[BitwiseCopyable] Don't infer on unref storage.

An imported declaration which has storage that can't be represented in
Swift must not be inferred to be BitwiseCopyable: that inference
involves looking at the (visible) fields.

Author: nate-chandler

include/swift/AST/DiagnosticsSema.def

@@ -7650,6 +7650,8 @@ ERROR(non_bitwise_copyable_type_nonescapable,none,
       "nonescapable type cannot conform to 'BitwiseCopyable'", ())
 ERROR(non_bitwise_copyable_type_cxx_nontrivial,none,
       "non-trivial C++ type cannot conform to 'BitwiseCopyable'", ())
+ERROR(non_bitwise_copyable_c_type_nontrivial,none,
+      "type with unrepresentable fields cannot derive conformance to 'BitwiseCopyable'", ())
 ERROR(non_bitwise_copyable_type_member,none,
       "%select{stored property %2|associated value %2}1 of "
       "'BitwiseCopyable'-conforming %kind3 has non-bitwise-copyable type %0",

lib/Sema/TypeCheckBitwise.cpp

@@ -269,6 +269,13 @@ static bool checkBitwiseCopyableInstanceStorage(NominalTypeDecl *nominal,
     return true;
   }
 
+  if (sd && sd->hasUnreferenceableStorage()) {
+    if (!isImplicit(check)) {
+      sd->diagnose(diag::non_bitwise_copyable_c_type_nontrivial);
+    }
+    return true;
+  }
+
   BitwiseCopyableStorageVisitor visitor(nominal, dc, check);
 
   return visitor.visit(nominal, dc) || visitor.invalid;

test/Sema/bitwse_copyable_import.swift

@@ -42,6 +42,18 @@ struct VoidPointers {
   void *p10;
 };
 
+struct IntsTrailing {
+  double d;
+  float f;
+  int is[];
+};
+
+struct IntsTrailing2 {
+  double d;
+  float f;
+  int is[];
+};
+
 //--- Downstream.swift
 
 func take<T : _BitwiseCopyable>(_ t: T) {}
@@ -56,3 +68,11 @@ func passVoidPointers(_ t: VoidPointers) {
   take(t) 
   take(t.p10)
 }
+func passIntsTrailing(_ t: IntsTrailing) {
+  take(t) // expected-error{{type_does_not_conform_decl_owner}}
+          // expected-note@-14{{where_requirement_failure_one_subst}}
+}
+extension IntsTrailing2 : _BitwiseCopyable {} //expected-error{{bitwise_copyable_outside_module}}
+func passIntsTrailing2(_ t: IntsTrailing2) {
+  take(t)
+}