diff mercurial/configitems.py @ 46308:05a1e44b2224

persistent-nodemap: add a revlog.storage.persistent-nodemap.slow-path option

As discussed during the sprint, we want to prevent user to get an unexpected
performance regression when accessing a repository using "persistent-nodemap"
without the associated Rust extension.

We start by adding a config declaration and some documentation.

Since "allow" is the current behavior, we don't need to add any code. The option
possible value will come later.

Note that we already have a `storage.revlog.nodemap.mode` option, but that
option is a bit different. It does some warning and checking at revlog
instantiation time. While we want something done at requirements checking time.

Since we plan for new names and new config value names, we introduce a new
option and will drop the old one later.

Differential Revision: https://phab.mercurial-scm.org/D9758

--- a/mercurial/configitems.py	Thu Jan 14 01:12:42 2021 +0100
+++ b/mercurial/configitems.py	Thu Jan 14 01:25:06 2021 +0100
@@ -1793,6 +1793,14 @@
 coreconfigitem(
     b'storage', b'revlog.nodemap.mode', default=b'compat', experimental=True
 )
+# experimental as long as format.use-persistent-nodemap is.
+coreconfigitem(
+    b'storage',
+    b'revlog.persistent-nodemap.slow-path',
+    default=b"allow",
+    experimental=True,
+)
+
 coreconfigitem(
     b'storage',
     b'revlog.reuse-external-delta',