[clang] Add a new nullability annotation for swift async: _Nullable_result

_Nullable_result generally like _Nullable, except when being imported into a
swift async method. rdar://70106409

Differential revision: https://reviews.llvm.org/D92495

Author: epilk

clang/include/clang-c/Index.h

@@ -3861,7 +3861,15 @@ enum CXTypeNullabilityKind {
   /**
    * Nullability is not applicable to this type.
    */
-  CXTypeNullability_Invalid = 3
+  CXTypeNullability_Invalid = 3,
+
+  /**
+   * Generally behaves like Nullable, except when used in a block parameter that
+   * was imported into a swift async method. There, swift will assume that the
+   * parameter can get null even if no error occured. _Nullable parameters are
+   * assumed to only get null on error.
+   */
+  CXTypeNullability_NullableResult = 4
 };
 
 /**

clang/include/clang/AST/Type.h

@@ -4716,6 +4716,9 @@ class AttributedType : public Type, public llvm::FoldingSetNode {
     case NullabilityKind::Nullable:
       return attr::TypeNullable;
 
+    case NullabilityKind::NullableResult:
+      return attr::TypeNullableResult;
+
     case NullabilityKind::Unspecified:
       return attr::TypeNullUnspecified;
     }

clang/include/clang/Basic/Attr.td

@@ -1805,6 +1805,11 @@ def TypeNullable : TypeAttr {
   let Documentation = [TypeNullableDocs];
 }
 
+def TypeNullableResult : TypeAttr {
+  let Spellings = [Keyword<"_Nullable_result">];
+  let Documentation = [TypeNullableResultDocs];
+}
+
 def TypeNullUnspecified : TypeAttr {
   let Spellings = [Keyword<"_Null_unspecified">];
   let Documentation = [TypeNullUnspecifiedDocs];

clang/include/clang/Basic/AttrDocs.td

@@ -3508,6 +3508,29 @@ a caller of ``fetch_or_zero`` can provide null.
   }];
 }
 
+def TypeNullableResultDocs : Documentation {
+  let Category = NullabilityDocs;
+  let Content = [{
+The ``_Nullable_result`` nullability qualifier means that a value of the
+``_Nullable_result`` pointer can be ``nil``, just like ``_Nullable``. Where this
+attribute differs from ``_Nullable`` is when it's used on a parameter to a
+completion handler in a Swift async method. For instance, here:
+
+  .. code-block:: objc
+
+    -(void)fetchSomeDataWithID:(int)identifier
+             completionHandler:(void (^)(Data *_Nullable_result result, NSError *error))completionHandler;
+
+This method asynchronously calls ``completionHandler`` when the data is
+available, or calls it with an error. ``_Nullable_result`` indicates to the
+Swift importer that this is the uncommon case where ``result`` can get ``nil``
+even if no error has occured, and will therefore import it as a Swift optional
+type. Otherwise, if ``result`` was annotated with ``_Nullable``, the Swift
+importer will assume that ``result`` will always be non-nil unless an error
+occured.
+}];
+}
+
 def TypeNullUnspecifiedDocs : Documentation {
   let Category = NullabilityDocs;
   let Content = [{

clang/include/clang/Basic/Features.def

@@ -85,6 +85,7 @@ FEATURE(cxx_rtti, LangOpts.RTTI &&LangOpts.RTTIData)
 FEATURE(enumerator_attributes, true)
 FEATURE(nullability, true)
 FEATURE(nullability_on_arrays, true)
+FEATURE(nullability_nullable_result, true)
 FEATURE(memory_sanitizer,
         LangOpts.Sanitize.hasOneOf(SanitizerKind::Memory |
                                    SanitizerKind::KernelMemory))

clang/include/clang/Basic/Specifiers.h

@@ -309,7 +309,12 @@ namespace clang {
     /// unspecified. This captures a (fairly rare) case where we
     /// can't conclude anything about the nullability of the type even
     /// though it has been considered.
-    Unspecified
+    Unspecified,
+    // Generally behaves like Nullable, except when used in a block parameter
+    // that was imported into a swift async method. There, swift will assume
+    // that the parameter can get null even if no error occured. _Nullable
+    // parameters are assumed to only get null on error.
+    NullableResult,
   };
 
