Use an enum for user model roles.

qutebrowser/models/basecompletion.py

@@ -18,13 +18,16 @@
 """The base completion model for completion in the command line.
 
 Module attributes:
-    ROLE_MARKS: The role index used for marks.
+    Role: An enum of user defined model roles.
 """
 
 from PyQt5.QtCore import Qt
 from PyQt5.QtGui import QStandardItemModel, QStandardItem
 
-ROLE_MARKS = Qt.UserRole
+from qutebrowser.utils.usertypes import enum
+
+
+Role = enum('marks', 'sort', start=Qt.UserRole)
 
 
 class NoCompletionsError(Exception):
@@ -77,7 +80,7 @@ class BaseCompletionModel(QStandardItemModel):
         """
         haystack = self.data(index)
         marks = self._get_marks(needle, haystack)
-        self.setData(index, marks, ROLE_MARKS)
+        self.setData(index, marks, Role.marks)
 
     def new_category(self, name):
         """Add a new category to the model.

qutebrowser/widgets/completion.py

@@ -38,7 +38,7 @@ class CompletionView(QTreeView):
     Based on QTreeView but heavily customized so root elements show as category
     headers, and children show as flat list.
 
-    Highlights completions based on marks in the ROLE_MARKS data.
+    Highlights completions based on marks in the Role.marks data.
 
     Class attributes:
         STYLESHEET: The stylesheet template for the CompletionView.

qutebrowser/widgets/completiondelegate.py

@@ -27,7 +27,7 @@ from PyQt5.QtGui import (QIcon, QPalette, QTextDocument, QTextOption,
                          QTextCursor, QColor, QAbstractTextDocumentLayout)
 
 import qutebrowser.config.config as config
-from qutebrowser.models.basecompletion import ROLE_MARKS
+from qutebrowser.models.basecompletion import Role
 from qutebrowser.config.style import get_stylesheet
 
 
@@ -188,7 +188,7 @@ class CompletionItemDelegate(QStyledItemDelegate):
         self._doc.setDocumentMargin(2)
 
         if index.column() == 0:
-            marks = index.data(ROLE_MARKS)
+            marks = index.data(Role.marks)
             if marks is None:
                 return
             for mark in marks: