[tasks] Create different Loop objects for different instances

Fixes Rapptz#2294

Author: Rapptz

discord/ext/tasks/__init__.py

@@ -405,6 +405,21 @@ def change_interval(self, *, seconds=0, minutes=0, hours=0):
         self.hours = hours
         self.minutes = minutes
 
+class _LoopFactory:
+    def __init__(self, func, **kwargs):
+        self.func = func
+        self.name = func.__name__
+        self.kwargs = kwargs
+
+    def __get__(self, obj, objtype):
+        if obj is None:
+            return self
+
+        loop = Loop(self.func, **self.kwargs)
+        loop._injected = obj
+        setattr(obj, self.name, loop)
+        return loop
+
 def loop(*, seconds=0, minutes=0, hours=0, count=None, reconnect=True, loop=None):
     """A decorator that schedules a task in the background for you with
     optional reconnect logic. The decorator returns a :class:`Loop`.
@@ -436,6 +451,33 @@ def loop(*, seconds=0, minutes=0, hours=0, count=None, reconnect=True, loop=None
         The function was not a coroutine.
     """
     def decorator(func):
-        return Loop(func, seconds=seconds, minutes=minutes, hours=hours,
-                          count=count, reconnect=reconnect, loop=loop)
+        defined_within_class = False
+        frames = inspect.stack()
+        # Essentially, to detect whether we're using this decorator a class
+        # context we're walking the stack to see whether it's top level or
+        # within a class level. This code is pretty finicky and hacky but
+        # it's better than the alternative that requires maintaining a list
+        # of IDs. This code does however break if someone assigns a loop
+        # decorator using different ways, such as a dynamically created
+        # class or calling the decorator directly. However such uses should
+        # be niche and thus don't really impede functionality for 99.99% of users
+        for frame in frames[1:]:
+            if frame[3] == '<module>':
+                break
+            if '__module__' in frame[0].f_code.co_names:
+                defined_within_class = True
+                break
+
+        kwargs = {
+            'seconds': seconds,
+            'minutes': minutes,
+            'hours': hours,
+            'count': count,
+            'reconnect': reconnect,
+            'loop': loop
+        }
+
+        if defined_within_class:
+            return _LoopFactory(func, **kwargs)
+        return Loop(func, **kwargs)
     return decorator