revlog: add the glue to use the Rust `InnerRevlog` from Python The performance of this has been looked at for quite some time, and some workflows are actually quite a bit faster than with the Python + C code. However, we are still (up to 20%) slower in some crucial places like cloning certain repos, log, cat, which makes this an incomplete rewrite. This is mostly due to the high amount of overhead in Python <-> Rust FFI, especially around the VFS code. A future patch series will rewrite the VFS code in pure Rust, which should hopefully get us up to par with current perfomance, if not better in all important cases. This is a "save state" of sorts, as this is a ton of code, and I don't want to pile up even more things in a single review. Continuing to try to match the current performance will take an extremely long time, if it's not impossible, without the aforementioned VFS work.

--- a/mercurial/vfs.py	Wed Jun 19 17:03:13 2024 +0200
+++ b/mercurial/vfs.py	Wed Jun 19 19:10:49 2024 +0200
@@ -82,6 +82,10 @@
     # encoded vfs (see issue6546)
     _dir_sep: bytes = b'/'
 
+    # Used to disable the Rust `InnerRevlog` in case the VFS is not supported
+    # by the Rust code
+    rust_compatible = True
+
     # TODO: type return, which is util.posixfile wrapped by a proxy
     @abc.abstractmethod
     def __call__(self, path: bytes, mode: bytes = b'rb', **kwargs) -> Any: