Revert "[BitwiseCopyable] Don't derive on @unchecked field"

This reverts commit d9e1755.

Author: nate-chandler

lib/Sema/TypeCheckBitwise.cpp

@@ -106,7 +106,6 @@ class BitwiseCopyableStorageVisitor : public StorageVisitor {
 
   bool visitMemberDecl(ValueDecl *storage, Type ty);
   bool visitMemberType(Type type, SourceLoc loc);
-  bool isUnchecked(ProtocolConformanceRef conformance);
   bool visitNonconformingMemberType(Type type, SourceLoc loc);
   void emitNonconformingMemberTypeDiagnostic(Type ty, SourceLoc loc);
 };
@@ -137,13 +136,6 @@ bool BitwiseCopyableStorageVisitor::visitMemberType(Type ty, SourceLoc loc) {
     return visitNonconformingMemberType(ty, loc);
   }
 
-  if (isImplicit(check) && isUnchecked(conformance)) {
-    // Do not automatically derive conformance if one of the field's
-    // conformance is @unchecked.
-    invalid = true;
-    return true;
-  }
-
   // Walk the conformance, diagnosing any missing BitwiseCopyable conformances.
   bool anyMissing = false;
   conformance.forEachMissingConformance(
@@ -158,20 +150,6 @@ bool BitwiseCopyableStorageVisitor::visitMemberType(Type ty, SourceLoc loc) {
   return anyMissing;
 }
 
-bool BitwiseCopyableStorageVisitor::isUnchecked(
-    ProtocolConformanceRef conformance) {
-  if (!conformance.isConcrete())
-    return false;
-  auto concrete = conformance.getConcrete();
-  assert(concrete);
-  auto *root = concrete->getRootConformance();
-  assert(root);
-  auto *normal = dyn_cast<NormalProtocolConformance>(root);
-  if (!normal)
-    return false;
-  return normal->isUnchecked();
-}
-
 bool BitwiseCopyableStorageVisitor::visitNonconformingMemberType(
     Type ty, SourceLoc loc) {
   if (ty->hasError())

lib/Sema/TypeCheckProtocol.cpp

@@ -2165,8 +2165,7 @@ static void diagnoseConformanceImpliedByConditionalConformance(
 /// to the given protocol. This should return true when @unchecked can be
 /// used to disable those semantic checks.
 static bool hasAdditionalSemanticChecks(ProtocolDecl *proto) {
-  return proto->isSpecificProtocol(KnownProtocolKind::Sendable) ||
-         proto->isSpecificProtocol(KnownProtocolKind::BitwiseCopyable);
+  return proto->isSpecificProtocol(KnownProtocolKind::Sendable);
 }
 
 /// Determine whether the type \c T conforms to the protocol \c Proto,

test/Sema/bitwise_copyable.swift

@@ -94,21 +94,6 @@ struct S_Explicit_With_Metatype_Optional_AnyObject : _BitwiseCopyable {
   var ty: Optional<AnyObject>.Type
 }
 
-struct S_Unchecked : @unchecked _BitwiseCopyable {}
-
-struct S_Implicit_With_S_Unchecked {
-  var s: S_Unchecked
-}
-
-func passS_Implicit_With_S_Unchecked(_ s: S_Implicit_With_S_Unchecked) {
-  take1(s) // expected-error{{type_does_not_conform_decl_owner}}
-           // expected-note@-92 {{where_requirement_failure_one_subst}}
-}
-
-struct S_Explicit_With_S_Unchecked : _BitwiseCopyable {
-  var s: S_Unchecked
-}
-
 //==============================================================================
 //===========================DEPENDENCY-FREE TESTS=(END)======================}}
 //==============================================================================