rust-regex: increase the DFA size limit for the `regex` crate
`re2`'s DFA limit is already increased in `rust/hg-core/src/re2/rust_re2.cpp`,
the same has to be done for the `regex` crate.
Big repositories with big `.hgignore`s will sometimes hit this limit and face
extreme performance regressions (I've seen one take *minutes* for `hg status`).
Differential Revision: https://phab.mercurial-scm.org/D8499
--- a/rust/hg-core/src/matchers.rs Fri May 01 21:47:39 2020 +0530
+++ b/rust/hg-core/src/matchers.rs Thu May 07 10:15:19 2020 +0200
@@ -358,6 +358,10 @@
let pattern_string = unsafe { String::from_utf8_unchecked(escaped_bytes) };
let re = regex::bytes::RegexBuilder::new(&pattern_string)
.unicode(false)
+ // Big repos with big `.hgignore` will hit the default limit and
+ // incur a significant performance hit. One repo's `hg status` hit
+ // multiple *minutes*.
+ .dfa_size_limit(50 * (1 << 20))
.build()
.map_err(|e| PatternError::UnsupportedSyntax(e.to_string()))?;