extensions: warn about invalid extensions when listing disabled commands

Invalid extensions in hgext/ could in some cases cause a crash when searching
for unknown commands in disabled extensions.

With this change we issue a warning if extracting commands from the extensions
fails. Traceback is available on request.

Reported on https://bugzilla.redhat.com/show_bug.cgi?id=663183 with forest.py.

mercurial/commands.py

@@ -2034,7 +2034,7 b' def help_(ui, name=None, with_version=Fa'
                        'extensions\n'))
 
     def helpextcmd(name):
-        cmd, ext, mod = extensions.disabledcmd(name, ui.config('ui', 'strict'))
+        cmd, ext, mod = extensions.disabledcmd(ui, name, ui.config('ui', 'strict'))
         doc = gettext(mod.__doc__).splitlines()[0]
 
         msg = help.listexts(_("'%s' is provided by the following "

mercurial/extensions.py

@@ -248,7 +248,7 b' def disabledext(name):'
     if name in paths:
         return _disabledhelp(paths[name])
 
-def disabledcmd(cmd, strict=False):
+def disabledcmd(ui, cmd, strict=False):
     '''import disabled extensions until cmd is found.
     returns (cmdname, extname, doc)'''
 
@@ -266,6 +266,10 b' def disabledcmd(cmd, strict=False):'
                 getattr(mod, 'cmdtable', {}), strict)
         except (error.AmbiguousCommand, error.UnknownCommand):
             return
+        except Exception:
+            ui.warn(_('warning: error finding commands in %s\n') % path)
+            ui.traceback()
+            return
         for c in aliases:
             if c.startswith(cmd):
                 cmd = c

tests/test-extension.t

@@ -315,6 +315,11 b' Broken disabled extension and command:'
   
   use "hg help extensions" for information on enabling extensions
 
+  $ cat > hgext/forest.py <<EOF
+  > cmdtable = None
+  > EOF
   $ hg --config extensions.path=./path.py help foo > /dev/null
+  warning: error finding commands in $TESTTMP/hgext/forest.py
   hg: unknown command 'foo'
+  warning: error finding commands in $TESTTMP/hgext/forest.py
   [255]