branchcache: add a "pure topological head" fast path
In a narrow but actually quick common case, all topological heads are all on
the same branch and all open. In this case, computing the branch map is very
simple. We can quickly detect situation where this situation will not change.
So we update the V3 format to be able to express this situation and upgrade the
update code to detect we remains in that mode.
The branch cache is populated with the actual value when the branch map is
accessed, but the update_disk method can do the update without needing to
populate it.
Mercurial has the ability to add new features through the use of
extensions. Extensions may add new commands, add options to
existing commands, change the default behavior of commands, or
implement hooks.
To enable the "foo" extension, either shipped with Mercurial or in the
Python search path, create an entry for it in your configuration file,
like this::
[extensions]
foo =
You may also specify the full path to an extension::
[extensions]
myfeature = ~/.hgext/myfeature.py
See :hg:`help config` for more information on configuration files.
Extensions are not loaded by default for a variety of reasons:
they can increase startup overhead; they may be meant for advanced
usage only; they may provide potentially dangerous abilities (such
as letting you destroy or modify history); they might not be ready
for prime time; or they may alter some usual behaviors of stock
Mercurial. It is thus up to the user to activate extensions as
needed.
To explicitly disable an extension enabled in a configuration file of
broader scope, prepend its path with !::
[extensions]
# disabling extension bar residing in /path/to/extension/bar.py
bar = !/path/to/extension/bar.py
# ditto, but no path was supplied for extension baz
baz = !