[Bug 1120322] Re: update-manager crashed with UnboundLocalError in show_diff(): local variable 'line_number' referenced before assignment

[Barry Warsaw]

The odd part is that I'm not sure how to get difflib to produce a diff that
doesn't start with the three lines:

--- blah
+++ blah
@@ blah

to trigger the bug.  This is clearly unexpected in the code (hence the
UnboundLocalError in the first place) and it it definitely not covered in the
test suite.  Hand crafting a call such as this does not trigger the bug:

$ PYTHONPATH=. python3
>>> from aptdaemon.gtk3widgets import DiffView
>>> dv = DiffView()
>>> dv.show_diff('/etc/passwd', '/etc/group')

Without a test, a fix is mostly just conjecture.  I think the best thing
to do is to set `line_number = 0` outside the loop.  This might give you
nonsense but it'll avoid a crash.  I thought about setting it to None
outside the loop, but then the += will still crash, just with a
different one (perhaps we should force that and output some debugging to
better see what's happening, but otoh is it worth it?)

I will attach a branch momentarily.

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https://bugs.launchpad.net/bugs/1120322

Title:
  update-manager crashed with UnboundLocalError in show_diff(): local
  variable 'line_number' referenced before assignment

Status in Aptdaemon:
  Confirmed
Status in “aptdaemon” package in Ubuntu:
  Triaged
Status in “aptdaemon” source package in Precise:
  Triaged

Bug description:
  At the same time as the crash appeared, I got a box for Keep/Renew Steam config file. 
  I was however no able to click on either Keep/Renew.

  ProblemType: Crash
  DistroRelease: Ubuntu 13.04
  Package: update-manager 1:0.181
  ProcVersionSignature: Ubuntu 3.8.0-4.8-generic 3.8.0-rc6
  Uname: Linux 3.8.0-4-generic x86_64
  NonfreeKernelModules: nvidia
  ApportVersion: 2.8-0ubuntu4
  Architecture: amd64
  Date: Sat Feb  9 14:05:09 2013
  ExecutablePath: /usr/bin/update-manager
  GsettingsChanges:
   b'com.ubuntu.update-manager' b'first-run' b'false'
   b'com.ubuntu.update-manager' b'launch-time' b'1360363834'
   b'com.ubuntu.update-manager' b'show-details' b'true'
   b'com.ubuntu.update-manager' b'window-height' b'625'
   b'com.ubuntu.update-manager' b'window-width' b'591'
  InstallationDate: Installed on 2012-08-22 (170 days ago)
  InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
  InterpreterPath: /usr/bin/python3.3
  MarkForUpload: True
  PackageArchitecture: all
  ProcCmdline: /usr/bin/python3 /usr/bin/update-manager
  ProcEnviron:
   LANGUAGE=nb_NO:nb:no_NO:no:nn_NO:nn:en
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=nb_NO.UTF-8
   SHELL=/bin/bash
  PythonArgs: ['/usr/bin/update-manager']
  SourcePackage: update-manager
  Title: update-manager crashed with UnboundLocalError in show_diff(): local variable 'line_number' referenced before assignment
  UpgradeStatus: Upgraded to raring on 2013-01-22 (18 days ago)
  UserGroups: adm cdrom dialout dip lpadmin plugdev sambashare sudo tty

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