Merge pull request #2603 from dotty-staging/fix-2591

Fix #2591: Incorrect documentation on general type projections

Author: smarter

docs/docs/reference/dropped/type-projection.md

@@ -6,10 +6,12 @@ title: Dropped: General Type Projection
 Scala so far allowed general type projection `T#A` where `T` is an arbitrary type
 and `A` names a type member of `T`.
 
-Dotty allows this only if `T` is a class type. The change was made because
-unrestricted type projection is [unsound](https://github.com/lampepfl/dotty/issues/1050).
+Dotty disallows this if `T` is an abstract type (class types and type aliases
+are fine). This change was made because unrestricted type projection
+is [unsound](https://github.com/lampepfl/dotty/issues/1050).
 
-The restriction rule out the [type-level encoding of compbinator
- calculus](https://michid.wordpress.com/2010/01/29/scala-type-level-encoding-of-the-ski-calculus/). It also rules out the previous encodings of type
-lambdas using structural types with projection as application.  Type
- lambdas are now [directly supported](../type-lambdas.md) in Dotty.
+This restriction rules out the [type-level encoding of a combinator
+calculus](https://michid.wordpress.com/2010/01/29/scala-type-level-encoding-of-the-ski-calculus/).
+
+To rewrite code using type projections on abstract types, consider using
+path-dependent types or implicit parameters.