Don't crash in exception() if outside of an exception (#533)

CHANGELOG.md

@@ -32,7 +32,8 @@ You can find our backwards-compatibility policy [here](https://github.com/hynek/
 
 - `FilteringBoundLogger.exception()` and  `FilteringBoundLogger.aexception()` now support positional argument formatting like the rest of the methods.
   [#531](https://github.com/hynek/structlog/issues/531)
-
+- `structlog.processors.format_exc_info()` and `structlog.dev.ConsoleRenderer` do not crash anymore when told to format a non-existent exception.
+  [#533](https://github.com/hynek/structlog/issues/533)
 
 
 ## [23.1.0](https://github.com/hynek/structlog/compare/22.3.0...23.1.0) - 2023-04-06

src/structlog/_frames.py

@@ -20,6 +20,9 @@ def _format_exception(exc_info: ExcInfo) -> str:
 
     Shamelessly stolen from stdlib's logging module.
     """
+    if exc_info == (None, None, None):  # type: ignore[comparison-overlap]
+        return "MISSING"
+
     sio = StringIO()
 
     traceback.print_exception(exc_info[0], exc_info[1], exc_info[2], None, sio)

src/structlog/dev.py

@@ -412,7 +412,8 @@ def __call__(  # noqa: PLR0912
         if exc_info:
             exc_info = _figure_out_exc_info(exc_info)
 
-            self._exception_formatter(sio, exc_info)
+            if exc_info != (None, None, None):
+                self._exception_formatter(sio, exc_info)
         elif exc is not None:
             if self._exception_formatter is not plain_traceback:
                 warnings.warn(

tests/test_dev.py

@@ -510,6 +510,19 @@ def test_pickle(self, repr_native_str, force_colors, proto):
             pickle.dumps(r, proto)
         )(None, None, {"event": "foo"})
 
+    def test_no_exception(self):
+        """
+        If there is no exception, don't blow up.
+        """
+        r = dev.ConsoleRenderer(colors=False)
+
+        assert (
+            "hi"
+            == r(
+                None, None, {"event": "hi", "exc_info": (None, None, None)}
+            ).rstrip()
+        )
+
 
 class TestSetExcInfo:
     def test_wrong_name(self):

tests/test_processors.py

@@ -560,7 +560,17 @@ def test_format_exception(self):
         except ValueError as e:
             a = format_exc_info(None, None, {"exc_info": e})
             b = ExceptionRenderer()(None, None, {"exc_info": e})
-            assert a == b
+
+        assert a == b
+
+    @pytest.mark.parametrize("ei", [True, (None, None, None)])
+    def test_no_exception(self, ei):
+        """
+        A missing exception does not blow up.
+        """
+        assert {"exception": "MISSING"} == format_exc_info(
+            None, None, {"exc_info": ei}
+        )
 
 
 class TestUnicodeEncoder: