Merge pull request #3658 from slavapestov/replace-noreturn-with-never

SE-0102: Remove @NoReturn attribute and introduce an empty Never type

Author: slavapestov

include/swift/AST/ASTContext.h

@@ -440,11 +440,15 @@ class ASTContext {
   /// Retrieve the declaration of the "pointee" property of a pointer type.
   VarDecl *getPointerPointeePropertyDecl(PointerTypeKind ptrKind) const;
 
+  /// Retrieve the declaration of Swift.Never.
+  NominalTypeDecl *getNeverDecl() const;
+  CanType getNeverType() const;
+
   /// Retrieve the declaration of Swift.Void.
   TypeAliasDecl *getVoidDecl() const;
 
   /// Retrieve the declaration of ObjectiveC.ObjCBool.
-  StructDecl *getObjCBoolDecl();
+  StructDecl *getObjCBoolDecl() const;
 
   /// Retrieve the declaration of Foundation.NSError.
   ClassDecl *getNSErrorDecl() const;
@@ -481,7 +485,7 @@ class ASTContext {
   /// Retrieve the declaration of Swift.==(Int, Int) -> Bool.
   FuncDecl *getEqualIntDecl(LazyResolver *resolver) const;
 
-  /// Retrieve the declaration of Swift._unimplemented_initializer.
+  /// Retrieve the declaration of Swift._unimplementedInitializer.
   FuncDecl *getUnimplementedInitializerDecl(LazyResolver *resolver) const;
 
   /// Retrieve the declaration of Swift._undefined.
@@ -491,7 +495,7 @@ class ASTContext {
   FuncDecl *getIsOSVersionAtLeastDecl(LazyResolver *resolver) const;
 
   /// Look for the declaration with the given name within the
-  /// swift module.
+  /// Swift module.
   void lookupInSwiftModule(StringRef name,
                            SmallVectorImpl<ValueDecl *> &results) const;
 

include/swift/AST/Builtins.def

@@ -431,10 +431,10 @@ BUILTIN_MISC_OPERATION(ZeroInitializer, "zeroInitializer", "n", Special)
 /// once has type (Builtin.RawPointer, () -> ())
 BUILTIN_MISC_OPERATION(Once, "once", "", Special)
 
-/// unreachable has type @noreturn () -> ()
+/// unreachable has type () -> Never
 BUILTIN_MISC_OPERATION(Unreachable, "unreachable", "", Special)
 
-/// conditionallyUnreachable has type @noreturn () -> ()
+/// conditionallyUnreachable has type () -> Never
 BUILTIN_MISC_OPERATION(CondUnreachable, "conditionallyUnreachable", "", Special)
 
 /// DestroyArray has type (T.Type, Builtin.RawPointer, Builtin.Word) -> ()

include/swift/AST/DiagnosticsSIL.def

@@ -179,8 +179,6 @@ ERROR(assignment_to_immutable_value,none,
 ERROR(missing_return,none,
       "missing return in a %select{function|closure}1 expected to return %0",
       (Type, unsigned))
-ERROR(return_from_noreturn,none, 
-      "return from a 'noreturn' function", ())
 ERROR(non_exhaustive_switch,none, 
       "switch must be exhaustive, consider adding a default clause", ())
 ERROR(guard_body_must_not_fallthrough,none,
@@ -190,7 +188,7 @@ WARNING(unreachable_code,none, "will never be executed", ())
 NOTE(unreachable_code_branch,none,
      "condition always evaluates to %select{false|true}0", (bool))
 NOTE(call_to_noreturn_note,none,
-     "a call to a noreturn function", ())
+     "a call to a never-returning function", ())
 WARNING(unreachable_code_after_stmt,none,
         "code after '%select{return|break|continue|throw}0' will never "
         "be executed", (unsigned))

