fix(functemplate): empty ${} inside a call argument truncates the argument list

beets/util/functemplate.py

@@ -380,8 +380,13 @@ def parse_symbol(self):
             # A symbol like ${this}.
             self.pos += 1  # Skip opening.
             closer = self.string.find(GROUP_CLOSE, self.pos)
-            if closer == -1 or closer == self.pos:
-                # No closing brace found or identifier is empty.
+            if closer == -1:
+                # No closing brace found.
+                self.parts.append(self.string[start_pos : self.pos])
+            elif closer == self.pos:
+                # Empty identifier: consume through the closing brace so it
+                # cannot be mistaken for an enclosing call's terminator.
+                self.pos = closer + 1
                 self.parts.append(self.string[start_pos : self.pos])
             else:
                 # Closer found.

docs/changelog.rst

@@ -95,6 +95,9 @@ Bug fixes
   valid date/time string" error instead of crashing with an uncaught
   ``KeyError``. A ``|`` was being accepted as a relative-date unit due to a
   regular expression character-class typo.
+- Path formats: an empty ``${}`` inside a function call argument no longer
+  truncates the argument list and leaks the rest of the template as literal
+  text.
 
 ..
     For plugin developers

test/util/test_functemplate.py

@@ -115,6 +115,19 @@ def test_unclosed_braces_symbol(self):
     def test_empty_braces_symbol(self):
         assert list(_normparse("a ${} b")) == ["a ${} b"]
 
+    def test_empty_braces_symbol_inside_call_arg(self):
+        parts = list(_normparse("%foo{a${}b}"))
+        assert len(parts) == 1
+        self._assert_call(parts[0], "foo", 1)
+        assert list(_normexpr(parts[0].args[0])) == ["a${}b"]
+
+    def test_empty_braces_symbol_inside_call_arg_list(self):
+        parts = list(_normparse("%foo{a${}b,baz}"))
+        assert len(parts) == 1
+        self._assert_call(parts[0], "foo", 2)
+        assert list(_normexpr(parts[0].args[0])) == ["a${}b"]
+        assert list(_normexpr(parts[0].args[1])) == ["baz"]
+
     def test_call_without_args_at_end(self):
         assert list(_normparse("foo %bar")) == ["foo %bar"]