[Concurrency] Diagnose redundant (unsafe) for a static constant Sendable property of an actor.

Author: simanerush

include/swift/AST/DiagnosticsSema.def

@@ -5690,6 +5690,10 @@ WARNING(nonisolated_unsafe_sendable_struct,none,
      "'nonisolated(unsafe)' is unnecessary for a constant with 'Sendable' type "
      "%0, consider removing it",
      (Type))
+WARNING(unsafe_sendable_actor,none,
+     "'(unsafe)' is unnecessary for a constant actor property with 'Sendable' "
+     "type  %0, consider removing it",
+     (Type))
 ERROR(nonisolated_non_sendable,none,
       "'nonisolated' can not be applied to variable with non-'Sendable' "
       "type %0",

lib/Sema/TypeCheckAttr.cpp

@@ -6917,6 +6917,17 @@ void AttributeChecker::visitNonisolatedAttr(NonisolatedAttr *attr) {
           if (isa<StructDecl>(nominal))
             diagnoseAndRemoveAttr(
                 attr, diag::nonisolated_unsafe_sendable_struct, type);
+
+          // '(unsafe)' is redundant for static constant 'Sendable' actor
+          // properties.
+          // TODO: Should this apply to only public actors?
+          if (nominal->isActor()) {
+            // Get the location where '(unsafe)' starts.
+            SourceLoc unsafeStart = Lexer::getLocForEndOfToken(
+                Ctx.SourceMgr, attr->getRange().Start);
+            diagnose(unsafeStart, diag::unsafe_sendable_actor, type)
+                .fixItRemoveChars(unsafeStart, attr->getRange().End);
+          }
         }
 
         // 'nonisolated' is redundant for the stored properties of a struct.

test/Concurrency/global_variables.swift

@@ -54,6 +54,11 @@ struct TestStatics {
   // expected-note@-1{{isolate 'wrapped' to a global actor, or convert it to a 'let' constant and conform it to 'Sendable'}}
 }
 
+actor TestPublicActor {
+  static nonisolated(unsafe) let immutableNonisolatedUnsafeSendable = TestSendable()
+  // expected-warning@-1 {{'(unsafe)' is unnecessary for a constant actor property with 'Sendable' type  'TestSendable', consider removing it}}
+}
+
 @TestGlobalActor
 func f() {
   print(TestStatics.immutableExplicitSendable)