &str, is_unicode: bool, mut callback: F)
where
    F: FnMut(Range<usize>, Result<u32, EscapeError>),
{
    let mut chars = src.chars();
    // 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('\r') if chars.clone().nth(1) == Some('\n') => {
                    // +2 for the '\\' and '\r' characters.
                    skip_ascii_whitespace(&mut chars, start + 2, &mut callback);
                    continue;
                }
                Some('\n') => {
                    // +1 for the '\\' character.
                    skip_ascii_whitespace(&mut chars, start + 1, &mut callback);
                    continue;
                }
                _ => scan_escape(&mut chars),
            },
            '\n' => Err(EscapeError::StrNewline),
            '\r' => {
                if chars.clone().next() == Some('\n') {
                    continue;
                }
                Err(EscapeError::BareCarriageReturn)
            }
            c if !is_unicode && !c.is_ascii() => Err(EscapeError::StrNonAsciiChar),
            c => Ok(c as u32),
        };
        let end = src.len() - chars.as_str().len();
        callback(start..end, res);
    }
}

/// Skips over whitespace after a "\\\n" escape sequence.
///
/// Reports errors if multiple newlines are encountered.
fn skip_ascii_whitespace<F>(chars: &mut Chars<'_>, mut start: usize, callback: &mut F)
where
    F: FnMut(Range<usize>, Result<u32, EscapeError>),
{
    // Skip the first newline.
    let mut nl = chars.next();
    if let Some('\r') = nl {
        nl = chars.next();
    }
    debug_assert_eq!(nl, Some('\n'));
    let mut tail = chars.as_str();
    start += 1;

    while tail.starts_with(|c: char| c.is_ascii_whitespace()) {
        let first_non_space =
            tail.bytes().position(|b| !matches!(b, b' ' | b'\t')).unwrap_or(tail.len());
        tail = &tail[first_non_space..];
        start += first_non_space;

        if let Some(tail2) = tail.strip_prefix('\n').or_else(|| tail.strip_prefix("\r\n")) {
            let skipped = tail.len() - tail2.len();
            tail = tail2;
            callback(start..start + skipped, Err(EscapeError::CannotSkipMultipleLines));
            start += skipped;
        }
    }
    *chars = tail.chars();
}

/// Unescape characters in a hex string literal.
///
/// See [`unescape_literal`] for more details.
fn unescape_hex_str<F>(src: &str, mut callback: F)
where
    F: FnMut(Range<usize>, Result<u32, EscapeError>),
{
    let mut chars = src.char_indices();
    if src.starts_with("0x") || src.starts_with("0X") {
        chars.next();
        chars.next();
        callback(0..2, Err(EscapeError::HexPrefix));
    }

    let count = chars.clone().filter(|(_, c)| c.is_ascii_hexdigit()).count();
    if !count.is_multiple_of(2) {
        callback(0..src.len(), Err(EscapeError::HexOddDigits));
        return;
    }

    let mut emit_underscore_errors = true;
    let mut allow_underscore = false;
    let mut even = true;
    for (start, c) in chars {
        let res = match c {
            '_' => {
                if emit_underscore_errors && (!allow_underscore || !even) {
                    // Don't spam errors for multiple underscores.
                    emit_underscore_errors = false;
                    Err(EscapeError::HexBadUnderscore)
                } else {
                    allow_underscore = false;
                    continue;
                }
            }
            c if !c.is_ascii_hexdigit() => Err(EscapeError::HexNotHexDigit),
            c => Ok(c as u32),
        };

        if res.is_ok() {
            even = !even;
            allow_underscore = true;
        }

        let end = start + c.len_utf8();
        callback(start..end, res);
    }

    if emit_underscore_errors && src.len() > 1 && src.ends_with('_') {
        callback(src.len() - 1..src.len(), Err(EscapeError::HexBadUnderscore));
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use EscapeError::*;

    type ExErr = (Range<usize>, EscapeError);

    fn check(kind: StrKind, src: &str, expected_str: &str, expected_errs: &[ExErr]) {
        let panic_str = format!("{kind:?}: {src:?}");

        let mut ok = String::with_capacity(src.len());
        let mut errs = Vec::with_capacity(expected_errs.len());
        unescape_literal(src, kind, |range, c| match c {
            Ok(c) => ok.push(char::try_from(c).unwrap()),
            Err(e) => errs.push((range, e)),
        });
        assert_eq!(errs, expected_errs, "{panic_str}");
        assert_eq!(ok, expected_str, "{panic_str}");

        let mut errs2 = Vec::with_capacity(errs.len());
        let out = try_parse_string_literal(src, kind, |range, e| {
            errs2.push((range, e));
        });
        assert_eq!(errs2, errs, "{panic_str}");
        if kind == StrKind::Hex {
            assert_eq!(hex::encode(out), expected_str, "{panic_str}");
        } else {
            assert_eq!(hex::encode(out), hex::encode(expected_str), "{panic_str}");
        }
    }

