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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.
///
/// Wrapped in [`Parser::with_nesting`] since every `(` is one nesting
/// level, regardless of which group flavor it turns out to be — that
/// covers the mutual recursion back through `parse_alternation` at every
/// one of this function's call sites into it.
pub(super) fn parse_group(&mut self) -> Result<Expr> {
self.with_nesting(Self::parse_group_inner)
}
/// Dispatches on the group's flavor. Each branch lives in its own
/// function so the frame held across the recursion carries only this
/// dispatch — see [`DEFAULT_NEST_LIMIT`](super::DEFAULT_NEST_LIMIT).
fn parse_group_inner(&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.parse_non_capturing_group(start_span),
// Named group (?<name>...) or lookbehind (?<=...) (?<!...)
TokenKind::LessThan => self.parse_angle_group(start_span),
// Atomic group (?>...): deliberately unsupported, since
// regexr's engines are linear-time and never backtrack, so
// there is nothing for an atomic group to bound.
TokenKind::GreaterThan => Err(Error::with_span(
ErrorKind::AtomicGroup,
self.pattern,
start_span,
)),
// Lookahead (?=...) or (?!...)
TokenKind::Equals => {
self.parse_lookaround(start_span, LookaroundKind::PositiveLookahead)
}
TokenKind::Exclamation => {
self.parse_lookaround(start_span, LookaroundKind::NegativeLookahead)
}
// Note: `(?#...)` inline comments never reach the parser as
// tokens — the lexer recognizes `(?#` as a unit at the point
// `(` is scanned (see `Lexer::next_token`) and consumes the
// whole construct itself, so it behaves identically in every
// mode, including extended (`x`) mode.
// Python-style named group (?P<name>...), or a named
// backreference to one, (?P=name).
TokenKind::Literal('P') => self.parse_python_group(start_span),
// Quote-delimited named group (?'name'...), equivalent to
// (?<name>...) and (?P<name>...).
TokenKind::Literal('\'') => self.parse_quoted_named_group(start_span),
// Flags (?imsx-imsx) or (?imsx:...)
TokenKind::Literal(c) if starts_flag_group(*c) => self.parse_flag_group(start_span),
_ => Err(Error::with_span(
ErrorKind::InvalidGroup,
self.pattern,
self.current.span,
)),
}
} else {
self.parse_capturing_group(start_span)
}
}
/// `(?:...)`, positioned on the `:`.
#[inline(never)]
fn parse_non_capturing_group(&mut self, start_span: Span) -> Result<Expr> {
self.advance()?;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
Ok(group(expr, GroupKind::NonCapturing))
}
/// A lookahead or lookbehind body, positioned on the `=`/`!` that opens
/// it. Both directions differ only in the node they build.
#[inline(never)]
fn parse_lookaround(&mut self, start_span: Span, kind: LookaroundKind) -> Result<Expr> {
self.advance()?;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
Ok(Expr::Lookaround(Box::new(Lookaround { expr, kind })))
}
/// `(?<...`: a lookbehind (`(?<=`, `(?<!`) or a named group `(?<name>`,
/// positioned on the `<`.
#[inline(never)]
fn parse_angle_group(&mut self, start_span: Span) -> Result<Expr> {
self.advance()?;
// Check if it's lookbehind or named group
match &self.current.kind {
TokenKind::Equals => {
self.parse_lookaround(start_span, LookaroundKind::PositiveLookbehind)
}
TokenKind::Exclamation => {
self.parse_lookaround(start_span, LookaroundKind::NegativeLookbehind)
}
// (?<name>...) named group.
// The first character of the name is in self.current
_ => self.parse_named_group_body(start_span, TokenKind::GreaterThan),
}
}
/// The `name>...)` tail shared by `(?<name>...)` and `(?P<name>...)`,
/// positioned on the name's first character. `terminator` is the token
/// that closes the name.
#[inline(never)]
fn parse_named_group_body(&mut self, start_span: Span, terminator: TokenKind) -> Result<Expr> {
let name = self.parse_group_name()?;
self.expect(terminator)?;
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
Ok(self.finish_named_group(name, expr))
}
/// `(?P<name>...)` or the `(?P=name)` backreference, positioned on the `P`.
