Merge pull request #1302 from JaSpa/assoctype

[SR-726][AST] Fix access of associated types through class-constrained generic params

Author: slavapestov

lib/AST/Type.cpp

@@ -2239,15 +2239,22 @@ static Type getMemberForBaseType(Module *module,
   // If the parent is an archetype, extract the child archetype with the
   // given name.
   if (auto archetypeParent = substBase->getAs<ArchetypeType>()) {
-    if (!archetypeParent->hasNestedType(name)) {
-      const auto parent = archetypeParent->getParent();
-      if (!parent)
-        return ErrorType::get(module->getASTContext());
-      if (parent->isSelfDerived())
-        return parent->getNestedTypeValue(name);
+    if (archetypeParent->hasNestedType(name))
+      return archetypeParent->getNestedTypeValue(name);
+
+    if (auto parent = archetypeParent->getParent()) {
+      // If the archetype doesn't have the requested type and the parent is not
+      // self derived, error out
+      return parent->isSelfDerived() ? parent->getNestedTypeValue(name)
+                                     : ErrorType::get(module->getASTContext());
+    }
+
+    // If looking for an associated type and the archetype is constrained to a
+    // class, continue to the default associated type lookup
+    if (!assocType || !archetypeParent->getSuperclass()) {
+      // else just error out
+      return ErrorType::get(module->getASTContext());
     }
-    
-    return archetypeParent->getNestedTypeValue(name);
   }
 
   // If the parent is a type variable, retrieve its member type

test/Constraints/associated_types.swift

@@ -4,18 +4,18 @@ protocol Runcible {
   associatedtype Runcee
 }
 
-class Mince { 
-  init() {} 
+class Mince {
+  init() {}
 }
 
 class Spoon : Runcible {
-  init() {} 
+  init() {}
 
   typealias Runcee = Mince
 }
 
 class Owl<T:Runcible> {
-  init() {} 
+  init() {}
 
   func eat(what: T.Runcee, with: T) { }
 }
@@ -31,3 +31,9 @@ func owl2() -> Owl<Spoon> {
 func owl3() {
   Owl<Spoon>().eat(Mince(), with:Spoon())
 }
+
+// "Can't access associated types through class-constrained generic parameters"
+// (https://bugs.swift.org/browse/SR-726)
+func spoon<S: Spoon>(s: S) {
+  let _: S.Runcee? = nil
+}