fix unsupported logging format check

doc/whatsnew/fragments/10752.false_positive

@@ -0,0 +1,5 @@
+Fixed false positive for ``logging-unsupported-format`` when no arguments are provided to logging functions.
+
+According to Python's logging documentation, no formatting is performed when no arguments are supplied, so strings like ``logging.error("%test")`` are valid.
+
+Closes #10752

pylint/checkers/logging.py

@@ -355,12 +355,16 @@ def _check_format_string(self, node: nodes.Call, format_arg: Literal[0, 1]) -> N
                         keyword_args_cnt + implicit_pos_args + explicit_pos_args
                     )
             except utils.UnsupportedFormatCharacter as ex:
-                char = format_string[ex.index]
-                self.add_message(
-                    "logging-unsupported-format",
-                    node=node,
-                    args=(char, ord(char), ex.index),
-                )
+                if num_args > 0:
+                    # Only report unsupported format characters if arguments are provided
+                    # When no arguments are supplied, no formatting is performed
+                    # https://docs.python.org/3/library/logging.html#logging.Logger.debug
+                    char = format_string[ex.index]
+                    self.add_message(
+                        "logging-unsupported-format",
+                        node=node,
+                        args=(char, ord(char), ex.index),
+                    )
                 return
             except utils.IncompleteFormatString:
                 self.add_message("logging-format-truncated", node=node)

tests/checkers/unittest_logging.py

@@ -0,0 +1,112 @@
+# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+# For details: https://github.com/pylint-dev/pylint/blob/main/LICENSE
+# Copyright (c) https://github.com/pylint-dev/pylint/blob/main/CONTRIBUTORS.txt
+
+"""Tests for the logging checker."""
+
+from __future__ import annotations
+
+import astroid
+from astroid import nodes
+
+from pylint.checkers.logging import LoggingChecker
+from pylint.testutils import CheckerTestCase
+
+
+class TestLoggingChecker(CheckerTestCase):
+    """Tests for LoggingChecker."""
+
+    CHECKER_CLASS = LoggingChecker
+
+    def _check_code(self, code: str) -> None:
+        """Helper to properly check a code snippet with the logging checker."""
+        module = astroid.parse(code)
+        self.checker.visit_module(module)
+        # Walk the entire AST tree
+        for node in module.nodes_of_class((nodes.Import, nodes.ImportFrom)):
+            if isinstance(node, nodes.Import):
+                self.checker.visit_import(node)
+            else:
+                self.checker.visit_importfrom(node)
+        for node in module.nodes_of_class(nodes.Call):
+            self.checker.visit_call(node)
+
+    def test_logging_unsupported_format_without_args(self) -> None:
+        """Test that unsupported format chars are not reported without args.
+
+        According to Python docs, no formatting is performed when no args are supplied.
+        This test verifies the fix for issue #10752.
+        """
+        with self.assertNoMessages():
+            self._check_code(
+                """
+import logging
+logging.warning("%badformat")
+            """
+            )
+
+    def test_logging_original_issue_10752(self) -> None:
+        """Test the exact case from issue #10752."""
+        with self.assertNoMessages():
+            self._check_code(
+                """
+import logging
+logging.error("%test")
+            """
+            )
+
+    def test_logging_invalid_format_specifier_without_args(self) -> None:
+        """Test invalid format specifiers without args don't trigger unsupported-format."""
+        with self.assertNoMessages():
+            self._check_code(
+                """
+import logging
+logging.info("%z - invalid but no args so no formatting")
+            """
+            )
+
+    def test_logging_multiple_invalid_format_without_args(self) -> None:
+        """Test multiple invalid format chars without args."""
+        with self.assertNoMessages():
+            self._check_code(
+                """
+import logging
+logging.warning("%q %z %k - all invalid but no args")
+            """
+            )
+
+    def test_logging_valid_format_with_args(self) -> None:
+        """Test that valid format strings with args don't trigger warnings."""
+        with self.assertNoMessages():
+            self._check_code(
+                """
+import logging
+logging.info("User %s logged in", "john")
+            """
+            )
+
+    def test_logging_unsupported_format_with_args_still_caught(self) -> None:
+        """Test that unsupported format chars ARE reported when args are provided."""
+        self._check_code(
+            """
+import logging
+logging.error("%test", 123)
+        """
+        )
+        # Check that at least one message was added
+        messages = self.linter.release_messages()
+        assert len(messages) > 0
+        assert any(msg.msg_id == "logging-unsupported-format" for msg in messages)
+
+    def test_logging_mixed_invalid_format_with_args_still_caught(self) -> None:
+        """Test that invalid format chars are still caught when args provided."""
+        self._check_code(
+            """
+import logging
+logging.error("Value: %s, Invalid: %z", "test", "value")
+        """
+        )
+        # Check that unsupported-format message was added
+        messages = self.linter.release_messages()
+        assert len(messages) > 0
+        assert any(msg.msg_id == "logging-unsupported-format" for msg in messages)