    #[test]
    fn unescape_str() {
        let cases: &[(&str, &str, &[ExErr])] = &[
            ("", "", &[]),
            (" ", " ", &[]),
            ("\t", "\t", &[]),
            (" \t ", " \t ", &[]),
            ("foo", "foo", &[]),
            ("hello world", "hello world", &[]),
            (r"\", "", &[(0..1, LoneSlash)]),
            (r"\\", "\\", &[]),
            (r"\\\", "\\", &[(2..3, LoneSlash)]),
            (r"\\\\", "\\\\", &[]),
            (r"\\ ", "\\ ", &[]),
            (r"\\ \", "\\ ", &[(3..4, LoneSlash)]),
            (r"\\ \\", "\\ \\", &[]),
            (r"\x", "", &[(0..2, HexEscapeTooShort)]),
            (r"\x1", "", &[(0..3, HexEscapeTooShort)]),
            (r"\xz", "", &[(0..3, InvalidHexEscape)]),
            (r"\xzf", "f", &[(0..3, InvalidHexEscape)]),
            (r"\xzz", "z", &[(0..3, InvalidHexEscape)]),
            (r"\x69", "\x69", &[]),
            (r"\xE8", "è", &[]),
            (r"\u", "", &[(0..2, UnicodeEscapeTooShort)]),
            (r"\u1", "", &[(0..3, UnicodeEscapeTooShort)]),
            (r"\uz", "", &[(0..3, InvalidUnicodeEscape)]),
            (r"\uzf", "f", &[(0..3, InvalidUnicodeEscape)]),
            (r"\u12", "", &[(0..4, UnicodeEscapeTooShort)]),
            (r"\u123", "", &[(0..5, UnicodeEscapeTooShort)]),
            (r"\u1234", "\u{1234}", &[]),
            (r"\u00e8", "è", &[]),
            (r"\r", "\r", &[]),
            (r"\t", "\t", &[]),
            (r"\n", "\n", &[]),
            (r"\n\n", "\n\n", &[]),
            (r"\ ", "", &[(0..2, InvalidEscape)]),
            (r"\?", "", &[(0..2, InvalidEscape)]),
            ("\r\n", "", &[(1..2, StrNewline)]),
            ("\n", "", &[(0..1, StrNewline)]),
            ("\\\n", "", &[]),
            ("\\\na", "a", &[]),
            ("\\\n  a", "a", &[]),
            ("a \\\n  b", "a b", &[]),
            ("a\\n\\\n  b", "a\nb", &[]),
            ("a\\t\\\n  b", "a\tb", &[]),
            ("a\\n \\\n  b", "a\n b", &[]),
            ("a\\n \\\n \tb", "a\n b", &[]),
            ("a\\t \\\n  b", "a\t b", &[]),
            ("\\\n \t a", "a", &[]),
            (" \\\n \t a", " a", &[]),
            ("\\\n \t a\n", "a", &[(6..7, StrNewline)]),
            ("\\\n   \t   ", "", &[]),
            (" \\\n   \t   ", " ", &[]),
            (" he\\\n \\\nllo \\\n wor\\\nld", " hello world", &[]),
            ("\\\n\na\\\nb", "ab", &[(2..3, CannotSkipMultipleLines)]),
            ("\\\n \na\\\nb", "ab", &[(3..4, CannotSkipMultipleLines)]),
            (
                "\\\n \n\na\\\nb",
                "ab",
                &[(3..4, CannotSkipMultipleLines), (4..5, CannotSkipMultipleLines)],
            ),
            (
                "a\\\n \n \t \nb\\\nc",
                "abc",
                &[(4..5, CannotSkipMultipleLines), (8..9, CannotSkipMultipleLines)],
            ),
        ];
        for &(src, expected_str, expected_errs) in cases {
            check(StrKind::Str, src, expected_str, expected_errs);
            check(StrKind::Unicode, src, expected_str, expected_errs);
        }
    }

    #[test]
    fn unescape_unicode_str() {
        let cases: &[(&str, &str, &[ExErr], &[ExErr])] = &[
            ("è", "è", &[], &[(0..2, StrNonAsciiChar)]),
            ("😀", "😀", &[], &[(0..4, StrNonAsciiChar)]),
        ];
        for &(src, expected_str, e1, e2) in cases {
            check(StrKind::Unicode, src, expected_str, e1);
            check(StrKind::Str, src, "", e2);
        }
    }

    #[test]
    fn unescape_hex_str() {
        let cases: &[(&str, &str, &[ExErr])] = &[
            ("", "", &[]),
            ("z", "", &[(0..1, HexNotHexDigit)]),
            ("\n", "", &[(0..1, HexNotHexDigit)]),
            ("  11", "11", &[(0..1, HexNotHexDigit), (1..2, HexNotHexDigit)]),
            ("0x", "", &[(0..2, HexPrefix)]),
            ("0X", "", &[(0..2, HexPrefix)]),
            ("0x11", "11", &[(0..2, HexPrefix)]),
            ("0X11", "11", &[(0..2, HexPrefix)]),
            ("1", "", &[(0..1, HexOddDigits)]),
            ("12", "12", &[]),
            ("123", "", &[(0..3, HexOddDigits)]),
            ("1234", "1234", &[]),
            ("_", "", &[(0..1, HexBadUnderscore)]),
            ("_11", "11", &[(0..1, HexBadUnderscore)]),
            ("_11_", "11", &[(0..1, HexBadUnderscore)]),
            ("11_", "11", &[(2..3, HexBadUnderscore)]),
            ("11_22", "1122", &[]),
            ("11__", "11", &[(3..4, HexBadUnderscore)]),
            ("11__22", "1122", &[(3..4, HexBadUnderscore)]),
            ("1_2", "12", &[(1..2, HexBadUnderscore)]),
        ];
        for &(src, expected_str, expected_errs) in cases {
            check(StrKind::Hex, src, expected_str, expected_errs);
        }
    }
}