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Use memchr for string lexing #9888

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Feb 8, 2024
Merged

Use memchr for string lexing #9888

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128 changes: 94 additions & 34 deletions crates/ruff_python_parser/src/lexer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -690,48 +690,65 @@ impl<'source> Lexer<'source> {

let value_start = self.offset();

let value_end = loop {
match self.cursor.bump() {
Some('\\') => {
if self.cursor.eat_char('\r') {
self.cursor.eat_char('\n');
} else {
self.cursor.bump();
}
}
Some('\r' | '\n') if !triple_quoted => {
let quote_byte = u8::try_from(quote).expect("char that fits in u8");
let value_end = if triple_quoted {
// For triple-quoted strings, scan until we find the closing quote (ignoring escaped
// quotes) or the end of the file.
loop {
let Some(index) = memchr::memchr(quote_byte, self.cursor.rest().as_bytes()) else {
self.cursor.skip_to_end();

if let Some(fstring) = self.fstrings.current() {
// When we are in an f-string, check whether the initial quote
// matches with f-strings quotes and if it is, then this must be a
// missing '}' token so raise the proper error.
if fstring.quote_char() == quote && !fstring.is_triple_quoted() {
if fstring.quote_char() == quote
&& fstring.is_triple_quoted() == triple_quoted
{
return Err(LexicalError {
error: LexicalErrorType::FStringError(
FStringErrorType::UnclosedLbrace,
),
location: self.offset() - TextSize::new(1),
location: self.cursor.text_len(),
});
}
}
return Err(LexicalError {
error: LexicalErrorType::OtherError(
"EOL while scanning string literal".to_owned(),
),
location: self.offset() - TextSize::new(1),
error: LexicalErrorType::Eof,
location: self.cursor.text_len(),
});
};

// Rare case: if there are an odd number of backslashes before the quote, then
// the quote is escaped and we should continue scanning.
let num_backslashes = self.cursor.rest().as_bytes()[..index]
.iter()
.rev()
.take_while(|&&c| c == b'\\')
.count();

// Advance the cursor past the quote and continue scanning.
self.cursor.skip_bytes(index + 1);

// If the character is escaped, continue scanning.
if num_backslashes % 2 == 1 {
continue;
}
Some(c) if c == quote => {
if triple_quoted {
if self.cursor.eat_char2(quote, quote) {
break self.offset() - TextSize::new(3);
}
} else {
break self.offset() - TextSize::new(1);
}

// Otherwise, if it's followed by two more quotes, then we're done.
if self.cursor.eat_char2(quote, quote) {
break self.offset() - TextSize::new(3);
}
}
} else {
// For non-triple-quoted strings, scan until we find the closing quote, but end early
// if we encounter a newline or the end of the file.
loop {
let Some(index) =
memchr::memchr3(quote_byte, b'\r', b'\n', self.cursor.rest().as_bytes())
else {
self.cursor.skip_to_end();

Some(_) => {}
None => {
if let Some(fstring) = self.fstrings.current() {
// When we are in an f-string, check whether the initial quote
// matches with f-strings quotes and if it is, then this must be a
Expand All @@ -748,23 +765,66 @@ impl<'source> Lexer<'source> {
}
}
return Err(LexicalError {
error: if triple_quoted {
LexicalErrorType::Eof
} else {
LexicalErrorType::StringError
},
error: LexicalErrorType::StringError,
location: self.offset(),
});
};

// Rare case: if there are an odd number of backslashes before the quote, then
// the quote is escaped and we should continue scanning.
let num_backslashes = self.cursor.rest().as_bytes()[..index]
.iter()
.rev()
.take_while(|&&c| c == b'\\')
.count();

// Skip up to the current character.
self.cursor.skip_bytes(index);
let ch = self.cursor.bump();

// If the character is escaped, continue scanning.
if num_backslashes % 2 == 1 {
if ch == Some('\r') {
self.cursor.eat_char('\n');
}
continue;
}

match ch {
Some('\r' | '\n') => {
if let Some(fstring) = self.fstrings.current() {
// When we are in an f-string, check whether the initial quote
// matches with f-strings quotes and if it is, then this must be a
// missing '}' token so raise the proper error.
if fstring.quote_char() == quote && !fstring.is_triple_quoted() {
return Err(LexicalError {
error: LexicalErrorType::FStringError(
FStringErrorType::UnclosedLbrace,
),
location: self.offset() - TextSize::new(1),
});
}
}
return Err(LexicalError {
error: LexicalErrorType::OtherError(
"EOL while scanning string literal".to_owned(),
),
location: self.offset() - TextSize::new(1),
});
}
Some(ch) if ch == quote => {
break self.offset() - TextSize::new(1);
}
_ => unreachable!("memchr2 returned an index that is not a quote or a newline"),
}
}
};

let tok = Tok::String {
Ok(Tok::String {
value: self.source[TextRange::new(value_start, value_end)].to_string(),
kind,
triple_quoted,
};
Ok(tok)
})
}

// This is the main entry point. Call this function to retrieve the next token.
Expand Down
5 changes: 5 additions & 0 deletions crates/ruff_python_parser/src/lexer/cursor.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -145,4 +145,9 @@ impl<'a> Cursor<'a> {

self.chars = self.chars.as_str()[count..].chars();
}

/// Skips to the end of the input stream.
pub(super) fn skip_to_end(&mut self) {
self.chars = "".chars();
}
}
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