Fix implicit conversion from _Nullable to _Nonnull warnings in C++

[george.burgess.iv]

Summary

Currently, code like this compiles cleanly in C++, but with warnings (as it should) in C:

int foo() {
  void *_Nullable p;
  void *_Nonnull n = p;
}

This patch makes us emit the appropriate warnings in C++.

@doug.gregor: arc said you would be best to review this; if you're unable to, I'm happy to ping others. :)

[george.burgess.iv]

Ping :)

[george.burgess.iv]

Ping :)

cfe/trunk/include/clang/Sema/Sema.h

public:
   /// \p PossibleBody, has a suspicious null statement as a body.
   void DiagnoseEmptyLoopBody(const Stmt *S,
                              const Stmt *PossibleBody);
 
   /// Warn if a value is moved to itself.
   void DiagnoseSelfMove(const Expr *LHSExpr, const Expr *RHSExpr,
                         SourceLocation OpLoc);
 
+  /// \brief Warn if we're implicitly casting from a _Nullable pointer type to a
+  /// _Nonnull one.
+  void diagnoseNullableToNonnullConversion(QualType DstType, QualType SrcType,
+                                           SourceLocation Loc);
+
   ParsingDeclState PushParsingDeclaration(sema::DelayedDiagnosticPool &pool) {
     return DelayedDiagnostics.push(pool);
   }
   void PopParsingDeclaration(ParsingDeclState state, Decl *decl);
 
   typedef ProcessingContextState ParsingClassState;
   ParsingClassState PushParsingClass() {
     return DelayedDiagnostics.pushUndelayed();

cfe/trunk/lib/Sema/Sema.cpp

 void Sema::PrintStats() const {
   llvm::errs() << "\n*** Semantic Analysis Stats:\n";
   llvm::errs() << NumSFINAEErrors << " SFINAE diagnostics trapped.\n";
 
   BumpAlloc.PrintStats();
   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.
 ExprResult Sema::ImpCastExprToType(Expr *E, QualType Ty,
                                    CastKind Kind, ExprValueKind VK,
                                    const CXXCastPath *BasePath,
                                    CheckedConversionKind CCK) {
 #ifndef NDEBUG
   if (VK == VK_RValue && !E->isRValue()) {
     switch (Kind) {
     default:
       llvm_unreachable("can't implicitly cast lvalue to rvalue with this cast "
                        "kind");
     case CK_LValueToRValue:
     case CK_ArrayToPointerDecay:
     case CK_FunctionToPointerDecay:
     case CK_ToVoid:
       break;
     }
   }
   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);
 
   if (ExprTy == TypeTy)
     return E;
 
   if (ImplicitCastExpr *ImpCast = dyn_cast<ImplicitCastExpr>(E)) {

cfe/trunk/lib/Sema/SemaExprCXX.cpp

Sema::PerformImplicitConversion(Expr *From, QualType ToType,
   // If we're converting to an atomic type, first convert to the corresponding
   // non-atomic type.
   QualType ToAtomicType;
   if (const AtomicType *ToAtomic = ToType->getAs<AtomicType>()) {
     ToAtomicType = ToType;
     ToType = ToAtomic->getValueType();
   }
 
+  QualType InitialFromType = FromType;
   // Perform the first implicit conversion.
   switch (SCS.First) {
   case ICK_Identity:
     if (const AtomicType *FromAtomic = FromType->getAs<AtomicType>()) {
       FromType = FromAtomic->getValueType().getUnqualifiedType();
       From = ImplicitCastExpr::Create(Context, FromType, CK_AtomicToNonAtomic,
                                       From, /*BasePath=*/nullptr, VK_RValue);
     }
Sema::PerformImplicitConversion(Expr *From, QualType ToType,
   // that conversion now.
   if (!ToAtomicType.isNull()) {
     assert(Context.hasSameType(
         ToAtomicType->castAs<AtomicType>()->getValueType(), From->getType()));
     From = ImpCastExprToType(From, ToAtomicType, CK_NonAtomicToAtomic,
                              VK_RValue, nullptr, CCK).get();
   }
 
+  // If this conversion sequence succeeded and involved implicitly converting a
+  // _Nullable type to a _Nonnull one, complain.
+  if (CCK == CCK_ImplicitConversion)
+    diagnoseNullableToNonnullConversion(ToType, InitialFromType,
+                                        From->getLocStart());
+
   return From;
 }
 
 /// \brief Check the completeness of a type in a unary type trait.
 ///
 /// If the particular type trait requires a complete type, tries to complete
 /// it. If completing the type fails, a diagnostic is emitted and false
 /// returned. If completing the type succeeds or no completion was required,

cfe/trunk/test/Sema/nullability.c

_Nonnull int *returns_int_ptr(int x) {
 
   return (_Nonnull int *)0;
 }
 
 // Check nullable-to-nonnull conversions.
 void nullable_to_nonnull(_Nullable int *ptr) {
   int *a = ptr; // okay
   _Nonnull int *b = ptr; // expected-warning{{implicit conversion from nullable pointer 'int * _Nullable' to non-nullable pointer type 'int * _Nonnull'}}
+  b = ptr; // expected-warning{{implicit conversion from nullable pointer 'int * _Nullable' to non-nullable pointer type 'int * _Nonnull'}}
+
+  accepts_nonnull_1(ptr); // expected-warning{{implicit conversion from nullable pointer 'int * _Nullable' to non-nullable pointer type 'int * _Nonnull'}}
 }

cfe/trunk/test/SemaCXX/nullability.cpp

-// RUN: %clang_cc1 -std=c++11 -fsyntax-only -Wno-nullability-declspec %s -verify
+// RUN: %clang_cc1 -std=c++11 -fsyntax-only -Wno-nullability-declspec %s -verify -Wnullable-to-nonnull-conversion
 
 #if __has_feature(nullability)
 #else
 #  error nullability feature should be defined
 #endif
 
 typedef decltype(nullptr) nullptr_t;
 

 }
 
 template<void FP(_Nonnull int*)> 
 void test_accepts_nonnull_null_pointer_literal_template() {
   FP(0); // expected-warning{{null passed to a callee that requires a non-null argument}}
 }
 
 template void test_accepts_nonnull_null_pointer_literal_template<&accepts_nonnull_4>(); // expected-note{{instantiation of function template specialization}}
+
+void TakeNonnull(void *_Nonnull);
+// Check different forms of assignment to a nonull type from a nullable one.
+void AssignAndInitNonNull() {
+  void *_Nullable nullable;
+  void *_Nonnull p(nullable); // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+  void *_Nonnull p2{nullable}; // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+  void *_Nonnull p3 = {nullable}; // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+  void *_Nonnull p4 = nullable; // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+  void *_Nonnull nonnull;
+  nonnull = nullable; // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+  nonnull = {nullable}; // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+
+  TakeNonnull(nullable); //expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull}}
+  TakeNonnull(nonnull); // OK
+}
+
+void *_Nullable ReturnNullable();
+
+void AssignAndInitNonNullFromFn() {
+  void *_Nonnull p(ReturnNullable()); // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+  void *_Nonnull p2{ReturnNullable()}; // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+  void *_Nonnull p3 = {ReturnNullable()}; // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+  void *_Nonnull p4 = ReturnNullable(); // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+  void *_Nonnull nonnull;
+  nonnull = ReturnNullable(); // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+  nonnull = {ReturnNullable()}; // expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull'}}
+
+  TakeNonnull(ReturnNullable()); //expected-warning{{implicit conversion from nullable pointer 'void * _Nullable' to non-nullable pointer type 'void * _Nonnull}}
+}