include/swift/AST/DiagnosticsSema.def

@@ -1015,7 +1015,7 @@ NOTE(note_no_in_class_init_3plus,none,
      "without initial values prevent synthesized initializers",
      (Identifier, Identifier, Identifier, bool))
 ERROR(missing_unimplemented_init_runtime,none,
-      "standard library error: missing _unimplemented_initializer", ())
+      "standard library error: missing _unimplementedInitializer", ())
 ERROR(missing_undefined_runtime,none,
       "standard library error: missing _undefined", ())
 WARNING(unsupported_synthesize_init_variadic,none,

include/swift/AST/Types.h

@@ -392,7 +392,10 @@ class alignas(1 << TypeAlignInBits) TypeBase {
   /// hasReferenceSemantics() - Do objects of this type have reference
   /// semantics?
   bool hasReferenceSemantics();
-  
+
+  /// Is this an uninhabited type, such as 'Never'?
+  bool isNever();
+
   /// Is this the 'Any' type?
   bool isAny();
 
@@ -751,10 +754,6 @@ class alignas(1 << TypeAlignInBits) TypeBase {
   /// parameter replaced. Only makes sense for function members of types.
   Type replaceSelfParameterType(Type newSelf);
 
-  /// Returns a function type that is not 'noreturn', but is otherwise the same
-  /// as this type.
-  Type getWithoutNoReturn(unsigned UncurryLevel);
-
   /// getRValueType - For an @lvalue type, retrieves the underlying object type.
   /// Otherwise, returns the type itself.
   Type getRValueType();

include/swift/SIL/SILFunction.h

@@ -215,6 +215,8 @@ class SILFunction
     return LoweredType;
   }
 
+  bool isNoReturnFunction() const;
+
   /// Unsafely rewrite the lowered type of this function.
   ///
   /// This routine does not touch the entry block arguments

include/swift/SIL/SILInstruction.h

@@ -1002,6 +1002,10 @@ class ApplyInstBase<Impl, Base, false> : public Base {
     return SubstCalleeType;
   }
 
+  bool isCalleeNoReturn() const {
+    return getSubstCalleeSILType().isNoReturnFunction();
+  }
+
   bool isCalleeThin() const {
     auto Rep = getSubstCalleeType()->getRepresentation();
     return Rep == FunctionType::Representation::Thin;
@@ -5077,6 +5081,11 @@ class ApplySite {
     FOREACH_IMPL_RETURN(getSubstCalleeSILType());
   }
 
+  /// Check if this is a call of a never-returning function.
+  bool isCalleeNoReturn() const {
+    FOREACH_IMPL_RETURN(isCalleeNoReturn());
+  }
+
   bool isCalleeThin() const {
     switch (getSubstCalleeType()->getRepresentation()) {
     case SILFunctionTypeRepresentation::CFunctionPointer:

include/swift/SIL/SILType.h

@@ -285,7 +285,11 @@ class SILType {
   /// True if the type, or the referenced type of an address type, is a
   /// scalar reference-counted type.
   bool isReferenceCounted(SILModule &M) const;
-  
+
+  /// Returns true if the referenced type is a function type that never
+  /// returns.
+  bool isNoReturnFunction() const;
+
   /// Returns true if the referenced type has reference semantics.
   bool hasReferenceSemantics() const {
     return getSwiftRValueType().hasReferenceSemantics();

lib/AST/ASTContext.cpp

@@ -155,6 +155,9 @@ struct ASTContext::Implementation {
   /// The declaration of Swift.Unmanaged<T>
   NominalTypeDecl *UnmanagedDecl = nullptr;
 
+  /// The declaration of Swift.Never.
+  NominalTypeDecl *NeverDecl = nullptr;
+
   /// The declaration of Swift.Void.
   TypeAliasDecl *VoidDecl = nullptr;
 
@@ -180,7 +183,7 @@ struct ASTContext::Implementation {
   /// func ==(Int, Int) -> Bool
   FuncDecl *EqualIntDecl = nullptr;
 
