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//! Group, lookaround and inline-flag parsing.
use super::ast::*;
use super::lexer::TokenKind;
use super::state::Parser;
use crate::error::{Error, ErrorKind, Result, Span};
impl Parser<'_> {
/// Parses a group: (...), (?:...), (?=...), etc.
pub(super) fn parse_group(&mut self) -> Result<Expr> {
let start_span = self.current.span;
self.advance()?; // consume '('
// Check for special group syntax
if matches!(self.current.kind, TokenKind::Question) {
self.advance()?;
match &self.current.kind {
// Non-capturing group (?:...)
TokenKind::Colon => {
self.advance()?;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
Ok(Expr::Group(Box::new(Group {
expr,
kind: GroupKind::NonCapturing,
})))
}
// Named group (?<name>...) or lookbehind (?<=...) (?<!...)
TokenKind::LessThan => {
self.advance()?;
// Check if it's lookbehind or named group
match &self.current.kind {
TokenKind::Equals => {
// (?<=...) positive lookbehind
self.advance()?;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
Ok(Expr::Lookaround(Box::new(Lookaround {
expr,
kind: LookaroundKind::PositiveLookbehind,
})))
}
TokenKind::Exclamation => {
// (?<!...) negative lookbehind
self.advance()?;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
Ok(Expr::Lookaround(Box::new(Lookaround {
expr,
kind: LookaroundKind::NegativeLookbehind,
})))
}
_ => {
// (?<name>...) named group
// The first character of the name is in self.current
let first_char = match &self.current.kind {
TokenKind::Literal(c) => *c,
_ => {
return Err(Error::with_span(
ErrorKind::InvalidGroup,
self.pattern,
self.current.span,
));
}
};
// Read the rest of the identifier
let rest = self.lexer.read_ident_rest();
let name = format!("{}{}", first_char, rest);
self.current = self.lexer.next_token()?;
self.expect(TokenKind::GreaterThan)?;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
let index = self.next_capture;
self.next_capture += 1;
self.capture_count += 1;
Ok(Expr::Group(Box::new(Group {
expr,
kind: GroupKind::NamedCapturing { name, index },
})))
}
}
}
// Lookahead (?=...) or (?!...)
TokenKind::Equals => {
self.advance()?;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
Ok(Expr::Lookaround(Box::new(Lookaround {
expr,
kind: LookaroundKind::PositiveLookahead,
})))
}
TokenKind::Exclamation => {
self.advance()?;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
Ok(Expr::Lookaround(Box::new(Lookaround {
expr,
kind: LookaroundKind::NegativeLookahead,
})))
}
// Python-style named group (?P<name>...)
TokenKind::Literal('P') => {
self.advance()?;
self.expect(TokenKind::LessThan)?;
// The first character of the name is now in self.current
let first_char = match &self.current.kind {
TokenKind::Literal(c) => *c,
_ => {
return Err(Error::with_span(
ErrorKind::InvalidGroup,
self.pattern,
self.current.span,
));
}
};
// Read the rest of the identifier
let rest = self.lexer.read_ident_rest();
let name = format!("{}{}", first_char, rest);
self.current = self.lexer.next_token()?;
self.expect(TokenKind::GreaterThan)?;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
let index = self.next_capture;
self.next_capture += 1;
self.capture_count += 1;
Ok(Expr::Group(Box::new(Group {
expr,
kind: GroupKind::NamedCapturing { name, index },
})))
}
// Flags (?imsx-imsx) or (?imsx:...)
TokenKind::Literal(c) if starts_flag_group(*c) => {
// Flags set by `(?flags:...)` are scoped to the group only, so
// remember the outer flags to restore them afterward. Without
// this, e.g. `'(?i:[sdmt])\p{L}` would leak case-insensitivity
// onto the trailing `\p{L}`.
let saved_flags = self.flags;
self.parse_flags()?;
if matches!(self.current.kind, TokenKind::Colon) {
// (?flags:...) — flags apply only within this group. Record
// the effective flags on the group so the HIR builder can
// scope case-folding/unicode to the body, then restore the
// outer flags for the rest of the pattern.
let group_flags = self.flags;
self.advance()?;
let expr = self.parse_alternation()?;
// Restore before consuming `)`, because consuming it
// lexes the token that follows the group — and under
// extended mode the lexer decides there whether the
// whitespace after `)` is part of the pattern.
self.restore_flags(saved_flags);
self.expect_close_paren(start_span)?;
Ok(Expr::Group(Box::new(Group {
expr,
kind: GroupKind::Flagged(group_flags),
})))
} else if matches!(self.current.kind, TokenKind::CloseParen) {
// (?flags) - just set flags
self.advance()?;
Ok(Expr::Empty)
} else {
Err(Error::with_span(
ErrorKind::InvalidGroup,
self.pattern,
self.current.span,
))
}
}
_ => Err(Error::with_span(
ErrorKind::InvalidGroup,
self.pattern,
self.current.span,
)),
}
} else {
// Regular capturing group
let index = self.next_capture;
self.next_capture += 1;
self.capture_count += 1;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
Ok(Expr::Group(Box::new(Group {
expr,
kind: GroupKind::Capturing(index),
})))
}
}
/// Expects a closing parenthesis.
fn expect_close_paren(&mut self, open_span: Span) -> Result<()> {
if matches!(self.current.kind, TokenKind::CloseParen) {
self.advance()?;
Ok(())
} else {
Err(Error::with_span(
ErrorKind::UnmatchedOpenParen,
self.pattern,
open_span,
))
}
}
/// Parses inline flags.
fn parse_flags(&mut self) -> Result<()> {
let mut negating = false;
loop {
match &self.current.kind {
TokenKind::Literal(c) => match c {
'i' => {
self.flags.case_insensitive = !negating;
self.advance()?;
}
'm' => {
self.flags.multi_line = !negating;
self.advance()?;
}
's' => {
self.flags.dot_all = !negating;
self.advance()?;
}
'x' => {
self.flags.extended = !negating;
// The lexer, not the HIR builder, implements extended
// mode: whitespace and `#` comments are dropped before
// a token exists.
self.lexer.set_extended(self.flags.extended);
self.advance()?;
}
'u' => {
self.flags.unicode = !negating;
self.advance()?;
}
// Outside a character class `-` lexes as a literal, not as
// `Hyphen`, so `(?i-s)` reaches us in this arm.
'-' => {
negating = true;
self.advance()?;
}
_ => break,
},
TokenKind::Hyphen => {
negating = true;
self.advance()?;
}
_ => break,
}
}
Ok(())
}
}
/// Returns true if the character can open a `(?…)` flag group. A leading `-`
/// negates every flag that follows it, as in `(?-i)` or `(?-x:…)`.
fn starts_flag_group(c: char) -> bool {
is_flag_char(c) || c == '-'
}
/// Returns true if the character is a valid flag.
fn is_flag_char(c: char) -> bool {
matches!(c, 'i' | 'm' | 's' | 'x' | 'u')
}