[formatter] allow dots etc in '…' literals (#5539)

don't parse fields starting with '

this disables the ability to directly apply […] to '…' literals,
but that's not really useful anyway and can still be done with _lit

gallery_dl/formatter.py

@@ -243,13 +243,12 @@ class TemplateFStringFormatter(FStringFormatter):
 
 
 def parse_field_name(field_name):
+    if field_name[0] == "'":
+        return "_lit", (operator.itemgetter(field_name[1:-1]),)
+
     first, rest = _string.formatter_field_name_split(field_name)
     funcs = []
 
-    if first[0] == "'":
-        funcs.append(operator.itemgetter(first[1:-1]))
-        first = "_lit"
-
     for is_attr, key in rest:
         if is_attr:
             func = operator.attrgetter

test/test_formatter.py

@@ -336,14 +336,14 @@ class TestFormatter(unittest.TestCase):
     def test_literals(self):
         value = "foo"
 
-        self._run_test("{'foo'}"       , value)
-        self._run_test("{'foo'!u}"     , value.upper())
-        self._run_test("{'f00':R0/o/}" , value)
-        self._run_test("{'foobar'[:3]}", value)
-        self._run_test("{z|'foo'}"     , value)
-        self._run_test("{z|''|'foo'}"  , value)
-        self._run_test("{z|''}"        , "")
-        self._run_test("{''|''}"       , "")
+        self._run_test("{'foo'}"      , value)
+        self._run_test("{'foo'!u}"    , value.upper())
+        self._run_test("{'f00':R0/o/}", value)
+
+        self._run_test("{z|'foo'}"      , value)
+        self._run_test("{z|''|'foo'}"   , value)
+        self._run_test("{z|'foo'!u}"    , value.upper())
+        self._run_test("{z|'f00':R0/o/}", value)
 
         self._run_test("{_lit[foo]}"       , value)
         self._run_test("{_lit[foo]!u}"     , value.upper())
@@ -351,6 +351,17 @@ class TestFormatter(unittest.TestCase):
         self._run_test("{_lit[foobar][:3]}", value)
         self._run_test("{z|_lit[foo]}"     , value)
 
+        # empty (#4492)
+        self._run_test("{z|''}" , "")
+        self._run_test("{''|''}", "")
+
+        # special characters (dots, brackets, singlee quotes) (#5539)
+        self._run_test("{'f.o.o'}"    , "f.o.o")
+        self._run_test("{_lit[f.o.o]}", "f.o.o")
+        self._run_test("{_lit[f'o'o]}", "f'o'o")
+        self._run_test("{'f.[].[]'}"  , "f.[].[]")
+        self._run_test("{z|'f.[].[]'}", "f.[].[]")
+
     def test_template(self):
         with tempfile.TemporaryDirectory() as tmpdirname:
             path1 = os.path.join(tmpdirname, "tpl1")