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Don't union inner literals of repetitions.

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If we do, this results in extracting `foofoofoo` from `(\wfoo){3}`,
which is wrong. This does prevent us from extracting `foofoofoo` from
`foo{3}`, which is unfortunate, but we miss plenty of other stuff too.
Literal extracting needs a good rethink (all the way down into the regex
engine).

Fixes #93
This commit is contained in:
Andrew Gallant
2016-09-25 20:10:28 -04:00
parent a13ac3e3d4
commit 6a8051b258
2 changed files with 15 additions and 5 deletions
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11
grep/src/literals.rs
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@@ -8,7 +8,6 @@ Note that this implementation is incredibly suspicious. We need something more
principled.
*/
use std::cmp;
use std::iter;
use regex::bytes::Regex;
use syntax::{
@@ -181,8 +180,6 @@ fn repeat_range_literals<F: FnMut(&Expr, &mut Literals)>(
lits: &mut Literals,
mut f: F,
) {
use syntax::Expr::*;
if min == 0 {
// This is a bit conservative. If `max` is set, then we could
// treat this as a finite set of alternations. For now, we
@@ -190,8 +187,12 @@ fn repeat_range_literals<F: FnMut(&Expr, &mut Literals)>(
lits.cut();
} else {
let n = cmp::min(lits.limit_size(), min as usize);
let es = iter::repeat(e.clone()).take(n).collect();
f(&Concat(es), lits);
// We only extract literals from a single repetition, even though
// we could do more. e.g., `a{3}` will have `a` extracted instead of
// `aaa`. The reason is that inner literal extraction can't be unioned
// across repetitions. e.g., extracting `foofoofoo` from `(\w+foo){3}`
// is wrong.
f(e, lits);
if n < min as usize {
lits.cut();
}