Handle an Exception without a traceback.

CHANGES.rst

@@ -39,6 +39,9 @@ Unreleased
 -   Fix setting CSP header options on the response. :pr:`2237`
 -   Fix an issue with with the interactive debugger where lines would
     not expand on click for very long tracebacks. :pr:`2239`
+-   The interactive debugger handles displaying an exception that does
+    not have a traceback, such as from ``ProcessPoolExecutor``.
+    :issue:`2217`
 
 
 Version 2.0.1

src/werkzeug/debug/tbtools.py

@@ -357,6 +357,11 @@ def __init__(
             tb = tb.tb_next  # type: ignore
 
     def filter_hidden_frames(self) -> None:
+        # An exception may not have a traceback to filter frames, such
+        # as one re-raised from ProcessPoolExecutor.
+        if not self.frames:
+            return
+
         new_frames: t.List[Frame] = []
         hidden = False
 

tests/test_debug.py

@@ -6,6 +6,7 @@
 
 from werkzeug.debug import console
 from werkzeug.debug import DebuggedApplication
+from werkzeug.debug import get_current_traceback
 from werkzeug.debug import get_machine_id
 from werkzeug.debug.console import HTMLStringO
 from werkzeug.debug.repr import debug_repr
@@ -350,3 +351,12 @@ class MutableException(ValueError):
     except MutableException:
         # previously crashed: `TypeError: unhashable type 'MutableException'`
         Traceback(*sys.exc_info())
+
+
+def test_exception_without_traceback():
+    try:
+        raise Exception("msg1")
+    except Exception as e:
+        # filter_hidden_frames should skip this since it has no traceback
+        e.__context__ = Exception("msg2")
+        get_current_traceback()