profiling panel causes custom middleware to skip "process_exception" call

[ptink]

I detailed my experiments with this here: https://stackoverflow.com/questions/54346767/django-2-0-custom-middleware-process-exception-hook-not-firing?noredirect=1#comment95511527_54346767

Basically I have a custom middleware class that has a process_exception method, but if I also have debug toolbar enabled with the profiling panel added in DEBUG_TOOLBAR_PANELS than the process_exception method in my middleware class will never fire, I can see the traceback for the error occuring but the returned response is a standard django 500 debug page.

Middleware:

class MyMiddleware(MiddlewareMixin):
    def process_exception(self, request, exception):
        print("Exception!")

Activated middleware

DJANGO_MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
    'debug_toolbar.middleware.DebugToolbarMiddleware',
    'path.to.MyMiddleware',
]

Panels:

DEBUG_TOOLBAR_PANELS = (
    'debug_toolbar.panels.versions.VersionsPanel',
    'debug_toolbar.panels.timer.TimerPanel',
    'debug_toolbar.panels.settings.SettingsPanel',
    'debug_toolbar.panels.headers.HeadersPanel',
    'debug_toolbar.panels.request.RequestPanel',
    'debug_toolbar.panels.sql.SQLPanel',
    'debug_toolbar.panels.templates.TemplatesPanel',
    'debug_toolbar.panels.cache.CachePanel',
    'debug_toolbar.panels.signals.SignalsPanel',
    'debug_toolbar.panels.logging.LoggingPanel',
    'debug_toolbar.panels.redirects.RedirectsPanel',
    'debug_toolbar.panels.profiling.ProfilingPanel',  # commenting this out works
)

[ptink]

This duplicates #497 I've just noticed. It would be nice if there was some sort of warning raised because this broke for me in an extremely non-obvious way

[matthiask]

#1132 will make this worse... I wonder what the best way to fix this might be.

It seems to me that this just surfaces the brokenness of the old way of writing Django middleware (process_view / process_response / process_exception)