Closes #1921

CHANGELOG.md

@@ -26,6 +26,7 @@ Semantic versioning in our case means:
 - Fixes `ReassigningVariableToItselfViolation` to not report on `x = (x,)` #1807
 - Fixes `ReassigningVariableToItselfViolation` to extract variables
   from unary operators #1874
+- Fixes that `f'{some:,}'` was considered too complex #1921
 
 ### Misc
 

tests/test_visitors/test_ast/test_builtins/test_strings/test_formatted_string.py

@@ -53,6 +53,9 @@
 f_double_call_arg = "f'{foo()(arg)}'"
 f_single_chained_functions = "f'{f1().f2()}'"
 
+# regression 1921
+f_string_comma_format = 'f"Count={count:,}"'
+
 
 @pytest.mark.parametrize('code', [
     regular_string,
@@ -132,6 +135,7 @@ def test_complex_f_string(assert_errors, parse_ast_tree, code, default_options):
     f_true_index,
     f_none_index,
     f_byte_index,
+    f_string_comma_format,
 ])
 def test_simple_f_string(assert_errors, parse_ast_tree, code, default_options):
     """Testing that non complex ``f`` strings are allowed."""

wemake_python_styleguide/visitors/ast/builtins.py

@@ -186,10 +186,12 @@ def visit_JoinedStr(self, node: ast.JoinedStr) -> None:
             TooComplexFormattedStringViolation
 
         """
-        self._check_complex_formatted_string(node)
-
-        # We don't allow `f` strings by default:
-        self.add_violation(consistency.FormattedStringViolation(node))
+        if not isinstance(nodes.get_parent(node), ast.FormattedValue):
+            # We don't allow `f` strings by default,
+            # But, we need this condition to make sure that this
+            # is not a part of complex string format like `f"Count={count:,}"`:
+            self._check_complex_formatted_string(node)
+            self.add_violation(consistency.FormattedStringViolation(node))
         self.generic_visit(node)
 
     def _check_complex_formatted_string(self, node: ast.JoinedStr) -> None:
@@ -261,8 +263,7 @@ def _is_valid_chain_structure(self, chained_parts: List[ast.AST]) -> bool:
                 isinstance(part, self._single_use_types)
                 for part in chained_parts
             ) == 1
-        # All chaining with fewer elements is fine!
-        return True
+        return True  # All chaining with fewer elements is fine!
 
 
 @final