Duplicate line in preseed causes exception

[Max Brustkern]

Right now if you pass in a preseed with a duplicated line, an exception is generated. I tried just this as the preseed:
d-i clock-setup/utc boolean true
d-i clock-setup/utc boolean true
And I got:
PYTHONPATH=/home/max/bzr/merges/bug1043419 run_utah_tests.py -i /var/cache/utah/iso/ubuntu-12.04-alternate-i386.iso -g 4 -g 4 -n /usr/share/utah/client/examples/pass.run -d -p q
INFO: Installing client deb on machine
INFO: Provisioning VM
INFO: Loading VM
INFO: Creating custom virtual machine
INFO: Preparing kernel
INFO: Unpacking kernel from image
INFO: Preparing initrd
INFO: Unpacking initrd from image
INFO: Unpacking initrd
INFO: Copying ssh public key
INFO: Creating latecommand script
INFO: Setting up preseed
Traceback (most recent call last):
  File "/usr/bin/run_utah_tests.py", line 120, in <module>
    run_utah_tests()
  File "/usr/bin/run_utah_tests.py", line 106, in run_utah_tests
    function(args=args)
  File "/usr/share/utah/examples/run_install_test.py", line 96, in run_install_test
    exitstatus, locallogs = run_tests(args, machine)
  File "/home/max/bzr/merges/bug1043419/utah/run.py", line 32, in run_tests
    machine.installclient()
  File "/home/max/bzr/merges/bug1043419/utah/provisioning/provisioning.py", line 268, in installclient
    self.uploadfiles([clientdeb], tmppath)
  File "/home/max/bzr/merges/bug1043419/utah/provisioning/provisioning.py", line 521, in uploadfiles
    self.activecheck()
  File "/home/max/bzr/merges/bug1043419/utah/provisioning/vm/libvirtvm.py", line 93, in activecheck
    self.provisioncheck()
  File "/home/max/bzr/merges/bug1043419/utah/provisioning/provisioning.py", line 223, in provisioncheck
    utah.timeout.timeout(config.installtimeout, self._provision)
  File "/home/max/bzr/merges/bug1043419/utah/timeout.py", line 47, in timeout
    retval = command(*args, **kw)
  File "/home/max/bzr/merges/bug1043419/utah/provisioning/vm/libvirtvm.py", line 66, in _provision
    self._create()
  File "/home/max/bzr/merges/bug1043419/utah/provisioning/vm/libvirtvm.py", line 641, in _create
    self._setuppreseed(tmpdir=tmpdir)
  File "/home/max/bzr/merges/bug1043419/utah/provisioning/provisioning.py", line 776, in _setuppreseed
    preseed = Preseed(self.preseed)
  File "/home/max/bzr/merges/bug1043419/utah/preseed.py", line 16, in __init__
    self.read(filename)
  File "/home/max/bzr/merges/bug1043419/utah/preseed.py", line 60, in read
    new_section = Section.new(self, output_lines)
  File "/home/max/bzr/merges/bug1043419/utah/preseed.py", line 174, in new
    return ConfigurationSection(parent, lines)
  File "/home/max/bzr/merges/bug1043419/utah/preseed.py", line 311, in __init__
    self.qname = splitted_text[1]
  File "/home/max/bzr/merges/bug1043419/utah/preseed.py", line 243, in __set__
    obj.property_updated(self.name, old_value, new_value)
  File "/home/max/bzr/merges/bug1043419/utah/preseed.py", line 352, in property_updated
    self.parent.section_updated(self, property_name, old_value, new_value)
  File "/home/max/bzr/merges/bug1043419/utah/preseed.py", line 136, in section_updated
    assert new_text not in self._qnames
AssertionError

[Javier Collado (javier.collado)]

@Max

The preseed parser assumes that the question name is unique for two reasons:
- access the quickly to a section in the preseed using a dictionary
- identify each section by question name (so that it's easy to update the preseed)

For example, to get the late command line, the code is:
question = preseed['preseed/late_command']

If there were multiple late commands, we'd need to do something like this:
question = preseed['preseed/late_command'][index]

I'm not sure about what's the behavior for a preseed file when a line is duplicated. Is just the last line that one that is valid?

In such a case, I could do a couple of things:
- use only the last line, that is, keep the code as it's and just make changes to the last line
- the same as above, but remove duplicates when the final preseed is written to a file

For now, in my opinion isn't a bad thing to have an exception for duplicated question names since I thing that's possible a mistake, but if there's a use case I'm missing please let me know. Anyway, any of the fixes above would be easy to write.

[Max Brustkern (nuclearbob)]

That makes sense. Could we maybe update the assert to indicate to the user that a duplicate line in the preseed is what's causing the error? I had to do some digging to figure that out.