Inside P2's profile (2) - the fragment matches all osgi bundles

Recently our installer met a strange bug, it didn't uninstall all legacy bundles after updating to new version. Finally I found it's due to a magic fragment is missing in the profile due to some causes.

    <unit id='tooling.osgi.bundle.default' version='1.0.0' singleton='false'>
      <hostRequirements size='1'>
        <required namespace='org.eclipse.equinox.p2.eclipse.type' name='bundle' range='0.0.0' multiple='true' greedy='false'/>
      </hostRequirements>
      <properties size='1'>
        <property name='org.eclipse.equinox.p2.type.fragment' value='true'/>
      </properties>
      <provides size='2'>
        <provided namespace='org.eclipse.equinox.p2.iu' name='tooling.osgi.bundle.default' version='1.0.0'/>
        <provided namespace='org.eclipse.equinox.p2.flavor' name='tooling' version='1.0.0'/>
      </provides>
      <requires size='1'>
        <required namespace='org.eclipse.equinox.p2.eclipse.type' name='bundle' range='0.0.0' multiple='true' greedy='false'/>
      </requires>
      <touchpoint id='null' version='0.0.0'/>
      <touchpointData size='1'>
        <instructions size='4'>
          <instruction key='install'>
            installBundle(bundle:${artifact})
          </instruction>
          <instruction key='uninstall'>
            uninstallBundle(bundle:${artifact})
          </instruction>
          <instruction key='unconfigure'>

          </instruction>
          <instruction key='configure'>
            setStartLevel(startLevel:4);
          </instruction>
        </instructions>
      </touchpointData>
    </unit>

It has 'hostRequirements' element that represents it's a fragment IU and match all the eclipse's plug-ins in that profile. And this fragment defines the touch point actions for its hosts that will do installBundle action during 'install' phrase and uninstallBundle action during 'uninstall' phrase. It's a very good way to remove the duplicate touch point definitions for all eclipse's plug-ins in the profile.

BTW, p2's engine also doesn't attach this fragment to the eclipse's plug-in IU if the top level IU doesn't have the STRICT rule. I'm not sure the root cause of designing for it, but it's the fact.