[PATCH 2 of 6] configitems: add an official API for extensions to register config item

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at octobus.net>
# Date 1497700100 -7200
#      Sat Jun 17 13:48:20 2017 +0200
# Node ID 630aa32cf23b88fa9ab2d7ffac94ecea1307b4c0
# Parent  1b9be14a52e0789ffbaae58252f0b753fe213f86
# EXP-Topic config.register
# Available At https://www.mercurial-scm.org/repo/users/marmoute/mercurial/
#              hg pull https://www.mercurial-scm.org/repo/users/marmoute/mercurial/ -r 630aa32cf23b
configitems: add an official API for extensions to register config item

Extensions can have a 'configtable' mapping and use
'registrar.configitem(table)' to retrieve the registration function.

This behave in the same way as the other way for extensions to register new
items (commands, colors, etc).

diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -13,6 +13,11 @@ from . import (
     error,
 )
 
+def loadconfigtable(ui, extname, configtable):
+    """update config item known to the ui with the extension ones"""
+    for section, items in  configtable.items():
+        ui._knownconfig.setdefault(section, {}).update(items)
+
 class configitem(object):
     """represent a known config item
 
diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -25,6 +25,7 @@ from . import (
     cmdutil,
     color,
     commands,
+    configitems,
     demandimport,
     encoding,
     error,
@@ -736,6 +737,7 @@ def _checkshellalias(lui, ui, args):
 extraloaders = [
     ('cmdtable', commands, 'loadcmdtable'),
     ('colortable', color, 'loadcolortable'),
+    ('configtable', configitems, 'loadconfigtable'),
     ('filesetpredicate', fileset, 'loadpredicate'),
     ('revsetpredicate', revset, 'loadpredicate'),
     ('templatefilter', templatefilters, 'loadfilter'),
diff --git a/mercurial/registrar.py b/mercurial/registrar.py
--- a/mercurial/registrar.py
+++ b/mercurial/registrar.py
@@ -8,11 +8,19 @@
 from __future__ import absolute_import
 
 from . import (
+    configitems,
     error,
     pycompat,
     util,
 )
 
+# unlike the other registered items, config options are neither functions or
+# classes. Registering the option is just small function call.
+#
+# We still add the official API to the registrar module for consistency with
+# the other items extensions want might to register.
+configitem = configitems.getitemregister
+
 class _funcregistrarbase(object):
     """Base of decorator to register a function for specific purpose
 
diff --git a/tests/test-extension.t b/tests/test-extension.t
--- a/tests/test-extension.t
+++ b/tests/test-extension.t
@@ -5,6 +5,9 @@ Test basic extension support
   > from mercurial import commands, registrar
   > cmdtable = {}
   > command = registrar.command(cmdtable)
+  > configtable = {}
+  > configitem = registrar.configitem(configtable)
+  > configitem('tests', 'foo', default="Foo")
   > def uisetup(ui):
   >     ui.write("uisetup called\\n")
   >     ui.flush()
@@ -14,7 +17,9 @@ Test basic extension support
   >     ui.flush()
   > @command('foo', [], 'hg foo')
   > def foo(ui, *args, **kwargs):
-  >     ui.write("Foo\\n")
+  >     foo = ui.config('tests', 'foo')
+  >     ui.write(foo)
+  >     ui.write("\\n")
   > @command('bar', [], 'hg bar', norepo=True)
   > def bar(ui, *args, **kwargs):
   >     ui.write("Bar\\n")