Tool.getSortedImportSteps should return a deterministic order

[tseaver]

In https://bugs.launchpad.net/zope-cmf-buildout/+bug/1418881, Dieter Maurer reported:

Products.GenericSetup 1.7.3

"GenericSetup" supports the declaration of step dependencies and "getSortedImportSteps" returns a sequence of steps respecting those declarations. However, the step order is otherwise non-deterministic. This makes it extremely hard to detect missing step dependency declarations.

https://dev.plone.org/ticket/13815 shows an example where a missing step dependency was not recognized for a very long time.

I have spent the last few days to track down another similar problem: I start Zope and get the following (unworking) sort order:

2015-02-05T08:50:19 INFO bfd.theme_bp.utilities.tracing Return Products.GenericSetup.tool.getSortedImportSteps -> (u'plone-difftool', u'plone.app.caching', u'properties', u'Products.Ploneboard.uninstallVarious', u'rolemap', u'sharing', u'ploneopenid-various', u'collective.z3cform.datetimewidget_various', u'toolset', u'reference_catalog', u'various', u'typeinfo', u'cmfeditions_various', u'repositorytool', u'kupu-setup', u'workflow', u'update-workflow-rolemap', u'placeful_workflow', u'placeful_marker', u'catalog', u'content', u'cookie_authentication', u'caching_policy_mgr', u'various-calendar', u'plone.app.theming', u'uid_catalog', u'componentregistry', u'portlets', u'contentrules', u'atcttool', u'factorytool', u'actions', u'plonetheme.sunburst-various', u'controlpanel', u'memberdata-properties', u'plonepas', u'mailhost', u'action-icons', u'solr', u'browserlayer', u'content_type_registry', u'mimetypes-registry-various', u'kss_mimetype', u'difftool', u'tinymce_various', u'plone.app.registry', u'tinymce_settings', u'plone-final', u'plone-content', u'skins', u'jsregistry', u'bfd.gui.various', u'cssregistry', u'jquerytools-various', u'kssregistry', u'propertiestool', u'viewlets', u'archetypes-various', u'archetypetool', u'plone_outputfilters_various'

I restart Zope (without any modification) and get the following (working) sort order:

2015-02-05T08:55:18 INFO bfd.theme_bp.utilities.tracing Return Products.GenericSetup.tool.getSortedImportSteps -> (u'properties', u'rolemap', u'sharing', u'toolset', u'uid_catalog', u'various-calendar', u'plone.app.theming', u'various', u'componentregistry', u'plone_outputfilters_various', u'action-icons', u'memberdata-properties', u'skins', u'bfd.gui.various', u'kssregistry', u'cssregistry', u'jquerytools-various', u'jsregistry', u'tinymce_settings', u'tinymce_various', u'browserlayer', u'content_type_registry', u'mimetypes-registry-various', u'kss_mimetype', u'mailhost', u'propertiestool', u'actions', u'plonetheme.sunburst-various', u'controlpanel', u'plonepas', u'viewlets', u'difftool', u'plone.app.registry', u'solr', u'archetypes-various', u'archetypetool', u'catalog', u'atcttool', u'cookie_authentication', u'typeinfo', u'factorytool', u'kupu-setup', u'cmfeditions_various', u'repositorytool', u'reference_catalog', u'caching_policy_mgr', u'workflow', u'content', u'portlets', u'plone-final', u'plone-content', u'contentrules', u'placeful_workflow', u'placeful_marker', u'update-workflow-rolemap', u'ploneopenid-various', u'collective.z3cform.datetimewidget_various', u'Products.Ploneboard.uninstallVarious', u'plone-difftool', u'plone.app.caching', u'ploneboard-various')

Of course, the real problem are missing dependency declarations for the Plone "plone-final" import step (it depends on "skins"). However, the non deterministic behaviour of "getSortedImportSteps" hides this problem quite efficiently.