   /// Return true if \p L has a weaker nullability annotation than \p R. The

clang/include/clang/Basic/TokenKinds.def

@@ -650,6 +650,7 @@ ALIAS("__volatile__" , volatile   , KEYALL)
 // Type nullability.
 KEYWORD(_Nonnull                 , KEYALL)
 KEYWORD(_Nullable                , KEYALL)
+KEYWORD(_Nullable_result         , KEYALL)
 KEYWORD(_Null_unspecified        , KEYALL)
 
 // Microsoft extensions which should be disabled in strict conformance mode

clang/include/clang/Sema/Sema.h

@@ -12448,6 +12448,7 @@ class Sema final {
   /// Nullability type specifiers.
   IdentifierInfo *Ident__Nonnull = nullptr;
   IdentifierInfo *Ident__Nullable = nullptr;
+  IdentifierInfo *Ident__Nullable_result = nullptr;
   IdentifierInfo *Ident__Null_unspecified = nullptr;
 
   IdentifierInfo *Ident_NSError = nullptr;

clang/lib/APINotes/APINotesYAMLCompiler.cpp

@@ -89,6 +89,7 @@ template <> struct ScalarEnumerationTraits<NullabilityKind> {
     IO.enumCase(NK, "Nonnull", NullabilityKind::NonNull);
     IO.enumCase(NK, "Optional", NullabilityKind::Nullable);
     IO.enumCase(NK, "Unspecified", NullabilityKind::Unspecified);
+    IO.enumCase(NK, "NullableResult", NullabilityKind::NullableResult);
     // TODO: Mapping this to it's own value would allow for better cross
     // checking. Also the default should be Unknown.
     IO.enumCase(NK, "Scalar", NullabilityKind::Unspecified);

clang/lib/AST/Type.cpp

@@ -3512,6 +3512,7 @@ bool AttributedType::isQualifier() const {
   case attr::ObjCInertUnsafeUnretained:
   case attr::TypeNonNull:
   case attr::TypeNullable:
+  case attr::TypeNullableResult:
   case attr::TypeNullUnspecified:
   case attr::LifetimeBound:
   case attr::AddressSpace:
@@ -4159,6 +4160,8 @@ AttributedType::getImmediateNullability() const {
     return NullabilityKind::Nullable;
   if (getAttrKind() == attr::TypeNullUnspecified)
     return NullabilityKind::Unspecified;
+  if (getAttrKind() == attr::TypeNullableResult)
+    return NullabilityKind::NullableResult;
   return None;
 }
 

clang/lib/AST/TypePrinter.cpp

@@ -1579,6 +1579,8 @@ void TypePrinter::printAttributedBefore(const AttributedType *T,
       OS << " _Nullable";
     else if (T->getAttrKind() == attr::TypeNullUnspecified)
       OS << " _Null_unspecified";
+    else if (T->getAttrKind() == attr::TypeNullableResult)
+      OS << " _Nullable_result";
     else
       llvm_unreachable("unhandled nullability");
     spaceBeforePlaceHolder(OS);
@@ -1649,6 +1651,7 @@ void TypePrinter::printAttributedAfter(const AttributedType *T,
   case attr::LifetimeBound:
   case attr::TypeNonNull:
   case attr::TypeNullable:
+  case attr::TypeNullableResult:
   case attr::TypeNullUnspecified:
   case attr::ObjCGC:
   case attr::ObjCInertUnsafeUnretained:

clang/lib/Basic/Diagnostic.cpp

@@ -55,6 +55,12 @@ const StreamingDiagnostic &clang::operator<<(const StreamingDiagnostic &DB,
   case NullabilityKind::Unspecified:
     string = nullability.second ? "'null_unspecified'" : "'_Null_unspecified'";
     break;
+
+  case NullabilityKind::NullableResult:
+    assert(!nullability.second &&
+           "_Nullable_result isn't supported as context-sensitive keyword");
+    string = "_Nullable_result";
+    break;
   }
 
   DB.AddString(string);

clang/lib/Basic/IdentifierTable.cpp

@@ -714,6 +714,11 @@ StringRef clang::getNullabilitySpelling(NullabilityKind kind,
   case NullabilityKind::Nullable:
     return isContextSensitive ? "nullable" : "_Nullable";
 
