[Sema] Make nullness warnings appear in C++.

Given the following code:

    int *_Nullable ptr;
    int *_Nonnull nn = ptr;

...In C, clang will warn you about `nn = ptr`, because you're assigning
a nonnull pointer to a nullable pointer. In C++, clang issues no such
warning. This patch helps ensure that clang doesn't ever miss an
opportunity to complain about C++ code.

N.B. Though this patch has a differential revision link, the actual
review took place over email.

Differential Revision: http://reviews.llvm.org/D14938

llvm-svn: 255556

1 files changed, 15 insertions, 12 deletions

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index b87fb52f4d2..39b8cc9f0c6 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -349,6 +349,20 @@ void Sema::PrintStats() const {
   AnalysisWarnings.PrintStats();
 }
 
+void Sema::diagnoseNullableToNonnullConversion(QualType DstType,
+                                               QualType SrcType,
+                                               SourceLocation Loc) {
+  Optional<NullabilityKind> ExprNullability = SrcType->getNullability(Context);
+  if (!ExprNullability || *ExprNullability != NullabilityKind::Nullable)
+    return;
+
+  Optional<NullabilityKind> TypeNullability = DstType->getNullability(Context);
+  if (!TypeNullability || *TypeNullability != NullabilityKind::NonNull)
+    return;
+
+  Diag(Loc, diag::warn_nullability_lost) << SrcType << DstType;
+}
+
 /// 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.
@@ -372,18 +386,7 @@ ExprResult Sema::ImpCastExprToType(Expr *E, QualType Ty,
   assert((VK == VK_RValue || !E->isRValue()) && "can't cast rvalue to lvalue");
 #endif
 
-  // Check whether we're implicitly casting from a nullable type to a nonnull
-  // type.
-  if (auto exprNullability = E->getType()->getNullability(Context)) {
-    if (*exprNullability == NullabilityKind::Nullable) {
-      if (auto typeNullability = Ty->getNullability(Context)) {
-        if (*typeNullability == NullabilityKind::NonNull) {
-          Diag(E->getLocStart(), diag::warn_nullability_lost)
-            << E->getType() << Ty;
-        }
-      }
-    }
-  }
+  diagnoseNullableToNonnullConversion(Ty, E->getType(), E->getLocStart());
 
   QualType ExprTy = Context.getCanonicalType(E->getType());
   QualType TypeTy = Context.getCanonicalType(Ty);