Allow final on dynamic members

Dynamic is about dynamically replacing a method implementiation not
overriding.

rdar://49535048

Author: aschwaighofer

lib/Sema/TypeCheckAttr.cpp

@@ -324,7 +324,10 @@ void AttributeEarlyChecker::visitMutationAttr(DeclAttribute *attr) {
 
 void AttributeEarlyChecker::visitDynamicAttr(DynamicAttr *attr) {
   // Members cannot be both dynamic and final.
-  if (D->getAttrs().hasAttribute<FinalAttr>())
+  // We do allow dynamic final members for dynamic replacement in
+  // swift-version 5.
+  if (D->getAttrs().hasAttribute<FinalAttr>() &&
+      !D->getASTContext().LangOpts.isSwiftVersionAtLeast(5))
     diagnoseAndRemoveAttr(attr, diag::dynamic_with_final);
 
   // Members cannot be both dynamic and @nonobjc.
@@ -2590,8 +2593,12 @@ void TypeChecker::addImplicitDynamicAttribute(Decl *D) {
       isa<AccessorDecl>(D))
     return;
 
-  if (D->getAttrs().hasAttribute<FinalAttr>() ||
-      D->getAttrs().hasAttribute<NonObjCAttr>() ||
+  // Don't add implicit dynamic to final functions before swift-version 5.
+  if (D->getAttrs().hasAttribute<FinalAttr>() &&
+      !D->getASTContext().LangOpts.isSwiftVersionAtLeast(5))
+    return;
+
+  if (D->getAttrs().hasAttribute<NonObjCAttr>() ||
       D->getAttrs().hasAttribute<TransparentAttr>() ||
       D->getAttrs().hasAttribute<InlinableAttr>())
     return;

test/Interpreter/Inputs/dynamic_replacement_module.swift

@@ -17,6 +17,9 @@ public class PublicClass {
   public dynamic func function() -> String {
     return "public_class_func"
   }
+  public dynamic final func finalFunction() -> String {
+    return "public_class_final_func"
+  }
   public dynamic func genericFunction<T>(_ t: T.Type) -> String {
     return "public_class_generic_func"
   }
@@ -84,6 +87,11 @@ public class PublicClass {
   public func function() -> String {
     return "public_class_func"
   }
+
+  public final func finalFunction() -> String {
+    return "public_class_final_func"
+  }
+
   public func genericFunction<T>(_ t: T.Type) -> String {
     return "public_class_generic_func"
   }
@@ -163,6 +171,10 @@ extension PublicClass {
   public func replacement_function() -> String {
     return "replacement of " + function()
   }
+  @_dynamicReplacement(for: finalFunction())
+  public func replacement_finalFunction() -> String {
+    return "replacement of " + finalFunction()
+  }
   @_dynamicReplacement(for: genericFunction(_:))
   public func replacement_genericFunction<T>(_ t: T.Type) -> String {
     return "replacement of " + genericFunction(t)

test/Interpreter/dynamic_replacement.swift

@@ -84,6 +84,8 @@ func checkExpectedResults(forOriginalLibrary useOrig: Bool) {
 
  expectTrue(PublicClass().function() ==
             expectedResult(useOrig, "public_class_func"))
+ expectTrue(PublicClass().finalFunction() ==
+            expectedResult(useOrig, "public_class_final_func"))
  expectTrue(PublicClass().genericFunction(Int.self) ==
             expectedResult(useOrig, "public_class_generic_func"))
 

test/attr/Inputs/dynamicReplacementC.swift

@@ -11,4 +11,5 @@ public extension TheReplaceables {
 public class K {
   public init(i: Int) {}
   public convenience init(c : Int) { self.init(i : c) }
+  public final func finalFunction() {}
 }

test/attr/dynamicReplacement.swift

@@ -45,6 +45,9 @@ extension K {
 
   @_dynamicReplacement(for: init(c:)) // expected-error{{replaced constructor 'init(c:)' is marked as convenience}})
   init(rc: Int) { }
+
+  @_dynamicReplacement(for:finalFunction())
+  func replacement_finalFunction() {}
 }
 
 extension undeclared { // expected-error{{use of undeclared type 'undeclared'}}