Fix negation of ordinal tag filters

When an ordinal tag filter is negated (i.e. -id:1), then this isn't seen
as a negation but as an ordinal tag filter with tag -id and value 1.
Which isn't likely to exist, resulting in every todo item to be excluded
from the result.

test/test_list_command.py

@@ -314,6 +314,14 @@ class ListCommandTest(CommandTest):
         self.assertEqual(self.output, "")
         self.assertEqual(self.errors, "option -z not recognized\n")
 
+    def test_list42(self):
+        command = ListCommand(["-x", "+Project1", "-id:1"], self.todolist, self.out,
+            self.error)
+        command.execute()
+
+        self.assertEqual(self.output, "|  1| (C) 2015-11-05 Foo @Context2 Not@Context +Project1 Not+Project\n")
+        self.assertEqual(self.errors, "")
+
     def test_help(self):
         command = ListCommand(["help"], self.todolist, self.out, self.error)
         command.execute()

topydo/lib/ExpressionCommand.py

@@ -54,17 +54,20 @@ class ExpressionCommand(Command):
                 args = self.args
 
             for arg in args:
+                # when a word starts with -, it should be negated
+                is_negated = len(arg) > 1 and arg[0] == '-'
+                arg = arg[1:] if is_negated else arg
+
                 if re.match(Filter.ORDINAL_TAG_MATCH, arg):
                     argfilter = Filter.OrdinalTagFilter(arg)
                 elif re.match(Filter.PRIORITY_MATCH, arg):
                     argfilter = Filter.PriorityFilter(arg)
-                elif len(arg) > 1 and arg[0] == '-':
-                    # when a word starts with -, exclude it
-                    argfilter = Filter.GrepFilter(arg[1:])
-                    argfilter = Filter.NegationFilter(argfilter)
                 else:
                     argfilter = Filter.GrepFilter(arg)
 
+                if is_negated:
+                    argfilter = Filter.NegationFilter(argfilter)
+
                 result.append(argfilter)
 
             return result