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

4 files changed, 8 insertions, 0 deletions

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 1ea44fe6006..d6b9424fb4d 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -2040,6 +2040,8 @@ bool ASTNodeImporter::ImportDefinition(RecordDecl *From, RecordDecl *To,
     ToData.HasIrrelevantDestructor = FromData.HasIrrelevantDestructor;
     ToData.HasConstexprNonCopyMoveConstructor
       = FromData.HasConstexprNonCopyMoveConstructor;
+    ToData.HasDefaultedDefaultConstructor
+      = FromData.HasDefaultedDefaultConstructor;
     ToData.DefaultedDefaultConstructorIsConstexpr
       = FromData.DefaultedDefaultConstructorIsConstexpr;
     ToData.HasConstexprDefaultConstructor
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) {
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index bf60ba9478a..5ef31c31bfa 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -1423,6 +1423,7 @@ void ASTDeclReader::ReadCXXDefinitionData(
   Data.DeclaredNonTrivialSpecialMembers = Record[Idx++];
   Data.HasIrrelevantDestructor = Record[Idx++];
   Data.HasConstexprNonCopyMoveConstructor = Record[Idx++];
+  Data.HasDefaultedDefaultConstructor = Record[Idx++];
   Data.DefaultedDefaultConstructorIsConstexpr = Record[Idx++];
   Data.HasConstexprDefaultConstructor = Record[Idx++];
   Data.HasNonLiteralTypeFieldsOrBases = Record[Idx++];
@@ -1548,6 +1549,7 @@ void ASTDeclReader::MergeDefinitionData(
   OR_FIELD(DeclaredNonTrivialSpecialMembers)
   MATCH_FIELD(HasIrrelevantDestructor)
   OR_FIELD(HasConstexprNonCopyMoveConstructor)
+  OR_FIELD(HasDefaultedDefaultConstructor)
   MATCH_FIELD(DefaultedDefaultConstructorIsConstexpr)
   OR_FIELD(HasConstexprDefaultConstructor)
   MATCH_FIELD(HasNonLiteralTypeFieldsOrBases)
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 1d1c99874b6..a88ab5fb5f2 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -5558,6 +5558,7 @@ void ASTWriter::AddCXXDefinitionData(const CXXRecordDecl *D, RecordDataImpl &Rec
   Record.push_back(Data.DeclaredNonTrivialSpecialMembers);
   Record.push_back(Data.HasIrrelevantDestructor);
   Record.push_back(Data.HasConstexprNonCopyMoveConstructor);
+  Record.push_back(Data.HasDefaultedDefaultConstructor);
   Record.push_back(Data.DefaultedDefaultConstructorIsConstexpr);
   Record.push_back(Data.HasConstexprDefaultConstructor);
   Record.push_back(Data.HasNonLiteralTypeFieldsOrBases);