-  /// func _unimplemented_initializer(className: StaticString).
+  /// func _unimplementedInitializer(className: StaticString).
   FuncDecl *UnimplementedInitializerDecl = nullptr;
 
   /// func _undefined<T>(msg: StaticString, file: StaticString, line: UInt) -> T
@@ -710,7 +713,7 @@ NominalTypeDecl *ASTContext::getUnsafeMutablePointerDecl() const {
 NominalTypeDecl *ASTContext::getOpaquePointerDecl() const {
   if (!Impl.OpaquePointerDecl)
     Impl.OpaquePointerDecl
-    = findStdlibType(*this, "OpaquePointer", 0);
+      = findStdlibType(*this, "OpaquePointer", 0);
 
   return Impl.OpaquePointerDecl;
 }
@@ -784,6 +787,17 @@ ASTContext::getPointerPointeePropertyDecl(PointerTypeKind ptrKind) const {
   llvm_unreachable("bad pointer kind");
 }
 
+NominalTypeDecl *ASTContext::getNeverDecl() const {
+  if (!Impl.NeverDecl)
+    Impl.NeverDecl = findStdlibType(*this, "Never", 0);
+  
+  return Impl.NeverDecl;
+}
+
+CanType ASTContext::getNeverType() const {
+  return getNeverDecl()->getDeclaredType()->getCanonicalType();
+}
+
 TypeAliasDecl *ASTContext::getVoidDecl() const {
   if (Impl.VoidDecl) {
     return Impl.VoidDecl;
@@ -802,10 +816,11 @@ TypeAliasDecl *ASTContext::getVoidDecl() const {
   return Impl.VoidDecl;
 }
 
-StructDecl *ASTContext::getObjCBoolDecl() {
+StructDecl *ASTContext::getObjCBoolDecl() const {
   if (!Impl.ObjCBoolDecl) {
     SmallVector<ValueDecl *, 1> results;
-    if (Module *M = getModuleByName(Id_ObjectiveC.str())) {
+    auto *Context = const_cast<ASTContext *>(this);
+    if (Module *M = Context->getModuleByName(Id_ObjectiveC.str())) {
       M->lookupValue({ }, getIdentifier("ObjCBool"), NLKind::UnqualifiedLookup,
                      results);
       for (auto result : results) {
@@ -1004,7 +1019,7 @@ ASTContext::getUnimplementedInitializerDecl(LazyResolver *resolver) const {
 
   // Look for the function.
   CanType input, output;
-  auto decl = findLibraryIntrinsic(*this, "_unimplemented_initializer",
+  auto decl = findLibraryIntrinsic(*this, "_unimplementedInitializer",
                                    resolver);
   if (!decl || !isNonGenericIntrinsic(decl, input, output))
     return nullptr;

lib/AST/Builtins.cpp

@@ -713,8 +713,7 @@ static ValueDecl *getVoidErrorOperation(ASTContext &Context, Identifier Id) {
 static ValueDecl *getUnexpectedErrorOperation(ASTContext &Context,
                                               Identifier Id) {
   return getBuiltinFunction(Id, {Context.getExceptionType()},
-                            TupleType::getEmpty(Context),
-                            AnyFunctionType::ExtInfo().withIsNoReturn());
+                            Context.getNeverType());
 }
 
 static ValueDecl *getCmpXChgOperation(ASTContext &Context, Identifier Id,
@@ -974,10 +973,8 @@ static ValueDecl *getIntToFPWithOverflowOperation(ASTContext &Context,
 
 static ValueDecl *getUnreachableOperation(ASTContext &Context,
                                           Identifier Id) {
-  // @noreturn () -> ()
-  auto VoidTy = Context.TheEmptyTupleType;
-  return getBuiltinFunction(Id, {}, VoidTy,
-                            AnyFunctionType::ExtInfo().withIsNoReturn(true));
+  // () -> Never
+  return getBuiltinFunction(Id, {}, Context.getNeverType());
 }
 
