Fix rejects-valid caused by r261297.

r261297 called hasUserProvidedDefaultConstructor() to check if defining a
const object is ok.  This is incorrect for this example:

  struct X { template<typename ...T> X(T...); int n; };
  const X x; // formerly OK, now bogus error

Instead, track if a class has a defaulted default constructor, and disallow
a const object for classes that either have defaulted default constructors or
if they need an implicit constructor.

Bug report and fix approach by Richard Smith, thanks!

llvm-svn: 261770

1 files changed, 3 insertions, 0 deletions

diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index e84b91388fb..65bfc49daec 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -61,6 +61,7 @@ CXXRecordDecl::DefinitionData::DefinitionData(CXXRecordDecl *D)
       DefaultedDestructorIsDeleted(false), HasTrivialSpecialMembers(SMF_All),
       DeclaredNonTrivialSpecialMembers(0), HasIrrelevantDestructor(true),
       HasConstexprNonCopyMoveConstructor(false),
+      HasDefaultedDefaultConstructor(false),
       DefaultedDefaultConstructorIsConstexpr(true),
       HasConstexprDefaultConstructor(false),
       HasNonLiteralTypeFieldsOrBases(false), ComputedVisibleConversions(false),
@@ -497,6 +498,8 @@ void CXXRecordDecl::addedMember(Decl *D) {
         data().UserProvidedDefaultConstructor = true;
       if (Constructor->isConstexpr())
         data().HasConstexprDefaultConstructor = true;
+      if (Constructor->isDefaulted())
+        data().HasDefaultedDefaultConstructor = true;
     }
 
     if (!FunTmpl) {