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//! 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
}