Add preferences converter

Currently it removes the expanded categories setting, and translates the setting names in the visibility.

Contributes to issue CURA-844.

plugins/VersionUpgrade/VersionUpgrade21to22/Preferences.py

@@ -0,0 +1,61 @@
+# Copyright (c) 2016 Ultimaker B.V.
+# Cura is released under the terms of the AGPLv3 or higher.
+
+import configparser #To read config files.
+import io #To output config files to string.
+
+import UM.VersionUpgrade #To indicate that a file is of the wrong format.
+
+##  Creates a new preferences instance by parsing a serialised preferences file
+#   in version 1 of the file format.
+#
+#   \param serialised The serialised form of a preferences file in version 1.
+#   \return A representation of those preferences, or None if the file format is
+#   incorrect.
+def importFrom(serialised):
+    try:
+        return Preferences(serialised)
+    except (configparser.Error, UM.VersionUpgrade.FormatException, UM.VersionUpgrade.InvalidVersionException):
+        return None
+
+##  A representation of preferences files as intermediary form for conversion
+#   from one format to the other.
+class Preferences:
+    ##  Reads version 2 of the preferences file format, storing it in memory.
+    #
+    #   \param serialised A serialised version 2 preferences file.
+    def __init__(self, serialised):
+        self._config = configparser.ConfigParser(interpolation = None)
+        self._config.read_string(serialised)
+
+        #Checking file correctness.
+        if not self._config.has_section("general"):
+            raise UM.VersionUpgrade.FormatException("No \"general\" section.")
+        if not self._config.has_option("general", "version"):
+            raise UM.VersionUpgrade.FormatException("No \"version\" in \"general\" section.")
+        if int(self._config.get("general", "version")) != 2: # Explicitly hard-code version 2, since if this number changes the programmer MUST change this entire function.
+            raise UM.VersionUpgrade.InvalidVersionException("The version of this preferences file is wrong. It must be 2.")
+
+    ##  Serialises these preferences as a preferences file of version 3.
+    #
+    #   This is where the actual translation happens.
+    #
+    #   \return A serialised version of a preferences file in version 3.
+    def export(self):
+        #Reset the cura/categories_expanded property since it works differently now.
+        if self._config.has_section("cura") and self._config.has_option("cura", "categories_expanded"):
+            self._config.remove_option("cura", "categories_expanded")
+
+        #Translate the setting names in the visible settings.
+        if self._config.has_section("machines") and self._config.has_option("machines", "setting_visibility"):
+            visible_settings = self._config.get("machines", "setting_visibility")
+            visible_settings = visible_settings.split(",")
+            import VersionUpgrade21to22 #Import here to prevent a circular dependency.
+            visible_settings = VersionUpgrade21to22.translateSettingNames(visible_settings)
+            visible_settings = visible_settings.join(",")
+            self._config.set("machines", "setting_visibility", value = visible_settings)
+
+        #Output the result as a string.
+        output = io.StringIO()
+        self._config.write(output)
+        return output.getvalue()