Sema: Diagnose @_spi on elements of @frozen enums.

rdar://72873771

Author: tshortli

include/swift/AST/DiagnosticsSema.def

@@ -1970,6 +1970,9 @@ ERROR(spi_attribute_on_protocol_requirement,none,
 ERROR(spi_attribute_on_frozen_stored_properties,none,
       "stored property %0 cannot be declared '@_spi' in a '@frozen' struct",
       (DeclName))
+ERROR(spi_attribute_on_frozen_enum_case,none,
+      "%0 %1 cannot be declared '@_spi' in a '@frozen' enum",
+      (DescriptiveDeclKind, DeclName))
 WARNING(spi_attribute_on_import_of_public_module,none,
         "'@_spi' import of %0 will not include any SPI symbols; "
         "%0 was built from the public interface at %1",

lib/Sema/TypeCheckAttr.cpp

@@ -1150,6 +1150,17 @@ void AttributeChecker::visitSPIAccessControlAttr(SPIAccessControlAttr *attr) {
         }
       }
     }
+
+    // Forbid enum elements marked SPI in frozen types.
+    if (auto elt = dyn_cast<EnumElementDecl>(VD)) {
+      if (auto ED = dyn_cast<EnumDecl>(D->getDeclContext())) {
+        if (ED->getAttrs().hasAttribute<FrozenAttr>(/*allowInvalid*/ true) &&
+            !ED->isSPI()) {
+          diagnoseAndRemoveAttr(attr, diag::spi_attribute_on_frozen_enum_case,
+                                VD->getDescriptiveKind(), VD->getName());
+        }
+      }
+    }
   }
 
   if (auto ID = dyn_cast<ImportDecl>(D)) {

test/SPI/resilience.swift

@@ -14,7 +14,7 @@ public class Bar {
   public init() {}
 }
 
-public struct Resilient {
+public struct ResilientStructSPIMembers {
   public init() {}
 
   @_spi(Foo) public func method(_: Bar) {}
@@ -28,7 +28,7 @@ public struct Resilient {
   @_spi(Foo) @Wrapper public var wrappedProperty2 = Bar()
 }
 
-@frozen public struct Good {
+@frozen public struct FrozenStructSPIMembers {
   public init() {}
 
   @_spi(Foo) public func method(_: Bar) {}
@@ -55,7 +55,7 @@ public struct Resilient {
   // expected-error@-1 {{stored property 'wrappedProperty2' cannot be declared '@_spi' in a '@frozen' struct}}
 }
 
-@frozen public struct Bad {
+@frozen public struct FrozenStructPublicMembers {
   public init() {}
 
   public func method(_: Bar) {} // expected-error {{cannot use class 'Bar' here; it is SPI}}
@@ -83,7 +83,7 @@ public struct Resilient {
   // expected-error@-3 {{initializer 'init()' cannot be used in a property initializer in a '@frozen' type because it is SPI}}
 }
 
-@frozen public struct BadPrivate {
+@frozen public struct FrozenStructPrivateMembers {
   private init() {}
 
   private func method(_: Bar) {}
@@ -110,3 +110,24 @@ public struct Resilient {
   // expected-error@-2 {{class 'Bar' cannot be used in a property initializer in a '@frozen' type because it is SPI}}
   // expected-error@-3 {{initializer 'init()' cannot be used in a property initializer in a '@frozen' type because it is SPI}}
 }
+
+public enum ResilientEnum {
+  @_spi(S)
+  case okSpiCase
+
+  @_spi(S)
+  case okSpiCaseWithPayload(_: Int)
+}
+
+@frozen
+public enum FrozenEnum {
+  case okCase
+
+  @_spi(S) // expected-error {{enum case 'spiCase' cannot be declared '@_spi' in a '@frozen' enum}}
+  case spiCase
+
+  case okCaseWithPayload(_: Int)
+
+  @_spi(S) // expected-error {{enum case 'spiCaseWithPayload' cannot be declared '@_spi' in a '@frozen' enum}}
+  case spiCaseWithPayload(_: Int)
+}