+  case NullabilityKind::NullableResult:
+    assert(!isContextSensitive &&
+           "_Nullable_result isn't supported as context-sensitive keyword");
+    return "_Nullable_result";
+
   case NullabilityKind::Unspecified:
     return isContextSensitive ? "null_unspecified" : "_Null_unspecified";
   }

clang/lib/Parse/ParseDecl.cpp

@@ -833,6 +833,7 @@ void Parser::ParseNullabilityTypeSpecifiers(ParsedAttributes &attrs) {
     switch (Tok.getKind()) {
     case tok::kw__Nonnull:
     case tok::kw__Nullable:
+    case tok::kw__Nullable_result:
     case tok::kw__Null_unspecified: {
       IdentifierInfo *AttrName = Tok.getIdentifierInfo();
       SourceLocation AttrNameLoc = ConsumeToken();
@@ -3536,6 +3537,7 @@ void Parser::ParseDeclarationSpecifiers(DeclSpec &DS,
     // Nullability type specifiers.
     case tok::kw__Nonnull:
     case tok::kw__Nullable:
+    case tok::kw__Nullable_result:
     case tok::kw__Null_unspecified:
       ParseNullabilityTypeSpecifiers(DS.getAttributes());
       continue;
@@ -5022,6 +5024,7 @@ bool Parser::isTypeSpecifierQualifier() {
 
   case tok::kw__Nonnull:
   case tok::kw__Nullable:
+  case tok::kw__Nullable_result:
   case tok::kw__Null_unspecified:
 
   case tok::kw___kindof:
@@ -5249,6 +5252,7 @@ bool Parser::isDeclarationSpecifier(bool DisambiguatingWithExpression) {
 
   case tok::kw__Nonnull:
   case tok::kw__Nullable:
+  case tok::kw__Nullable_result:
   case tok::kw__Null_unspecified:
 
   case tok::kw___kindof:
@@ -5524,6 +5528,7 @@ void Parser::ParseTypeQualifierListOpt(
     // Nullability type specifiers.
     case tok::kw__Nonnull:
     case tok::kw__Nullable:
+    case tok::kw__Nullable_result:
     case tok::kw__Null_unspecified:
       ParseNullabilityTypeSpecifiers(DS.getAttributes());
       continue;

clang/lib/Parse/ParseTentative.cpp

@@ -842,7 +842,8 @@ Parser::TPResult Parser::TryParsePtrOperatorSeq() {
 
       while (Tok.isOneOf(tok::kw_const, tok::kw_volatile, tok::kw_restrict,
                          tok::kw__Nonnull, tok::kw__Nullable,
-                         tok::kw__Null_unspecified, tok::kw__Atomic))
+                         tok::kw__Nullable_result, tok::kw__Null_unspecified,
+                         tok::kw__Atomic))
         ConsumeToken();
     } else {
       return TPResult::True;
@@ -1437,6 +1438,7 @@ Parser::isCXXDeclarationSpecifier(Parser::TPResult BracedCastResult,
   case tok::kw___unaligned:
   case tok::kw__Nonnull:
   case tok::kw__Nullable:
+  case tok::kw__Nullable_result:
   case tok::kw__Null_unspecified:
   case tok::kw___kindof:
     return TPResult::True;

clang/lib/Sema/Sema.cpp

@@ -503,7 +503,8 @@ void Sema::diagnoseNullableToNonnullConversion(QualType DstType,
                                                QualType SrcType,
                                                SourceLocation Loc) {
   Optional<NullabilityKind> ExprNullability = SrcType->getNullability(Context);
-  if (!ExprNullability || *ExprNullability != NullabilityKind::Nullable)
+  if (!ExprNullability || (*ExprNullability != NullabilityKind::Nullable &&
+                           *ExprNullability != NullabilityKind::NullableResult))
     return;
 
   Optional<NullabilityKind> TypeNullability = DstType->getNullability(Context);

clang/lib/Sema/SemaCodeComplete.cpp

@@ -2700,6 +2700,10 @@ static std::string formatObjCParamQualifiers(unsigned ObjCQuals,
       case NullabilityKind::Unspecified:
         Result += "null_unspecified ";
         break;
+
+      case NullabilityKind::NullableResult:
+        llvm_unreachable("Not supported as a context-sensitive keyword!");
+        break;
       }
     }
   }

clang/lib/Sema/SemaExpr.cpp

@@ -8562,8 +8562,12 @@ static QualType computeConditionalNullability(QualType ResTy, bool IsBin,
 
   auto GetNullability = [&Ctx](QualType Ty) {
     Optional<NullabilityKind> Kind = Ty->getNullability(Ctx);
-    if (Kind)
+    if (Kind) {
+      // For our purposes, treat _Nullable_result as _Nullable.
+      if (*Kind == NullabilityKind::NullableResult)
+        return NullabilityKind::Nullable;
       return *Kind;
+    }
     return NullabilityKind::Unspecified;
   };
 

clang/lib/Sema/SemaExprObjC.cpp

@@ -1563,12 +1563,20 @@ QualType Sema::getMessageSendResultType(const Expr *Receiver,
 
