[Clang] [C++26] Implement P2573R2: = delete("should have a reason"); (llvm#86526)

This implements support for the `= delete("message")` syntax that was
only just added to C++26
([P2573R2](https://isocpp.org/files/papers/P2573R2.html#proposal-scope)).

Author: Sirraide

clang/docs/LanguageExtensions.rst

@@ -1493,6 +1493,7 @@ Conditional ``explicit``                     __cpp_conditional_explicit       C+
 ``if consteval``                             __cpp_if_consteval               C++23         C++20
 ``static operator()``                        __cpp_static_call_operator       C++23         C++03
 Attributes on Lambda-Expressions                                              C++23         C++11
+``= delete ("should have a reason");``       __cpp_deleted_function           C++26         C++03
 -------------------------------------------- -------------------------------- ------------- -------------
 Designated initializers (N494)                                                C99           C89
 Array & element qualification (N2607)                                         C23           C89

clang/docs/ReleaseNotes.rst

@@ -129,6 +129,8 @@ C++2c Feature Support
 
 - Implemented `P2662R3 Pack Indexing <https://wg21.link/P2662R3>`_.
 
+- Implemented `P2573R2: = delete("should have a reason"); <https://wg21.link/P2573R2>`_
+
 
 Resolutions to C++ Defect Reports
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/AST/Decl.h

@@ -1993,21 +1993,35 @@ class FunctionDecl : public DeclaratorDecl,
 
   };
 
-  /// Stashed information about a defaulted function definition whose body has
-  /// not yet been lazily generated.
-  class DefaultedFunctionInfo final
-      : llvm::TrailingObjects<DefaultedFunctionInfo, DeclAccessPair> {
+  /// Stashed information about a defaulted/deleted function body.
+  class DefaultedOrDeletedFunctionInfo final
+      : llvm::TrailingObjects<DefaultedOrDeletedFunctionInfo, DeclAccessPair,
+                              StringLiteral *> {
     friend TrailingObjects;
     unsigned NumLookups;
+    bool HasDeletedMessage;
+
+    size_t numTrailingObjects(OverloadToken<DeclAccessPair>) const {
+      return NumLookups;
+    }
 
   public:
-    static DefaultedFunctionInfo *Create(ASTContext &Context,
-                                         ArrayRef<DeclAccessPair> Lookups);
+    static DefaultedOrDeletedFunctionInfo *
+    Create(ASTContext &Context, ArrayRef<DeclAccessPair> Lookups,
+           StringLiteral *DeletedMessage = nullptr);
+
     /// Get the unqualified lookup results that should be used in this
     /// defaulted function definition.
     ArrayRef<DeclAccessPair> getUnqualifiedLookups() const {
       return {getTrailingObjects<DeclAccessPair>(), NumLookups};
     }
+
+    StringLiteral *getDeletedMessage() const {
+      return HasDeletedMessage ? *getTrailingObjects<StringLiteral *>()
+                               : nullptr;
+    }
+
+    void setDeletedMessage(StringLiteral *Message);
   };
 
 private:
@@ -2017,12 +2031,12 @@ class FunctionDecl : public DeclaratorDecl,
   ParmVarDecl **ParamInfo = nullptr;
 
   /// The active member of this union is determined by
-  /// FunctionDeclBits.HasDefaultedFunctionInfo.
+  /// FunctionDeclBits.HasDefaultedOrDeletedInfo.
   union {
     /// The body of the function.
     LazyDeclStmtPtr Body;
     /// Information about a future defaulted function definition.
-    DefaultedFunctionInfo *DefaultedInfo;
+    DefaultedOrDeletedFunctionInfo *DefaultedOrDeletedInfo;
   };
 
   unsigned ODRHash;
@@ -2280,18 +2294,18 @@ class FunctionDecl : public DeclaratorDecl,
 
