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/functional/l/logging/logging_unsupported_format.py

@@ -0,0 +1,23 @@
+"""Tests for logging-unsupported-format (issue #10752)
+
+According to Python logging documentation, no formatting is performed
+when no arguments are supplied. This test verifies that unsupported
+format characters are only reported when arguments are provided.
+"""
+
+import logging
+
+# These should NOT trigger warnings (no args = no formatting)
+logging.error("%test")
+logging.warning("%badformat")
+logging.info("%z - invalid specifier")
+logging.debug("%q %k %z - multiple invalid")
+
+# These SHOULD trigger warnings (args provided = formatting attempted)
+logging.error("%test", 123)  # [logging-unsupported-format]
+logging.warning("%bad", "arg")  # [logging-unsupported-format]
+logging.info("Value: %s, Invalid: %z", "test", "val")  # [logging-unsupported-format]
+
+# Valid format strings should work fine
+logging.info("User %s logged in", "john")
+logging.debug("Count: %d", 42)

tests/functional/l/logging/logging_unsupported_format.txt

@@ -0,0 +1,3 @@
+logging-unsupported-format:17:0:17:27::Unsupported logging format character 't' (0x74) at index 1:UNDEFINED
+logging-unsupported-format:18:0:18:30::Unsupported logging format character 'b' (0x62) at index 1:UNDEFINED
+logging-unsupported-format:19:0:19:53::Unsupported logging format character 'z' (0x7a) at index 21:UNDEFINED