Introduce Wzero-as-null-pointer-constant.

Add an opt-in warning that fires when 0 is used as a null pointer. 
gcc has this warning, and there's some demand for it.

https://reviews.llvm.org/D32914

llvm-svn: 302247

1 files changed, 14 insertions, 0 deletions

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 94e792c1d17..2f493fa5fbe 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -383,6 +383,19 @@ void Sema::diagnoseNullableToNonnullConversion(QualType DstType,
   Diag(Loc, diag::warn_nullability_lost) << SrcType << DstType;
 }
 
+void Sema::diagnoseZeroToNullptrConversion(CastKind Kind, const Expr* E) {
+  if (Kind != CK_NullToPointer && Kind != CK_NullToMemberPointer)
+    return;
+  if (E->getType()->isNullPtrType())
+    return;
+  // nullptr only exists from C++11 on, so don't warn on its absence earlier.
+  if (!getLangOpts().CPlusPlus11)
+    return;
+
+  Diag(E->getLocStart(), diag::warn_zero_as_null_pointer_constant)
+      << FixItHint::CreateReplacement(E->getSourceRange(), "nullptr");
+}
+
 /// ImpCastExprToType - If Expr is not of type 'Type', insert an implicit cast.
 /// If there is already an implicit cast, merge into the existing one.
 /// The result is of the given category.
@@ -407,6 +420,7 @@ ExprResult Sema::ImpCastExprToType(Expr *E, QualType Ty,
 #endif
 
   diagnoseNullableToNonnullConversion(Ty, E->getType(), E->getLocStart());
+  diagnoseZeroToNullptrConversion(Kind, E);
 
   QualType ExprTy = Context.getCanonicalType(E->getType());
   QualType TypeTy = Context.getCanonicalType(Ty);