   // Map the nullability of the result into a table index.
   unsigned receiverNullabilityIdx = 0;
-  if (auto nullability = ReceiverType->getNullability(Context))
+  if (Optional<NullabilityKind> nullability =
+          ReceiverType->getNullability(Context)) {
+    if (*nullability == NullabilityKind::NullableResult)
+      nullability = NullabilityKind::Nullable;
     receiverNullabilityIdx = 1 + static_cast<unsigned>(*nullability);
+  }
 
   unsigned resultNullabilityIdx = 0;
-  if (auto nullability = resultType->getNullability(Context))
+  if (Optional<NullabilityKind> nullability =
+          resultType->getNullability(Context)) {
+    if (*nullability == NullabilityKind::NullableResult)
+      nullability = NullabilityKind::Nullable;
     resultNullabilityIdx = 1 + static_cast<unsigned>(*nullability);
+  }
 
   // The table of nullability mappings, indexed by the receiver's nullability
   // and then the result type's nullability.

clang/lib/Sema/SemaType.cpp

@@ -147,6 +147,7 @@ static void diagnoseBadTypeAttribute(Sema &S, const ParsedAttr &attr,
 #define NULLABILITY_TYPE_ATTRS_CASELIST                                        \
   case ParsedAttr::AT_TypeNonNull:                                             \
   case ParsedAttr::AT_TypeNullable:                                            \
+  case ParsedAttr::AT_TypeNullableResult:                                      \
   case ParsedAttr::AT_TypeNullUnspecified
 
 namespace {
@@ -3893,6 +3894,11 @@ IdentifierInfo *Sema::getNullabilityKeyword(NullabilityKind nullability) {
       Ident__Nullable = PP.getIdentifierInfo("_Nullable");
     return Ident__Nullable;
 
+  case NullabilityKind::NullableResult:
+    if (!Ident__Nullable_result)
+      Ident__Nullable_result = PP.getIdentifierInfo("_Nullable_result");
+    return Ident__Nullable_result;
+
   case NullabilityKind::Unspecified:
     if (!Ident__Null_unspecified)
       Ident__Null_unspecified = PP.getIdentifierInfo("_Null_unspecified");
@@ -3915,6 +3921,7 @@ static bool hasNullabilityAttr(const ParsedAttributesView &attrs) {
   for (const ParsedAttr &AL : attrs) {
     if (AL.getKind() == ParsedAttr::AT_TypeNonNull ||
         AL.getKind() == ParsedAttr::AT_TypeNullable ||
+        AL.getKind() == ParsedAttr::AT_TypeNullableResult ||
         AL.getKind() == ParsedAttr::AT_TypeNullUnspecified)
       return true;
   }
@@ -4333,6 +4340,9 @@ static Attr *createNullabilityAttr(ASTContext &Ctx, ParsedAttr &Attr,
   case NullabilityKind::Nullable:
     return createSimpleAttr<TypeNullableAttr>(Ctx, Attr);
 
+  case NullabilityKind::NullableResult:
+    return createSimpleAttr<TypeNullableResultAttr>(Ctx, Attr);
+
   case NullabilityKind::Unspecified:
     return createSimpleAttr<TypeNullUnspecifiedAttr>(Ctx, Attr);
   }
@@ -7008,6 +7018,9 @@ static NullabilityKind mapNullabilityAttrKind(ParsedAttr::Kind kind) {
   case ParsedAttr::AT_TypeNullable:
     return NullabilityKind::Nullable;
 
+  case ParsedAttr::AT_TypeNullableResult:
+    return NullabilityKind::NullableResult;
+
   case ParsedAttr::AT_TypeNullUnspecified:
     return NullabilityKind::Unspecified;
 

clang/test/Index/nullability.c

@@ -2,9 +2,11 @@ int *a;
 int * _Nonnull b;
 int * _Nullable c;
 int * _Null_unspecified d;
+int * _Nullable_result e;
 
