1 /// re2 module

     2 ///

     3 /// The Python implementation of Mercurial uses the Re2 regex engine when

     4 /// possible and if the bindings are installed, falling back to Python's `re`

     5 /// in case of unsupported syntax (Re2 is a non-backtracking engine).

     6 ///

     7 /// Using it from Rust is not ideal. We need C++ bindings, a C++ compiler,

     8 /// Re2 needs to be installed... why not just use the `regex` crate?

     9 ///

    10 /// Using Re2 from the Rust implementation guarantees backwards compatibility.

    11 /// We know it will work out of the box without needing to figure out the

    12 /// subtle differences in syntax. For example, `regex` currently does not

    13 /// support empty alternations (regex like `a||b`) which happens more often

    14 /// than we might think. Old benchmarks also showed worse performance from

    15 /// regex than with Re2, but the methodology and results were lost, so take

    16 /// this with a grain of salt.

    17 ///

    18 /// The idea is to use Re2 for now as a temporary phase and then investigate

    19 /// how much work would be needed to use `regex`.

    20 mod re2;

    21 pub use re2::Re2;