fix: Use a noop with the same signature as the real one for make_filtering_bound_logger

CHANGELOG.rst

@@ -26,6 +26,9 @@ Backward-incompatible changes:
 
 - Python 3.6 is not supported anymore.
 - Pickling is now only possible with protocol version 3 and newer.
+- ``structlog.make_filtering_bound_logger()`` now returns a method with the same signature for all log levels, whether they are active or not.
+  This ensures that invalid calls to inactive log levels are caught immediately and don't explode once the log level changes.
+  `#401 <https://github.com/hynek/structlog/pull/401>`_
 
 
 Deprecations:

src/structlog/_log_levels.py

@@ -67,7 +67,7 @@ def add_log_level(
     return event_dict
 
 
-def _nop(*args: Any, **kw: Any) -> Any:
+def _nop(self: Any, event: str, **kw: Any) -> Any:
     return None
 
 

tests/test_log_levels.py

@@ -34,12 +34,34 @@ def test_exact_level(self, bl, cl):
 
     def test_one_below(self, bl, cl):
         """
-        if log level is exactly the min_level, log.
+        if log level is below the min_level, don't log.
         """
         bl.debug("nope")
 
         assert [] == cl.calls
 
+    def test_filter_bound_below_missing_event_string(self, bl, cl):
+        """
+        Missing event arg causes exception below min_level.
+        """
+        with pytest.raises(TypeError) as exc_info:
+            bl.debug(missing="event string!")
+        assert exc_info.type is TypeError
+
+        message = "missing 1 required positional argument: 'event'"
+        assert message in exc_info.value.args[0]
+
+    def test_filter_bound_exact_missing_event_string(self, bl, cl):
+        """
+        Missing event arg causes exception even at min_level.
+        """
+        with pytest.raises(TypeError) as exc_info:
+            bl.info(missing="event string!")
+        assert exc_info.type is TypeError
+
+        message = "missing 1 required positional argument: 'event'"
+        assert message in exc_info.value.args[0]
+
     def test_exception(self, bl, cl):
         """
         exception ensures that exc_info is set to True, unless it's already