#[inline(never)]
fn parse_python_group(&mut self, start_span: Span) -> Result<Expr> {
self.advance()?;
match &self.current.kind {
TokenKind::LessThan => {
self.advance()?;
// The first character of the name is now in self.current
self.parse_named_group_body(start_span, TokenKind::GreaterThan)
}
// (?P=name) - named backreference, Python style.
TokenKind::Equals => {
self.advance()?;
let name_span = self.current.span;
let name = self.parse_group_name()?;
self.expect(TokenKind::CloseParen)?;
match self.named_groups.get(&name) {
Some(&index) => Ok(Expr::Backref(index)),
None => Err(Error::with_span(
ErrorKind::UnknownGroupName(name),
self.pattern,
name_span,
)),
}
}
_ => Err(Error::with_span(
ErrorKind::InvalidGroup,
self.pattern,
self.current.span,
)),
}
}
/// `(?'name'...)`, positioned on the opening quote.
#[inline(never)]
fn parse_quoted_named_group(&mut self, start_span: Span) -> Result<Expr> {
self.advance()?;
// An immediate closing quote means an empty name, which
// `parse_group_name` cannot detect on its own: `'` lexes
// to the same `Literal` token kind as any other name
// character, so it would otherwise be read as content.
if matches!(self.current.kind, TokenKind::Literal('\'')) {
return Err(Error::with_span(
ErrorKind::InvalidGroup,
self.pattern,
self.current.span,
));
}
let name = self.parse_group_name()?;
match self.current.kind {
TokenKind::Literal('\'') => {
self.advance()?;
}
_ => {
return Err(Error::with_span(
ErrorKind::InvalidGroup,
self.pattern,
self.current.span,
));
}
}
let expr = self.parse_alternation()?;
self.expect_close_paren(start_span)?;
Ok(self.finish_named_group(name, expr))
}
/// Registers a parsed named group and builds its node. Shared by every
/// named-group spelling so they cannot drift in capture numbering.
fn finish_named_group(&mut self, name: String, expr: Expr) -> Expr {
let index = self.next_capture;
self.next_capture += 1;
self.capture_count += 1;
self.named_groups.insert(name.clone(), index);
group(expr, GroupKind::NamedCapturing { name, index })
}
/// `(?flags)` or `(?flags:...)`, positioned on the first flag character.
#[inline(never)]
fn parse_flag_group(&mut self, start_span: Span) -> Result<Expr> {
// 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(group(expr, 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,
))
}
}
/// A plain `(...)` capturing group, positioned on its first body token.
#[inline(never)]
fn parse_capturing_group(&mut self, start_span: Span) -> Result<Expr> {
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(group(expr, GroupKind::Capturing(index)))
}
/// Parses a group name from the token stream: `self.current` must
/// already hold the name's first character (lexed as a `Literal`), and
/// the rest is read straight off the lexer's raw character stream via
/// `read_ident_rest`. Shared by every named-group spelling —
/// `(?<name>...)`, `(?P<name>...)`, `(?'name'...)` — and by the
/// `(?P=name)` backreference, so the name syntax (and its malformed-name
/// error) is identical across all of them. Does not consume the
/// construct's closing delimiter; callers check that themselves, since
/// it differs per spelling (`>`, `'`, or `)`).
fn parse_group_name(&mut self) -> Result<String> {
let first_char = match &self.current.kind {
TokenKind::Literal(c) => *c,
_ => {
return Err(Error::with_span(
ErrorKind::InvalidGroup,
self.pattern,
self.current.span,
));
}
};
let rest = self.lexer.read_ident_rest();
let name = format!("{}{}", first_char, rest);
self.current = self.lexer.next_token()?;
Ok(name)
}
/// 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(())
}
}
/// Builds a group node. Kept out of line so the boxing adds no slots to the
/// caller's frame, which is held across the nesting recursion.
#[inline(never)]
fn group(expr: Expr, kind: GroupKind) -> Expr {
Expr::Group(Box::new(Group { expr, kind }))
}
/// 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')
}