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Andrew Gallant bd222ae93f regex: fix HIR analysis bug
An alternate can be empty at this point, so we must handle it. We didn't
before because the regex engine actually disallows empty alternates,
however, this code runs before the regex compiler rejects the regex.
2019-04-14 19:29:27 -04:00

128 lines
3.8 KiB
Rust

use aho_corasick::{AhoCorasick, AhoCorasickBuilder, MatchKind};
use grep_matcher::{Matcher, Match, NoError};
use regex_syntax::hir::Hir;
use error::Error;
use matcher::RegexCaptures;
/// A matcher for an alternation of literals.
///
/// Ideally, this optimization would be pushed down into the regex engine, but
/// making this work correctly there would require quite a bit of refactoring.
/// Moreover, doing it one layer above lets us do thing like, "if we
/// specifically only want to search for literals, then don't bother with
/// regex parsing at all."
#[derive(Clone, Debug)]
pub struct MultiLiteralMatcher {
/// The Aho-Corasick automaton.
ac: AhoCorasick,
}
impl MultiLiteralMatcher {
/// Create a new multi-literal matcher from the given literals.
pub fn new<B: AsRef<[u8]>>(
literals: &[B],
) -> Result<MultiLiteralMatcher, Error> {
let ac = AhoCorasickBuilder::new()
.match_kind(MatchKind::LeftmostFirst)
.auto_configure(literals)
.build_with_size::<usize, _, _>(literals)
.map_err(Error::regex)?;
Ok(MultiLiteralMatcher { ac })
}
}
impl Matcher for MultiLiteralMatcher {
type Captures = RegexCaptures;
type Error = NoError;
fn find_at(
&self,
haystack: &[u8],
at: usize,
) -> Result<Option<Match>, NoError> {
match self.ac.find(&haystack[at..]) {
None => Ok(None),
Some(m) => Ok(Some(Match::new(at + m.start(), at + m.end()))),
}
}
fn new_captures(&self) -> Result<RegexCaptures, NoError> {
Ok(RegexCaptures::simple())
}
fn capture_count(&self) -> usize {
1
}
fn capture_index(&self, _: &str) -> Option<usize> {
None
}
fn captures_at(
&self,
haystack: &[u8],
at: usize,
caps: &mut RegexCaptures,
) -> Result<bool, NoError> {
caps.set_simple(None);
let mat = self.find_at(haystack, at)?;
caps.set_simple(mat);
Ok(mat.is_some())
}
// We specifically do not implement other methods like find_iter. Namely,
// the iter methods are guaranteed to be correct by virtue of implementing
// find_at above.
}
/// Alternation literals checks if the given HIR is a simple alternation of
/// literals, and if so, returns them. Otherwise, this returns None.
pub fn alternation_literals(expr: &Hir) -> Option<Vec<Vec<u8>>> {
use regex_syntax::hir::{HirKind, Literal};
// This is pretty hacky, but basically, if `is_alternation_literal` is
// true, then we can make several assumptions about the structure of our
// HIR. This is what justifies the `unreachable!` statements below.
if !expr.is_alternation_literal() {
return None;
}
let alts = match *expr.kind() {
HirKind::Alternation(ref alts) => alts,
_ => return None, // one literal isn't worth it
};
let extendlit = |lit: &Literal, dst: &mut Vec<u8>| {
match *lit {
Literal::Unicode(c) => {
let mut buf = [0; 4];
dst.extend_from_slice(c.encode_utf8(&mut buf).as_bytes());
}
Literal::Byte(b) => {
dst.push(b);
}
}
};
let mut lits = vec![];
for alt in alts {
let mut lit = vec![];
match *alt.kind() {
HirKind::Empty => {}
HirKind::Literal(ref x) => extendlit(x, &mut lit),
HirKind::Concat(ref exprs) => {
for e in exprs {
match *e.kind() {
HirKind::Literal(ref x) => extendlit(x, &mut lit),
_ => unreachable!("expected literal, got {:?}", e),
}
}
}
_ => unreachable!("expected literal or concat, got {:?}", alt),
}
lits.push(lit);
}
Some(lits)
}