[TypeCheckAttr] @frozen is valid even when building without enable-library-evolution

[nate-chandler]

Even when building not for library evolution, @frozen is a valid attribute on enums.

Fixes an issue where conformances to Sendable and BitwiseCopyable of @frozen enums are not inferred in targets not built for library evolution such as the embedded stdlib.

rdar://128358780

[nate-chandler]

Alternatively

diff --git a/lib/Sema/TypeCheckAttr.cpp b/lib/Sema/TypeCheckAttr.cpp
index efe408787f6..75d2bfd4e47 100644
--- a/lib/Sema/TypeCheckAttr.cpp
+++ b/lib/Sema/TypeCheckAttr.cpp
@@ -3960,11 +3960,6 @@ void AttributeChecker::visitImplementsAttr(ImplementsAttr *attr) {

 void AttributeChecker::visitFrozenAttr(FrozenAttr *attr) {
   if (auto *ED = dyn_cast<EnumDecl>(D)) {
-    if (!ED->getModuleContext()->isResilient()) {
-      attr->setInvalid();
-      return;
-    }
-
     if (ED->getFormalAccess() < AccessLevel::Package &&
         !ED->getAttrs().hasAttribute<UsableFromInlineAttr>()) {
       diagnoseAndRemoveAttr(attr, diag::enum_frozen_nonpublic, attr);

[DougGregor]

Alternatively

This is the way! The attribute checker shouldn't be marking this attribute invalid.

[slavapestov]

Nice find!

Looking through the git history here, we used to diagnose an error until bf4aaac. Makes sense this shouldn't depend on language mode.

[nate-chandler]

@swift-ci please test

[nate-chandler]

@swift-ci please test source compatibility

[nate-chandler]

@swift-ci Please Test Source Compatibility Debug