view source functionality should be more robust against buggy activities

[rgs]

Scenario:

We added view-source support to TurtleArt (see attached code snippet). I manage to hit a code path (a race condition somewhere or problem accessing the temp file) in which I got the following exception (in ~/.sugar/default/logs/shell.log):

File "/usr/lib/python2.6/dist-packages/jarabe/view/viewsource.py",  line 291, in __init__
 activity_button.props.group = document_button
 UnboundLocalError: local variable 'document_button' referenced before assignment

Checking the constructor of the Toolbar class in jarabe/view/viewsource.py it seems like the following test:

 if document_path is not None:

forgets to check file existence as the previous conditional does:

 if document_path is not None and os.path.exists(document_path)

The attached patch proposes a fix by starting document_button to None which seems cheaper then testing for the existence of a file twice.

[erikos]

Thanks for submitting the patch! I marked the ticket 'r?', as I guess you want to add it to the review queue. (  http://wiki.sugarlabs.org/go/Development_Team/Code_Review )

[tomeu]

Looks great to me, thanks!

Simon, can you add Raul to the Sugar committers?

[erikos]

I have added Raul to the Sugar committers. And pushed the patch:
 http://git.sugarlabs.org/projects/sugar/repos/mainline/commits/da1be6e637b636f16e476a00b07e64164609c1a9

Thanks Raul!