Verify behavior of Swift 3 and Swift 4 final protocol extension behavior

Author: Brian King

test/Compatibility/attr_final_protocol_extension.swift

@@ -0,0 +1,8 @@
+// RUN: %target-typecheck-verify-swift -swift-version 3
+// Generate a swift 3 compatible warning if final is specified in an extension
+
+protocol P {}
+
+extension P {
+  final func inExtension() {} // expected-warning{{functions in a protocol extension do not need to be marked with 'final'}} {{3-9=}}
+}

test/attr/attr_final_protocol_extension.swift

@@ -0,0 +1,7 @@
+// RUN: %target-typecheck-verify-swift -swift-version 4
+
+protocol P {}
+
+extension P {
+  final func inExtension() {} // expected-error {{only classes and class members may be marked with 'final'}} {{3-9=}}
+}