CWG1423: don't permit implicit conversion of nullptr_t to bool.

The C++ rules briefly allowed this, but the rule changed nearly 10 years
ago and we never updated our implementation to match. However, we've
warned on this by default for a long time, and no other compiler accepts
(even as an extension).

1 files changed, 21 insertions, 4 deletions

diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 61b7c16..61bb1f0 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -4420,16 +4420,20 @@ static void TryListInitialization(Sema &S,
     // direct-list-initialization and copy-initialization otherwise.
     // We can't use InitListChecker for this, because it always performs
     // copy-initialization. This only matters if we might use an 'explicit'
-    // conversion operator, so we only need to handle the cases where the source
-    // is of record type.
-    if (InitList->getInit(0)->getType()->isRecordType()) {
+    // conversion operator, or for the special case conversion of nullptr_t to
+    // bool, so we only need to handle those cases.
+    //
+    // FIXME: Why not do this in all cases?
+    Expr *Init = InitList->getInit(0);
+    if (Init->getType()->isRecordType() ||
+        (Init->getType()->isNullPtrType() && DestType->isBooleanType())) {
       InitializationKind SubKind =
           Kind.getKind() == InitializationKind::IK_DirectList
               ? InitializationKind::CreateDirect(Kind.getLocation(),
                                                  InitList->getLBraceLoc(),
                                                  InitList->getRBraceLoc())
               : Kind;
-      Expr *SubInit[1] = { InitList->getInit(0) };
+      Expr *SubInit[1] = { Init };
       Sequence.InitializeFrom(S, Entity, SubKind, SubInit,
                               /*TopLevelOfInitList*/true,
                               TreatUnavailableAsInvalid);
@@ -5854,6 +5858,19 @@ void InitializationSequence::InitializeFrom(Sema &S,
     return;
   }
 
+  //    - Otherwise, if the initialization is direct-initialization, the source
+  //    type is std::nullptr_t, and the destination type is bool, the initial
+  //    value of the object being initialized is false.
+  if (!SourceType.isNull() && SourceType->isNullPtrType() &&
+      DestType->isBooleanType() &&
+      Kind.getKind() == InitializationKind::IK_Direct) {
+    AddConversionSequenceStep(
+        ImplicitConversionSequence::getNullptrToBool(SourceType, DestType,
+                                                     Initializer->isGLValue()),
+        DestType);
+    return;
+  }
+
   //    - Otherwise, the initial value of the object being initialized is the
   //      (possibly converted) value of the initializer expression. Standard
   //      conversions (Clause 4) will be used, if necessary, to convert the