 // RUN: env CINDEXTEST_INCLUDE_ATTRIBUTED_TYPES=1 c-index-test -test-print-type %s | FileCheck %s
 // CHECK: VarDecl=a:1:6 [type=int *] [typekind=Pointer] [isPOD=1] [pointeetype=int] [pointeekind=Int]
 // CHECK: VarDecl=b:2:16 [type=int * _Nonnull] [typekind=Attributed] [nullability=nonnull] [canonicaltype=int *] [canonicaltypekind=Pointer] [modifiedtype=int *] [modifiedtypekind=Pointer] [isPOD=1]
 // CHECK: VarDecl=c:3:17 [type=int * _Nullable] [typekind=Attributed] [nullability=nullable] [canonicaltype=int *] [canonicaltypekind=Pointer] [modifiedtype=int *] [modifiedtypekind=Pointer] [isPOD=1]
 // CHECK: VarDecl=d:4:25 [type=int * _Null_unspecified] [typekind=Attributed] [nullability=unspecified] [canonicaltype=int *] [canonicaltypekind=Pointer] [modifiedtype=int *] [modifiedtypekind=Pointer] [isPOD=1]
+// CHECK: VarDecl=e:5:24 [type=int * _Nullable_result] [typekind=Attributed] [nullability=nullable_result] [canonicaltype=int *] [canonicaltypekind=Pointer] [modifiedtype=int *] [modifiedtypekind=Pointer] [isPOD=1]

clang/test/SemaObjC/nullability.m

@@ -116,11 +116,13 @@ - (id)returnsNone;
 - (nonnull id)returnsNonNull;
 - (nullable id)returnsNullable;
 - (null_unspecified id)returnsNullUnspecified;
+- (_Nullable_result id)returnsNullableResult;
 @end
 
 void test_receiver_merge(NSMergeReceiver *none,
                          _Nonnull NSMergeReceiver *nonnull,
                          _Nullable NSMergeReceiver *nullable,
+                         _Nullable_result NSMergeReceiver *nullable_result,
                          _Null_unspecified NSMergeReceiver *null_unspecified) {
   int *ptr;
 
@@ -129,6 +131,12 @@ void test_receiver_merge(NSMergeReceiver *none,
   ptr = [nullable returnsNonNull]; // expected-warning{{'id _Nullable'}}
   ptr = [nullable returnsNone]; // expected-warning{{'id _Nullable'}}
 
+  ptr = [nullable_result returnsNullable]; // expected-warning{{'id _Nullable'}}
+  ptr = [nullable_result returnsNullUnspecified]; // expected-warning{{'id _Nullable'}}
+  ptr = [nullable_result returnsNonNull]; // expected-warning{{'id _Nullable'}}
+  ptr = [nullable_result returnsNone]; // expected-warning{{'id _Nullable'}}
+  ptr = [nullable_result returnsNullableResult]; // expected-warning{{'id _Nullable_result'}}
+
   ptr = [null_unspecified returnsNullable]; // expected-warning{{'id _Nullable'}}
   ptr = [null_unspecified returnsNullUnspecified]; // expected-warning{{'id _Null_unspecified'}}
   ptr = [null_unspecified returnsNonNull]; // expected-warning{{'id _Null_unspecified'}}
@@ -237,6 +245,7 @@ void conditional_expr(int c) {
   NSFoo * _Nonnull nonnullP;
   NSFoo * _Nullable nullableP;
   NSFoo * _Null_unspecified unspecifiedP;
+  NSFoo * _Nullable_result nullableResultP;
   NSFoo *noneP;
 
   p = c ? nonnullP : nonnullP;
@@ -255,6 +264,10 @@ void conditional_expr(int c) {
   p = c ? noneP : nullableP; // expected-warning{{implicit conversion from nullable pointer 'NSFoo * _Nullable' to non-nullable pointer type 'NSFoo * _Nonnull'}}
   p = c ? noneP : unspecifiedP;
   p = c ? noneP : noneP;
+  p = c ? noneP : nullableResultP; // expected-warning{{implicit conversion from nullable pointer 'NSFoo * _Nullable' to non-nullable pointer type 'NSFoo * _Nonnull'}}
+  p = c ? nonnullP : nullableResultP; // expected-warning{{implicit conversion from nullable pointer 'NSFoo * _Nullable' to non-nullable pointer type 'NSFoo * _Nonnull'}}
+  p = c ? nullableP : nullableResultP; // expected-warning{{implicit conversion from nullable pointer 'NSFoo * _Nullable' to non-nullable pointer type 'NSFoo * _Nonnull'}}
+  p = c ? nullableResultP : nullableResultP; // expected-warning{{implicit conversion from nullable pointer 'NSFoo * _Nullable_result' to non-nullable pointer type 'NSFoo * _Nonnull'}}
 }
 
 typedef int INTS[4];