 static ValueDecl *getOnceOperation(ASTContext &Context,
@@ -1192,7 +1189,7 @@ getSwiftFunctionTypeForIntrinsic(unsigned iid, ArrayRef<Type> TypeArgs,
   Info = FunctionType::ExtInfo();
   if (attrs.hasAttribute(llvm::AttributeSet::FunctionIndex,
                          llvm::Attribute::NoReturn))
-    Info = Info.withIsNoReturn(true);
+    ResultTy = Context.getNeverType();
 
   return true;
 }

lib/AST/Type.cpp

@@ -89,6 +89,15 @@ bool TypeBase::hasReferenceSemantics() {
   return getCanonicalType().hasReferenceSemantics();
 }
 
+bool TypeBase::isNever() {
+  if (auto nominalDecl = getAnyNominal())
+    if (auto enumDecl = dyn_cast<EnumDecl>(nominalDecl))
+      if (enumDecl->getAllElements().empty())
+        return true;
+
+  return false;
+}
+
 bool TypeBase::isAny() {
   return isEqual(getASTContext().TheAnyType);
 }
@@ -919,27 +928,6 @@ Type TypeBase::replaceSelfParameterType(Type newSelf) {
                            fnTy->getExtInfo());
 }
 
-Type TypeBase::getWithoutNoReturn(unsigned UncurryLevel) {
-  if (UncurryLevel == 0)
-    return this;
-
-  auto *FnType = this->castTo<AnyFunctionType>();
-  Type InputType = FnType->getInput();
-  Type ResultType = FnType->getResult()->getWithoutNoReturn(UncurryLevel - 1);
-  auto TheExtInfo = FnType->getExtInfo().withIsNoReturn(false);
-  if (auto *GFT = dyn_cast<GenericFunctionType>(FnType)) {
-    return GenericFunctionType::get(GFT->getGenericSignature(),
-                                    InputType, ResultType,
-                                    TheExtInfo);
-  }
-  if (auto *PFT = dyn_cast<PolymorphicFunctionType>(FnType)) {
-    return PolymorphicFunctionType::get(InputType, ResultType,
-                                        &PFT->getGenericParams(),
-                                        TheExtInfo);
-  }
-  return FunctionType::get(InputType, ResultType, TheExtInfo);
-}
-
 /// Retrieve the object type for a 'self' parameter, digging into one-element
 /// tuples, inout types, and metatypes.
 Type TypeBase::getRValueInstanceType() {

lib/ClangImporter/ImportDecl.cpp

@@ -3428,10 +3428,6 @@ namespace {
 
     void finishFuncDecl(const clang::FunctionDecl *decl,
                         AbstractFunctionDecl *result) {
-      if (decl->isNoReturn())
-        result->getAttrs().add(new (Impl.SwiftContext)
-                                   NoReturnAttr(/*IsImplicit=*/false));
-
       // Keep track of inline function bodies so that we can generate
       // IR from them using Clang's IR generator.
       if ((decl->isInlined() || decl->hasAttr<clang::AlwaysInlineAttr>() ||

lib/ClangImporter/ImportType.cpp

@@ -1518,12 +1518,12 @@ importFunctionType(DeclContext *dc,
   if (!parameterList)
     return Type();
 
-  FunctionType::ExtInfo extInfo;
-  extInfo = extInfo.withIsNoReturn(isNoReturn);
+  if (isNoReturn)
+    swiftResultTy = SwiftContext.getNeverType();
 
   // Form the function type.
   auto argTy = parameterList->getType(SwiftContext);
-  return FunctionType::get(argTy, swiftResultTy, extInfo);
+  return FunctionType::get(argTy, swiftResultTy);
 }
 
 ParameterList *ClangImporter::Implementation::importFunctionParameterList(
@@ -2430,9 +2430,13 @@ Type ClangImporter::Implementation::importMethodType(
 
