[PATCH 3 of 6] configitems: add a devel warning for extensions items overiding core one

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at octobus.net>
# Date 1497808374 -7200
#      Sun Jun 18 19:52:54 2017 +0200
# Node ID 3266463e776f96e2de692de32c3935ad3f752623
# Parent  944f8e3191e6fa37f27d52d3c94d1ef702408ae4
# 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 3266463e776f
configitems: add a devel warning for extensions items overiding core one

We do not want such case to pass silently. In the future we'll likely have
useful tool for an extension to alter the existing definition in core.

diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -16,7 +16,15 @@ from . import (
 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)
+        knownitems = ui._knownconfig.setdefault(section, {})
+        knownkeys = set(knownitems)
+        newkeys = set(items)
+        for key in sorted(knownkeys & newkeys):
+            msg = "extension '%s' overwrite config item '%s.%s'"
+            msg %= (extname, section, key)
+            ui.develwarn(msg, config='warn-config')
+
+        knownitems.update(items)
 
 class configitem(object):
     """represent a known config item
diff --git a/tests/test-devel-warnings.t b/tests/test-devel-warnings.t
--- a/tests/test-devel-warnings.t
+++ b/tests/test-devel-warnings.t
@@ -203,14 +203,26 @@ Test warning on config option access and
   > cmdtable = {}
   > command = registrar.command(cmdtable)
   > 
+  > configtable = {}
+  > configitem = registrar.configitem(configtable)
+  > 
+  > configitem('test', 'some', default='foo')
+  > # overwrite a core config
+  > configitem('ui', 'quiet', default=False)
+  > configitem('ui', 'interactive', default=None)
+  > 
   > @command('buggyconfig')
   > def cmdbuggyconfig(ui, repo):
   >     repo.ui.config('ui', 'quiet', False)
   >     repo.ui.config('ui', 'interactive', None)
+  >     repo.ui.config('test', 'some', 'foo')
   > EOF
 
   $ hg --config "extensions.buggyconfig=${TESTTMP}/buggyconfig.py" buggyconfig
+  devel-warn: extension 'buggyconfig' overwrite config item 'ui.interactive' at: */mercurial/extensions.py:* (loadall) (glob)
+  devel-warn: extension 'buggyconfig' overwrite config item 'ui.quiet' at: */mercurial/extensions.py:* (loadall) (glob)
   devel-warn: specifying a default value for a registered config item: 'ui.quiet' 'False' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
   devel-warn: specifying a default value for a registered config item: 'ui.interactive' 'None' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
+  devel-warn: specifying a default value for a registered config item: 'test.some' 'foo' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
 
   $ cd ..