revlog: add glue to use a pure-Rust VFS This will save us a lot of calling back into Python, which is always horribly expensive. We are now faster in all benchmarked cases except for `log --patch` specifically on mozilla-try. Fixing this will happen in a later patch. ``` ### data-env-vars.name = mercurial-devel-2024-03-22-ds2-pnm # benchmark.name = hg.command.cat # bin-env-vars.hg.flavor = rust # bin-env-vars.hg.py-re2-module = default # benchmark.variants.files = all-root # benchmark.variants.output = plain # benchmark.variants.rev = tip e679697a6ca4: 1.760765 ~~~~~ 5559d7e63ec3: 1.555513 (-11.66%, -0.21) ### data-env-vars.name = mozilla-try-2024-03-26-ds2-pnm # benchmark.name = hg.command.cat # bin-env-vars.hg.flavor = rust # bin-env-vars.hg.py-re2-module = default # benchmark.variants.files = all-root # benchmark.variants.output = plain # benchmark.variants.rev = tip e679697a6ca4: 62.848869 ~~~~~ 5559d7e63ec3: 58.113051 (-7.54%, -4.74) ### data-env-vars.name = mozilla-try-2024-03-26-ds2-pnm # benchmark.name = hg.command.log # bin-env-vars.hg.flavor = rust # bin-env-vars.hg.py-re2-module = default # benchmark.variants.limit-rev = 10 # benchmark.variants.patch = yes # benchmark.variants.rev = none e679697a6ca4: 3.173532 ~~~~~ 5559d7e63ec3: 3.543591 (+11.66%, +0.37) ### data-env-vars.name = mozilla-try-2024-03-26-ds2-pnm # benchmark.name = hg.command.log # bin-env-vars.hg.flavor = rust # bin-env-vars.hg.py-re2-module = default # benchmark.variants.limit-rev = 1000 # benchmark.variants.patch = no # benchmark.variants.rev = none e679697a6ca4: 1.214698 ~~~~~ 5559d7e63ec3: 1.192478 (-1.83%, -0.02) ### data-env-vars.name = mozilla-unified-2024-03-22-ds2-pnm # benchmark.name = hg.command.cat # bin-env-vars.hg.flavor = rust # bin-env-vars.hg.py-re2-module = default # benchmark.variants.files = all-root # benchmark.variants.output = plain # benchmark.variants.rev = tip e679697a6ca4: 56.205474 ~~~~~ 5559d7e63ec3: 51.520074 (-8.34%, -4.69) ### data-env-vars.name = mozilla-unified-2024-03-22-ds2-pnm # benchmark.name = hg.command.log # bin-env-vars.hg.flavor = rust # bin-env-vars.hg.py-re2-module = default # benchmark.variants.limit-rev = 10 # benchmark.variants.patch = yes # benchmark.variants.rev = none e679697a6ca4: 2.105419 ~~~~~ 5559d7e63ec3: 2.051849 (-2.54%, -0.05) ### data-env-vars.name = mozilla-unified-2024-03-22-ds2-pnm # benchmark.name = hg.command.log # bin-env-vars.hg.flavor = rust # bin-env-vars.hg.py-re2-module = default # benchmark.variants.limit-rev = 1000 # benchmark.variants.patch = no # benchmark.variants.rev = none e679697a6ca4: 0.309960 ~~~~~ 5559d7e63ec3: 0.299035 (-3.52%, -0.01) ### data-env-vars.name = tryton-public-2024-03-22-ds2-pnm # benchmark.name = hg.command.cat # bin-env-vars.hg.flavor = rust # bin-env-vars.hg.py-re2-module = default # benchmark.variants.files = all-root # benchmark.variants.output = plain # benchmark.variants.rev = tip e679697a6ca4: 1.849832 ~~~~~ 5559d7e63ec3: 1.805076 (-2.42%, -0.04) ### data-env-vars.name = tryton-public-2024-03-22-ds2-pnm # benchmark.name = hg.command.log # bin-env-vars.hg.flavor = rust # bin-env-vars.hg.py-re2-module = default # benchmark.variants.limit-rev = 10 # benchmark.variants.patch = yes # benchmark.variants.rev = none e679697a6ca4: 0.289521 ~~~~~ 5559d7e63ec3: 0.279889 (-3.33%, -0.01) ### data-env-vars.name = tryton-public-2024-03-22-ds2-pnm # benchmark.name = hg.command.log # bin-env-vars.hg.flavor = rust # bin-env-vars.hg.py-re2-module = default # benchmark.variants.limit-rev = 1000 # benchmark.variants.patch = no # benchmark.variants.rev = none e679697a6ca4: 0.332270 ~~~~~ 5559d7e63ec3: 0.323324 (-2.69%, -0.01) ```

--- a/mercurial/revlog.py	Mon Jul 29 20:35:44 2024 +0200
+++ b/mercurial/revlog.py	Mon Jul 29 20:39:34 2024 +0200
@@ -1793,6 +1793,17 @@
             if self._format_version != REVLOGV1:
                 use_rust_index = False
 
+        if hasattr(self.opener, "fncache"):
+            vfs = self.opener.vfs
+            if not self.opener.uses_dotencode:
+                use_rust_index = False
+            if not isinstance(vfs, vfsmod.vfs):
+                # Be cautious since we don't support other vfs
+                use_rust_index = False
+        else:
+            # Rust only supports repos with fncache
+            use_rust_index = False
+
         self._parse_index = parse_index_v1
         if self._format_version == REVLOGV0:
             self._parse_index = revlogv0.parse_index_v0
@@ -1828,8 +1839,26 @@
             default_compression_header = self._docket.default_compression_header
 
         if self.uses_rust:
+            vfs_is_readonly = False
+            fncache = None
+
+            if hasattr(self.opener, "vfs"):
+                vfs = self.opener
+                if isinstance(vfs, vfsmod.readonlyvfs):
+                    vfs_is_readonly = True
+                    vfs = vfs.vfs
+                fncache = vfs.fncache
+                vfs = vfs.vfs
+            else:
+                vfs = self.opener
+
+            vfs_base = vfs.base
+            assert fncache is not None, "Rust only supports repos with fncache"
+
             self._inner = rustrevlog.InnerRevlog(
-                opener=RustVFSWrapper(self.opener),
+                vfs_base=vfs_base,
+                fncache=fncache,
+                vfs_is_readonly=vfs_is_readonly,
                 index_data=index,
                 index_file=self._indexfile,
                 data_file=self._datafile,