Properties of type "v" and structs cause a traceback and aren't shown in the UI

[Daniel Manrique]

Our project is presenting a dbus service exposing some objects which have a
property of type "v" (variant). On the Python side, those contain a tuple of a
string and two integers. So the "container" has dbus_signature="v" and the
content is put together like this:

dbus.Struct([
                filename,
                line_start,
                line_end
            ], signature=dbus.Signature("(suu)"))

When I attempt to look at this property in d-feet, I get the following
exception:

Traceback (most recent call last):
File "/usr/lib/python2.7/dist-packages/dfeet/introspection.py", line 104, in __treeview_row_activated_cb
    model[iter_][0] = obj.markup_str
  File "/usr/lib/python2.7/dist-packages/dfeet/introspection_helper.py", line 87, in markup_str
    s += " = %s" % (self.value)
TypeError: not all arguments converted during string formatting

One of my colleagues figured out that the string formatting in line 87 is
missing a comma (single-element tuple syntax is botched). If I change line 87
to read:

    s += " = %s" % (self.value, )

then things work as expected and d-feet is able to properly show the variant
data in the UI.

While looking at this in more detail, I noticed that basically anything that uses a struct will be affected, see the reproduction case below.

This was observed on d-feet 0.3.3 on an Ubuntu 13.04 system, I also checked and
the code is still like this in the upstream repository git://git.gnome.org/d-feet, so I assume the
problem is still present. On the git repository, however, the troublesome tuple
has moved to line 90.

The bug is reported upstream here:

https://bugzilla.gnome.org/show_bug.cgi?id=702593

Steps to reproduce:
- Install and launch d-feet on an Ubuntu 13.04 system, on a terminal so console output can be seen.
- Select the "session bus" tab (top right).
- On the search field, type "org.gnome.zeitgeist.engine".
- On the list of objects (right pane), expand /org/gnome/zeitgeist/log/activity (last one)
- Under this, expand org.gnome.zeitgeist.Log
- At the very end of the list of exposed properties/methods, double-click on "Array of [String] extensions (read)". The list of extensions will be loaded and shown immediately to the right of the field description and type. This is expected behavior.
- Double-click on "Struct of (Int32, Int32, Int32) version (read)".

Expected behavior:
- The version should be shown next to the field type/description, as with the "extensions" field above.

Actual behavior:
- Nothing is shown.
- Trace visible in the console:

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/dfeet/introspection.py", line 104, in __treeview_row_activated_cb
    model[iter_][0] = obj.markup_str
  File "/usr/lib/python2.7/dist-packages/dfeet/introspection_helper.py", line 87, in markup_str
    s += " = %s" % (self.value)
TypeError: not all arguments converted during string formatting

======
ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: d-feet 0.3.3-1
ProcVersionSignature: Ubuntu 3.8.0-23.34-generic 3.8.11
Uname: Linux 3.8.0-23-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.9.2-0ubuntu8.1
Architecture: amd64
Date: Tue Jun 18 15:07:05 2013
EcryptfsInUse: Yes
InstallationDate: Installed on 2013-04-25 (53 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MarkForUpload: True
PackageArchitecture: all
SourcePackage: d-feet
UpgradeStatus: No upgrade log present (probably fresh install)