PEP 544: Specify self-types in protocols (#647)

This is already implemented in mypy in exactly the same way it works for nominal classes (and thus shares most bugs of self-types in nominal classes).

pep-0544.txt

@@ -586,6 +586,30 @@ Continuing the previous example::
   walk(tree)  # OK, 'Tree[float]' is a subtype of 'Traversable'
 
 
+Self-types in protocols
+-----------------------
+
+The self-types in protocols follow the corresponding specification
+[self-types]_ of PEP 484. For example::
+
+  C = TypeVar('C', bound='Copyable')
+  class Copyable(Protocol):
+      def copy(self: C) -> C:
+
+  class One:
+      def copy(self) -> 'One':
+          ...
+
+  T = TypeVar('T', bound='Other')
+  class Other:
+      def copy(self: T) -> T:
+          ...
+
+  c: Copyable
+  c = One()  # OK
+  c = Other()  # Also OK
+
+
 Using Protocols
 ===============
 
@@ -1369,6 +1393,9 @@ References
 .. [elsewhere]
    https://github.com/python/peps/pull/224
 
+.. [self-types]
+   https://www.python.org/dev/peps/pep-0484/#annotating-instance-and-class-methods
+
 
 Copyright
 =========