Apply LimitFilter after HiddenTagFilter

The LimitFilter should be performed at the very last step. Instead of
complicating ExpressionCommand and ListCommand to cough up a well
ordered set of filters, order the filters when updating the view. Each
filter is assigned an order number, where filters with a higher order
are applied later.

This fixes the output when using the ls -n flag, where the truncation
appears before the hide tag filter. This results in possibly less items
to be printed than specified (or worse: nothing is printed).

test/test_list_command.py

@@ -26,6 +26,7 @@ from test.command_testcase import CommandTest
 from test.facilities import load_file_to_todolist
 from topydo.commands.ListCommand import ListCommand
 from topydo.lib.Config import config
+from topydo.lib.TodoList import TodoList
 
 # We're searching for 'mock'
 # 'mock' was added as 'unittest.mock' in Python 3.3, but PyPy 3 is based on Python 3.2
@@ -420,6 +421,19 @@ class ListCommandTest(CommandTest):
         self.assertEqual(self.output, "|  1| (C) 2015-11-05 Foo @Context2 Not@Context +Project1 Not+Project\n")
         self.assertEqual(self.errors, "")
 
+    def test_list49(self):
+        """ Only show the top todo. """
+        todolist = TodoList([
+            "This item is hidden h:1",
+            "This item is visible",
+        ])
+
+        command = ListCommand(["-n", "1"], todolist, self.out, self.error)
+        command.execute()
+
+        self.assertEqual(self.output, '|  2| This item is visible\n')
+        self.assertEqual(self.errors, "")
+
     def test_list_name(self):
         name = ListCommand.name()
 

topydo/lib/Filter.py

@@ -32,6 +32,10 @@ class Filter(object):
     def match(self, _):
         raise NotImplementedError
 
+    @property
+    def order(self):
+        return 50
+
 
 class NegationFilter(Filter):
     def __init__(self, p_filter):
@@ -107,6 +111,13 @@ class RelevanceFilter(Filter):
 
         return active and is_due
 
+    @property
+    def order(self):
+        """
+        Perform just after the DependencyFilter, but before any other filters.
+        """
+        return 20
+
 
 class DependencyFilter(Filter):
     """ Matches when a todo has no unfinished child tasks.  """
@@ -130,6 +141,14 @@ class DependencyFilter(Filter):
 
         return not uncompleted
 
+    @property
+    def order(self):
+        """
+        Perform early before any other items are filtered out, possibly
+        breaking the dependency chain.
+        """
+        return 10
+
 
 class InstanceFilter(Filter):
     def __init__(self, p_todos):
@@ -185,6 +204,11 @@ class LimitFilter(Filter):
     def filter(self, p_todos):
         return p_todos[:self.limit] if self.limit >= 0 else p_todos
 
+    @property
+    def order(self):
+        # should be performed at the very last step
+        return 100
+
 _OPERATOR_MATCH = r"(?P<operator><=?|=|>=?|!)?"
 
 

topydo/lib/View.py

@@ -33,7 +33,7 @@ class View(object):
         """ Applies the filters to the list of todo items. """
         result = p_todos
 
-        for _filter in self._filters:
+        for _filter in sorted(self._filters, key=lambda f: f.order):
             result = _filter.filter(result)
 
         return result