Fixes #23643 -- Added chained exception details to debug view.

django/views/debug.py

@@ -479,8 +479,29 @@ class ExceptionReporter(object):
         return lower_bound, pre_context, context_line, post_context
 
     def get_traceback_frames(self):
+        def explicit_or_implicit_cause(exc_value):
+            explicit = getattr(exc_value, '__cause__', None)
+            implicit = getattr(exc_value, '__context__', None)
+            return explicit or implicit
+
+        # Get the exception and all its causes
+        exceptions = []
+        exc_value = self.exc_value
+        while exc_value:
+            exceptions.append(exc_value)
+            exc_value = explicit_or_implicit_cause(exc_value)
+
         frames = []
-        tb = self.tb
+        # No exceptions were supplied to ExceptionReporter
+        if not exceptions:
+            return frames
+
+        # In case there's just one exception (always in Python 2,
+        # sometimes in Python 3), take the traceback from self.tb (Python 2
+        # doesn't have a __traceback__ attribute on Exception)
+        exc_value = exceptions.pop()
+        tb = self.tb if not exceptions else exc_value.__traceback__
+
         while tb is not None:
             # Support for __traceback_hide__ which is used by a few libraries
             # to hide internal frames.
@@ -497,6 +518,8 @@ class ExceptionReporter(object):
             )
             if pre_context_lineno is not None:
                 frames.append({
+                    'exc_cause': explicit_or_implicit_cause(exc_value),
+                    'exc_cause_explicit': getattr(exc_value, '__cause__', True),
                     'tb': tb,
                     'type': 'django' if module_name.startswith('django.') else 'user',
                     'filename': filename,
@@ -509,7 +532,14 @@ class ExceptionReporter(object):
                     'post_context': post_context,
                     'pre_context_lineno': pre_context_lineno + 1,
                 })
-            tb = tb.tb_next
+
+            # If the traceback for current exception is consumed, try the
+            # other exception.
+            if not tb.tb_next and exceptions:
+                exc_value = exceptions.pop()
+                tb = exc_value.__traceback__
+            else:
+                tb = tb.tb_next
 
         return frames
 
@@ -838,6 +868,15 @@ TECHNICAL_500_TEMPLATE = ("""
   <div id="browserTraceback">
     <ul class="traceback">
       {% for frame in frames %}
+        {% ifchanged frame.exc_cause %}{% if frame.exc_cause %}
+          <li><h3>
+          {% if frame.exc_cause_explicit %}
+            The above exception ({{ frame.exc_cause }}) was the direct cause of the following exception:
+          {% else %}
+            During handling of the above exception ({{ frame.exc_cause }}), another exception occurred:
+          {% endif %}
+        </h3></li>
+        {% endif %}{% endifchanged %}
         <li class="frame {{ frame.type }}">
           <code>{{ frame.filename|escape }}</code> in <code>{{ frame.function|escape }}</code>
 
@@ -1123,7 +1162,17 @@ In template {{ template_info.name }}, error at line {{ template_info.line }}
    {{ source_line.0 }} : {{ source_line.1 }}
    {% endifequal %}{% endfor %}{% endif %}{% if frames %}
 Traceback:
-{% for frame in frames %}File "{{ frame.filename }}" in {{ frame.function }}
+{% for frame in frames %}
+{% ifchanged frame.exc_cause %}
+  {% if frame.exc_cause %}
+    {% if frame.exc_cause_explicit %}
+      The above exception ({{ frame.exc_cause }}) was the direct cause of the following exception:
+    {% else %}
+      During handling of the above exception ({{ frame.exc_cause }}), another exception occurred:
+    {% endif %}
+  {% endif %}
+{% endifchanged %}
+File "{{ frame.filename }}" in {{ frame.function }}
 {% if frame.context_line %}  {{ frame.lineno }}. {{ frame.context_line }}{% endif %}
 {% endfor %}
 {% if exception_type %}Exception Type: {{ exception_type }}{% if request %} at {{ request.path_info }}{% endif %}