Add validator for machine names

Currently this validator can't be used in QML due to a PyQt bug. I plan to call the validator manually upon receiving a signal that the text changed in a text box.

Contributes to issue CURA-2692.

cura/Settings/MachineNameValidator.py

@@ -0,0 +1,33 @@
+# Copyright (c) 2016 Ultimaker B.V.
+# Cura is released under the terms of the AGPLv3 or higher.
+
+import UM.Resources
+import UM.Settings.ContainerRegistry
+import UM.Settings.InstanceContainer
+
+from PyQt5.QtGui import QValidator
+import os #For statvfs.
+import urllib #To escape machine names for how they're saved to file.
+
+##  Are machine names valid?
+#
+#   Performs checks based on the length of the name.
+class MachineNameValidator(QValidator):
+    ##  Check if a specified machine name is allowed.
+    #
+    #   \param name The machine name to check.
+    #   \param position The current position of the cursor in the text box.
+    #   \return ``QValidator.Invalid`` if it's disallowed, or
+    #   ``QValidator.Acceptable`` if it's allowed.
+    def validate(self, name, position):
+        #Check for file name length of the current settings container (which is the longest file we're saving with the name).
+        try:
+            filename_max_length = os.statvfs(UM.Resources.getDataStoragePath())
+        except AttributeError: #Doesn't support statvfs. Probably because it's not a Unix system.
+            filename_max_length = 255 #Assume it's Windows on NTFS.
+        escaped_name = urllib.parse.quote_plus(name)
+        current_settings_filename = escaped_name + "_current_settings." + UM.Settings.ContainerRegistry.getMimeTypeForContainer(UM.Settings.InstanceContainer).preferredSuffix
+        if current_settings_filename > filename_max_length:
+            return QValidator.Invalid
+
+        return QValidator.Acceptable #All checks succeeded.

cura/Settings/__init__.py

@@ -8,6 +8,7 @@ from .CuraContainerRegistry import CuraContainerRegistry
 from .ExtruderManager import ExtruderManager
 from .ExtrudersModel import ExtrudersModel
 from .MachineManager import MachineManager
+from .MachineNameValidator import MachineNameValidator
 from .MaterialSettingsVisibilityHandler import MaterialSettingsVisibilityHandler
 from .SettingOverrideDecorator import SettingOverrideDecorator
 from .QualitySettingsModel import QualitySettingsModel