rust-ignore: construct regex Hir object directly, avoiding large regex string Rework how we convert patterns to regexes in rust. Instead of going patterns -> string -> Regex, which is slow and causes some correctness issues, build a structured regex_syntax::hir::Hir value, which is faster and it also prevents surprising regex escape. This change makes the time of `build_regex_match` go from ~70-80ms to ~40ms in my testing (for a large hgignore). The bug I mentioned involves regex patterns that "escape" their intended scope. For example, a sequence of hgignore regexp patterns like this would previously lead to surprising behavior: foo(?: bar baz ) this matches foobar and foobaz, and doesn't match bar and baz. The new behavior is to report a pattern parse error The Python hg also has this bug, so this bugfix not really helping much, but it's probably better to fall back to real Python bugs than to simulate them.