SE-0302: Limit ConcurrentValue on classes to final classes

Author: DougGregor

include/swift/AST/DiagnosticsSema.def

@@ -4360,11 +4360,11 @@ WARNING(concurrent_value_outside_source_file_warn,none,
       "conformance to 'ConcurrentValue' must occur in the same source file as "
       "%0 %1; use 'UnsafeConcurrentValue' for retroactive conformance",
       (DescriptiveDeclKind, DeclName))
-ERROR(concurrent_value_open_class,none,
-      "open class %0 cannot conform to `ConcurrentValue`; "
+ERROR(concurrent_value_nonfinal_class,none,
+      "non-final class %0 cannot conform to `ConcurrentValue`; "
       "use `UnsafeConcurrentValue`", (DeclName))
-WARNING(concurrent_value_open_class_warn,none,
-      "open class %0 cannot conform to `ConcurrentValue`; "
+WARNING(concurrent_value_nonfinal_class_warn,none,
+      "non-final class %0 cannot conform to `ConcurrentValue`; "
       "use `UnsafeConcurrentValue`", (DeclName))
 ERROR(concurrent_value_inherit,none,
       "`ConcurrentValue` class %1 cannot inherit from another class"

lib/Sema/TypeCheckConcurrency.cpp

@@ -2483,11 +2483,11 @@ bool swift::checkConcurrentValueConformance(
   }
 
   if (classDecl) {
-    // An open class cannot conform to `ConcurrentValue`.
-    if (classDecl->getFormalAccess() == AccessLevel::Open) {
+    // An non-final class cannot conform to `ConcurrentValue`.
+    if (!classDecl->isFinal()) {
       classDecl->diagnose(
-          asWarning ? diag::concurrent_value_open_class_warn
-                    : diag::concurrent_value_open_class,
+          asWarning ? diag::concurrent_value_nonfinal_class_warn
+                    : diag::concurrent_value_nonfinal_class,
           classDecl->getName());
 
       if (!asWarning)

test/Concurrency/concurrent_value_checking.swift

@@ -215,21 +215,19 @@ enum E2<T> {
 
 extension E2: ConcurrentValue where T: ConcurrentValue { }
 
-class C1: ConcurrentValue {
+final class C1: ConcurrentValue {
   let nc: NotConcurrent? = nil // expected-error{{stored property 'nc' of 'ConcurrentValue'-conforming class 'C1' has non-concurrent-value type 'NotConcurrent?'}}
   var x: Int = 0 // expected-error{{stored property 'x' of 'ConcurrentValue'-conforming class 'C1' is mutable}}
   let i: Int = 0
 }
 
-class C2: ConcurrentValue {
+final class C2: ConcurrentValue {
   let x: Int = 0
 }
 
-class C3: C2 {
-  var y: Int = 0 // expected-error{{stored property 'y' of 'ConcurrentValue'-conforming class 'C3' is mutable}}
-}
+class C3 { }
 
-class C4: C2, UnsafeConcurrentValue {
+class C4: C3, UnsafeConcurrentValue {
   var y: Int = 0 // okay
 }
 
@@ -241,17 +239,9 @@ class C6: C5 {
   var y: Int = 0 // still okay, it's unsafe
 }
 
-class C7<T>: ConcurrentValue { }
-
-class C8: C7<Int> { } // okay
-
-open class C9: ConcurrentValue { } // expected-error{{open class 'C9' cannot conform to `ConcurrentValue`; use `UnsafeConcurrentValue`}}
+final class C7<T>: ConcurrentValue { }
 
-public class C10: ConcurrentValue { }
-// expected-note@-1{{superclass is declared here}}
-open class C11: C10 { }
-// expected-error@-1{{superclass 'C10' of open class must be open}}
-// expected-error@-2{{open class 'C11' cannot conform to `ConcurrentValue`; use `UnsafeConcurrentValue`}}
+class C9: ConcurrentValue { } // expected-error{{non-final class 'C9' cannot conform to `ConcurrentValue`; use `UnsafeConcurrentValue`}}
 
 // ----------------------------------------------------------------------
 // UnsafeConcurrentValue disabling checking

test/Concurrency/concurrent_value_checking_objc.swift

@@ -5,17 +5,17 @@
 
 import Foundation
 
-class A: NSObject, ConcurrentValue {
+final class A: NSObject, ConcurrentValue {
   let x: Int = 5
 }
 
-class B: NSObject, ConcurrentValue {
+final class B: NSObject, ConcurrentValue {
   var x: Int = 5 // expected-error{{stored property 'x' of 'ConcurrentValue'-conforming class 'B' is mutable}}
 }
 
 class C { }
 
-class D: NSObject, ConcurrentValue {
+final class D: NSObject, ConcurrentValue {
   let c: C = C() // expected-error{{stored property 'c' of 'ConcurrentValue'-conforming class 'D' has non-concurrent-value type 'C'}}
 }