showconfig: don't accept multiple sections and one config item

Showconfig now behaves as documented and only accepts one section.name argument
or a number of section names.

mercurial/commands.py

@@ -1066,7 +1066,9 b' def showconfig(ui, repo, *values, **opts'
         ui.debug(_('read config from: %s\n') % f)
     untrusted = bool(opts.get('untrusted'))
     if values:
-        if len([v for v in values if '.' in v]) > 1:
+        sections = [v for v in values if '.' not in v]
+        items = [v for v in values if '.' in v]
+        if len(items) > 1 or items and sections:
             raise util.Abort(_('only one config item permitted'))
     for section, name, value in ui.walkconfig(untrusted=untrusted):
         sectname = section + '.' + name

tests/test-hgrc.t

@@ -75,6 +75,22 b' username expansion'
   $ HGUSER=$olduser
   $ export HGUSER
 
+showconfig with multiple arguments
+
+  $ echo "[alias]" > $HGRCPATH
+  $ echo "log = log -g" >> $HGRCPATH
+  $ echo "[defaults]" >> $HGRCPATH
+  $ echo "identify = -n" >> $HGRCPATH
+  $ hg showconfig alias defaults
+  alias.log=log -g
+  defaults.identify=-n
+  $ hg showconfig alias defaults.identify
+  abort: only one config item permitted
+  [255]
+  $ hg showconfig alias.log defaults.identify
+  abort: only one config item permitted
+  [255]
+
 HGPLAIN
 
   $ cd ..