DR1359: A constexpr constructor does not need to initialize an empty struct or

empty union. This still rejects anonymous member structs or unions which only
contain such empty class types, pending standard wording defining exactly what
an empty class type is.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150157 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 5 deletions

diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 62332b8b4a..8ba84fe86a 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -815,7 +815,11 @@ static void CheckConstexprCtorInitializer(Sema &SemaRef,
                                           bool &Diagnosed) {
   if (Field->isUnnamedBitfield())
     return;
-  
+
+  if (Field->isAnonymousStructOrUnion() &&
+      Field->getType()->getAsCXXRecordDecl()->isEmpty())
+    return;
+
   if (!Inits.count(Field)) {
     if (!Diagnosed) {
       SemaRef.Diag(Dcl->getLocation(), diag::err_constexpr_ctor_missing_init);
@@ -901,11 +905,14 @@ bool Sema::CheckConstexprFunctionBody(const FunctionDecl *Dcl, Stmt *Body,
   if (const CXXConstructorDecl *Constructor
         = dyn_cast<CXXConstructorDecl>(Dcl)) {
     const CXXRecordDecl *RD = Constructor->getParent();
-    // - every non-static data member and base class sub-object shall be
-    //   initialized;
+    // DR1359:
+    // - every non-variant non-static data member and base class sub-object
+    //   shall be initialized;
+    // - if the class is a non-empty union, or for each non-empty anonymous
+    //   union member of a non-union class, exactly one non-static data member
+    //   shall be initialized;
     if (RD->isUnion()) {
-      // DR1359: Exactly one member of a union shall be initialized.
-      if (Constructor->getNumCtorInitializers() == 0) {
+      if (Constructor->getNumCtorInitializers() == 0 && !RD->isEmpty()) {
         Diag(Dcl->getLocation(), diag::err_constexpr_union_ctor_no_init);
         return false;
       }