After #3515 is merged there are plenty of unnecessary re_path's left, but figuring out if simplification is possible is trickier.

Here are some known problems:

• regexpes that do not end with $
• Year, month, and day-number could get their own patterns
• Ip-address could maybe get its own pattern
• Ditto hostnames
• There are several regexpes that could probably be covered by <path: or <str: or <slug:
• No doubt many that take in re_path(r'(?P<id>.+) could actually be replaced with path('<int:id>, and WAT about re_path(r'^x/(?P<id>.*) when re_path(r'^x/$ does not exist?
• Some regexpes end with /?. APPEND_SLASH is implicitly True and django.middleware.common.CommonMiddleware is in use so this is probably redundant

When all the easy pickings have landed, https://regex101.com/ is useful to compare regexpes in order to simplify them. For instance, re_path(r'^(?P<id>\d+)$' and re_path(r'^(?P<id>[\d]+)$' are equivalent to path('<int:id>)' but `re_path(r'^(?P(\d+))$' is not and it is necessary to check what the view does in order to ascertain if the simplification is possible.

Originally posted by @hmpf in #3515