[Scope map] Handle unqualified name lookup into protocols and protocol extensions properly.

We need to use the 'Self' type, not the nominal type itself.

Author: DougGregor

lib/AST/NameLookup.cpp

@@ -598,7 +598,12 @@ UnqualifiedLookup::UnqualifiedLookup(DeclName Name, DeclContext *DC,
 
         // Dig out the type we're looking into.
         // FIXME: We shouldn't need to compute a type to perform this lookup.
-        auto lookupType = dc->getDeclaredTypeInContext();
+        Type lookupType;
+
+        if (dc->getAsProtocolOrProtocolExtensionContext())
+          lookupType = dc->getSelfTypeInContext();
+        else
+          lookupType = dc->getDeclaredTypeInContext();
         if (!lookupType || lookupType->is<ErrorType>()) continue;
 
         // If we're performing a static lookup, use the metatype.

test/NameBinding/scope_map_lookup.swift

@@ -52,3 +52,28 @@ class LazyProperties {
 
   lazy var prop5: Int = { self.value + 1 }()
 }
+
+// Protocol extensions.
+// Extending via a superclass constraint.
+class Superclass {
+  func foo() { }
+  static func bar() { }
+
+  typealias Foo = Int
+}
+
+protocol PConstrained4 { }
+
+extension PConstrained4 where Self : Superclass {
+  final func testFoo() -> Foo {
+    foo()
+    self.foo()
+
+    return Foo(5)
+  }
+
+  final static func testBar() {
+    bar()
+    self.bar()
+  }
+}