Blacklist transitional/dummy stub packages from import

Their short description reliably says so (e.g. 'transitional
package', 'transitional dummy package for foo'). Verified against
production package data: 190 matches, none of them ever had a
screenshot.

lib/tasks/import_debian.rake

@@ -35,6 +35,14 @@ BLACKLIST_SECTION_PATTERN = [
   %r{/?libs$},
 ]
 
+# List of regular expressions. If the package's short description
+# matches any of these then the package will not be imported.
+# Transitional/dummy stub packages exist only to ease upgrades to a
+# renamed or split package and never get a useful screenshot.
+BLACKLIST_DESCRIPTION_PATTERN = [
+  /transitional/i,
+]
+
 # Whether to delete a blacklisted package from the database
 REMOVE_BLACKLISTED_PACKAGE = true
 
@@ -87,7 +95,9 @@ namespace :debshots do
             Rails.logger.info "> Package: #{package[:Package]}"
             #Rails.logger.debug "Fetching package informaton from the database"
 
-            if package_name_blacklisted? package[:Package] or package_section_blacklisted? package[:Section]
+            if package_name_blacklisted?(package[:Package]) or
+               package_section_blacklisted?(package[:Section]) or
+               package_description_blacklisted?(package[:Description])
               # Should the package get removed from the database?
               if REMOVE_BLACKLISTED_PACKAGE
                 db_package = Package.find_by name: package[:Package]
@@ -280,3 +290,16 @@ def package_section_blacklisted?(section)
   end
   return false
 end
+
+# Check if a package's short description marks it as a transitional or
+# dummy stub package (e.g. "transitional package", "transitional dummy
+# package for foo"). These never get a useful screenshot.
+def package_description_blacklisted?(description)
+  BLACKLIST_DESCRIPTION_PATTERN.each do |pattern|
+    if description.to_s =~ pattern
+      Rails.logger.debug "  > Blacklisted by description ('#{description}' matches '#{pattern}')"
+      return true
+    end
+  end
+  false
+end