rust-re2: add wrapper for calling Re2 from Rust This assumes that Re2 is installed following Google's guide. I am not sure how we want to integrate it in the project, but I think a follow-up patch would be more appropriate for such work. As it stands, *not* having Re2 installed results in a compilation error, which is a problem as it breaks install compatibility. Hence, this is gated behind a non-default `with-re2` compilation feature. Differential Revision: https://phab.mercurial-scm.org/D7910

--- a/rust/hg-core/src/lib.rs	Thu Jan 16 11:27:12 2020 +0100
+++ b/rust/hg-core/src/lib.rs	Thu Jan 16 13:34:04 2020 +0100
@@ -21,6 +21,8 @@
 pub mod matchers;
 pub mod revlog;
 pub use revlog::*;
+#[cfg(feature = "with-re2")]
+pub mod re2;
 pub mod utils;
 
 use crate::utils::hg_path::{HgPathBuf, HgPathError};