   // Form the parameter list.
   *bodyParams = ParameterList::create(SwiftContext, swiftParams);
-  
+
+  if (isNoReturn) {
+    origSwiftResultTy = SwiftContext.getNeverType();
+    swiftResultTy = SwiftContext.getNeverType();
+  }
+
   FunctionType::ExtInfo extInfo;
-  extInfo = extInfo.withIsNoReturn(isNoReturn);
 
   if (errorInfo) {
     foreignErrorInfo = getForeignErrorInfo(*errorInfo, errorParamType,

lib/IDE/CodeCompletion.cpp

@@ -4063,7 +4063,7 @@ class CompletionOverrideLookup : public swift::VisibleDeclConsumer {
         Options.setArchetypeSelfTransform(transformType, VD->getDeclContext());
       Options.PrintDefaultParameterPlaceholder = false;
       Options.PrintImplicitAttrs = false;
-      Options.ExclusiveAttrList.push_back(DAK_NoReturn);
+      Options.SkipAttributes = true;
       Options.PrintOverrideKeyword = false;
       Options.PrintPropertyAccessors = false;
       VD->print(Printer, Options);
@@ -4141,7 +4141,7 @@ class CompletionOverrideLookup : public swift::VisibleDeclConsumer {
       llvm::raw_svector_ostream OS(DeclStr);
       PrintOptions Options;
       Options.PrintImplicitAttrs = false;
-      Options.ExclusiveAttrList.push_back(DAK_NoReturn);
+      Options.SkipAttributes = true;
       Options.PrintDefaultParameterPlaceholder = false;
       CD->print(OS, Options);
     }

lib/IRGen/GenClangType.cpp

@@ -489,6 +489,11 @@ GenClangType::visitBoundGenericType(CanBoundGenericType type) {
 }
 
 clang::CanQualType GenClangType::visitEnumType(CanEnumType type) {
+  // Special case: Uninhabited enums are not @objc, so we don't
+  // know what to do below, but we can just convert to 'void'.
+  if (type->isNever())
+    return Converter.convert(IGM, IGM.Context.TheEmptyTupleType);
+
   assert(type->getDecl()->isObjC() && "not an @objc enum?!");
 
   // @objc enums lower to their raw types.

lib/SIL/SILFunction.cpp

@@ -294,6 +294,11 @@ Type SILFunction::mapTypeOutOfContext(Type type) const {
                                                type);
 }
 
+bool SILFunction::isNoReturnFunction() const {
+  return SILType::getPrimitiveObjectType(getLoweredFunctionType())
+      .isNoReturnFunction();
+}
+
 SILBasicBlock *SILFunction::createBasicBlock() {
   return new (getModule()) SILBasicBlock(this);
 }

lib/SIL/SILType.cpp

@@ -70,6 +70,17 @@ bool SILType::isReferenceCounted(SILModule &M) const {
   return M.getTypeLowering(*this).isReferenceCounted();
 }
 
+bool SILType::isNoReturnFunction() const {
+  if (auto funcTy = dyn_cast<SILFunctionType>(getSwiftRValueType())) {
+    if (funcTy->isNoReturn())
+      return true;
+
+    return funcTy->getSILResult().getSwiftRValueType()->isNever();
+  }
+
+  return false;
+}
+
 std::string SILType::getAsString() const {
   std::string Result;
   llvm::raw_string_ostream OS(Result);

lib/SIL/SILVerifier.cpp

@@ -797,7 +797,7 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
     // Check that if the apply is of a noreturn callee, make sure that an
     // unreachable is the next instruction.
     if (AI->getModule().getStage() == SILStage::Raw ||
-        !AI->getCallee()->getType().getAs<SILFunctionType>()->isNoReturn())
+        !AI->isCalleeNoReturn())
       return;
     require(isa<UnreachableInst>(std::next(SILBasicBlock::iterator(AI))),
             "No return apply without an unreachable as a next instruction.");