fix empty function arguments

Previously, an empty argument was treated as "not an argument at all". Now,
every function call always has at least one argument -- i.e., %foo{} is a
function call whose only argument is "" -- and %foo{,bar} is valid syntax.

beets/util/functemplate.py

@@ -298,13 +298,9 @@ class Parser(object):
         # Try to parse a subexpression in a subparser.
         expressions = []
 
-        while self.pos < len(self.string) and \
-              self.string[self.pos] != GROUP_CLOSE:
+        while self.pos < len(self.string):
             subparser = Parser(self.string[self.pos:])
             subparser.parse_expression()
-            if subparser.pos == 0:
-                # No expression could be parsed.
-                break
 
             # Extract and advance past the parsed expression.
             expressions.append(Expression(subparser.parts))
@@ -316,6 +312,7 @@ class Parser(object):
                 break
 
             # Only other way to terminate an expression is with ,.
+            # Continue to the next argument.
             assert self.string[self.pos] == ARG_SEP
             self.pos += 1
 

test/test_db.py

@@ -398,8 +398,8 @@ class DestinationFunctionTest(unittest.TestCase):
         self._assert_dest('/base/tle')
 
     def test_if_false(self):
-        self._setf(u'%if{,foo}')
-        self._assert_dest('/base/')
+        self._setf(u'x%if{,foo}')
+        self._assert_dest('/base/x')
     
     def test_if_true(self):
         self._setf(u'%if{bar,foo}')

test/test_template.py

@@ -147,10 +147,11 @@ class ParseTest(unittest.TestCase):
         self.assertEqual(list(_normparse(u'foo %bar{bar,bar baz')),
                          [u'foo %bar{bar,bar baz'])
 
-    def test_call_no_args(self):
+    def test_call_empty_arg(self):
         parts = list(_normparse(u'%foo{}'))
         self.assertEqual(len(parts), 1)
-        self._assert_call(parts[0], u"foo", 0)
+        self._assert_call(parts[0], u"foo", 1)
+        self.assertEqual(list(_normexpr(parts[0].args[0])), [])
     
     def test_call_single_arg(self):
         parts = list(_normparse(u'%foo{bar}'))
@@ -192,7 +193,7 @@ class ParseTest(unittest.TestCase):
         self._assert_call(parts[0], u"foo", 2)
         arg_parts = list(_normexpr(parts[0].args[0]))
         self.assertEqual(len(arg_parts), 1)
-        self._assert_call(arg_parts[0], u"bar", 0)
+        self._assert_call(arg_parts[0], u"bar", 1)
         self.assertEqual(list(_normexpr(parts[0].args[1])), [u"baz"])
 
     def test_nested_call_with_argument(self):
@@ -253,6 +254,9 @@ class EvalTest(unittest.TestCase):
     def test_not_subtitute_func_with_no_args(self):
         self.assertEqual(self._eval(u"%lower"), u"%lower")
 
+    def test_function_call_with_empty_arg(self):
+        self.assertEqual(self._eval(u"%len{}"), u"0")
+
 def suite():
     return unittest.TestLoader().loadTestsFromName(__name__)