nodemap: move and update the commend about persistence being experimental

The comment was at the wrong place (on the developer option instead of the
activation switch). So we move it at the right location and update it.

Differential Revision: https://phab.mercurial-scm.org/D8420

mercurial/configitems.py

@@ -405,18 +405,6 b' coreconfigitem('
 coreconfigitem(
     b'devel', b'legacy.exchange', default=list,
 )
-# TODO before getting `persistent-nodemap` out of experimental
-#
-# * decide for a "status" of the persistent nodemap and associated location
-#   - part of the store next the revlog itself (new requirements)
-#   - part of the cache directory
-#   - part of an `index` directory
-#     (https://www.mercurial-scm.org/wiki/ComputedIndexPlan)
-# * do we want to use this for more than just changelog? if so we need:
-#   - simpler "pending" logic for them
-#   - double check the memory story (we dont want to keep all revlog in memory)
-#   - think about the naming scheme if we are in "cache"
-# * increment the version format to "1" and freeze it.
 coreconfigitem(
     b'devel', b'persistent-nodemap', default=False,
 )
@@ -783,6 +771,9 b' coreconfigitem('
 coreconfigitem(
     b'format', b'usestore', default=True,
 )
+# Right now, the only efficient implement of the nodemap logic is in Rust, so
+# the persistent nodemap feature needs to stay experimental as long as the Rust
+# extensions are an experimental feature.
 coreconfigitem(
     b'format', b'use-persistent-nodemap', default=False, experimental=True
 )