configitems: relax warning about unwanted default value

The original condition was a bit harsh for extension authors since third-party
extensions need to preserve compatibility with older Mercurial versions, where
no defaults would be loaded from the configtable. So let's silence the warning
if the given default value matches, which should be harmless.

mercurial/ui.py

@@ -471,12 +471,16 b' class ui(object):'
         return value
 
     def _config(self, section, name, default=_unset, untrusted=False):
-        value = default
+        value = itemdefault = default
         item = self._knownconfig.get(section, {}).get(name)
         alternates = [(section, name)]
 
         if item is not None:
             alternates.extend(item.alias)
+            if callable(item.default):
+                itemdefault = item.default()
+            else:
+                itemdefault = item.default
         else:
             msg = ("accessing unregistered config item: '%s.%s'")
             msg %= (section, name)
@@ -490,13 +494,12 b' class ui(object):'
                 msg = "config item requires an explicit default value: '%s.%s'"
                 msg %= (section, name)
                 self.develwarn(msg, 2, 'warn-config-default')
-            elif callable(item.default):
-                    value = item.default()
             else:
-                value = item.default
+                value = itemdefault
         elif (item is not None
-              and item.default is not configitems.dynamicdefault):
-            msg = ("specifying a default value for a registered "
+              and item.default is not configitems.dynamicdefault
+              and default != itemdefault):
+            msg = ("specifying a mismatched default value for a registered "
                    "config item: '%s.%s' '%s'")
             msg %= (section, name, default)
             self.develwarn(msg, 2, 'warn-config-default')

tests/test-devel-warnings.t

@@ -352,17 +352,21 b' Test warning on config option access and'
   > 
   > configitem('test', 'some', default='foo')
   > configitem('test', 'dynamic', default=configitems.dynamicdefault)
+  > configitem('test', 'callable', default=list)
   > # overwrite a core config
   > configitem('ui', 'quiet', default=False)
   > configitem('ui', 'interactive', default=None)
   > 
   > @command(b'buggyconfig')
   > def cmdbuggyconfig(ui, repo):
-  >     repo.ui.config('ui', 'quiet', False)
-  >     repo.ui.config('ui', 'interactive', None)
+  >     repo.ui.config('ui', 'quiet', True)
+  >     repo.ui.config('ui', 'interactive', False)
+  >     repo.ui.config('test', 'some', 'bar')
   >     repo.ui.config('test', 'some', 'foo')
   >     repo.ui.config('test', 'dynamic', 'some-required-default')
   >     repo.ui.config('test', 'dynamic')
+  >     repo.ui.config('test', 'callable', [])
+  >     repo.ui.config('test', 'callable', 'foo')
   >     repo.ui.config('test', 'unregistered')
   >     repo.ui.config('unregistered', 'unregistered')
   > EOF
@@ -370,10 +374,11 b' Test warning on config option access and'
   $ hg --config "extensions.buggyconfig=${TESTTMP}/buggyconfig.py" buggyconfig
   devel-warn: extension 'buggyconfig' overwrite config item 'ui.interactive' at: */mercurial/extensions.py:* (_loadextra) (glob)
   devel-warn: extension 'buggyconfig' overwrite config item 'ui.quiet' at: */mercurial/extensions.py:* (_loadextra) (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)
+  devel-warn: specifying a mismatched default value for a registered config item: 'ui.quiet' 'True' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
+  devel-warn: specifying a mismatched default value for a registered config item: 'ui.interactive' 'False' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
+  devel-warn: specifying a mismatched default value for a registered config item: 'test.some' 'bar' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
   devel-warn: config item requires an explicit default value: 'test.dynamic' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
+  devel-warn: specifying a mismatched default value for a registered config item: 'test.callable' 'foo' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
   devel-warn: accessing unregistered config item: 'test.unregistered' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
   devel-warn: accessing unregistered config item: 'unregistered.unregistered' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)