   /// Returns whether this specific declaration of the function has a body.
   bool doesThisDeclarationHaveABody() const {
-    return (!FunctionDeclBits.HasDefaultedFunctionInfo && Body) ||
+    return (!FunctionDeclBits.HasDefaultedOrDeletedInfo && Body) ||
            isLateTemplateParsed();
   }
 
   void setBody(Stmt *B);
   void setLazyBody(uint64_t Offset) {
-    FunctionDeclBits.HasDefaultedFunctionInfo = false;
+    FunctionDeclBits.HasDefaultedOrDeletedInfo = false;
     Body = LazyDeclStmtPtr(Offset);
   }
 
-  void setDefaultedFunctionInfo(DefaultedFunctionInfo *Info);
-  DefaultedFunctionInfo *getDefaultedFunctionInfo() const;
+  void setDefaultedOrDeletedInfo(DefaultedOrDeletedFunctionInfo *Info);
+  DefaultedOrDeletedFunctionInfo *getDefalutedOrDeletedInfo() const;
 
   /// Whether this function is variadic.
   bool isVariadic() const;
@@ -2494,7 +2508,7 @@ class FunctionDecl : public DeclaratorDecl,
     return FunctionDeclBits.IsDeleted && !isDefaulted();
   }
 
-  void setDeletedAsWritten(bool D = true) { FunctionDeclBits.IsDeleted = D; }
+  void setDeletedAsWritten(bool D = true, StringLiteral *Message = nullptr);
 
   /// Determines whether this function is "main", which is the
   /// entry point into an executable program.
@@ -2650,6 +2664,13 @@ class FunctionDecl : public DeclaratorDecl,
       AC.push_back(TRC);
   }
 
+  /// Get the message that indicates why this function was deleted.
+  StringLiteral *getDeletedMessage() const {
+    return FunctionDeclBits.HasDefaultedOrDeletedInfo
+               ? DefaultedOrDeletedInfo->getDeletedMessage()
+               : nullptr;
+  }
+
   void setPreviousDeclaration(FunctionDecl * PrevDecl);
 
   FunctionDecl *getCanonicalDecl() override;

clang/include/clang/AST/DeclBase.h

@@ -1739,7 +1739,7 @@ class DeclContext {
     LLVM_PREFERRED_TYPE(bool)
     uint64_t IsExplicitlyDefaulted : 1;
     LLVM_PREFERRED_TYPE(bool)
-    uint64_t HasDefaultedFunctionInfo : 1;
+    uint64_t HasDefaultedOrDeletedInfo : 1;
 
     /// For member functions of complete types, whether this is an ineligible
     /// special member function or an unselected destructor. See

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -941,6 +941,12 @@ def warn_cxx98_compat_defaulted_deleted_function : Warning<
   "%select{defaulted|deleted}0 function definitions are incompatible with C++98">,
   InGroup<CXX98Compat>, DefaultIgnore;
 
+def ext_delete_with_message : ExtWarn<
+  "'= delete' with a message is a C++2c extension">, InGroup<CXX26>;
+def warn_cxx23_delete_with_message : Warning<
+  "'= delete' with a message is incompatible with C++ standards before C++2c">,
+  DefaultIgnore, InGroup<CXXPre26Compat>;
+
 // C++11 default member initialization
 def ext_nonstatic_member_init : ExtWarn<
   "default member initializer for non-static data member is a C++11 "

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -4683,11 +4683,10 @@ def err_ovl_no_viable_member_function_in_call : Error<
   "no matching member function for call to %0">;
 def err_ovl_ambiguous_call : Error<
   "call to %0 is ambiguous">;
-def err_ovl_deleted_call : Error<"call to deleted function %0">;
+def err_ovl_deleted_call : Error<"call to deleted"
+  "%select{| member}0 function %1%select{|: %3}2">;
 def err_ovl_ambiguous_member_call : Error<
   "call to member function %0 is ambiguous">;
-def err_ovl_deleted_member_call : Error<
-  "call to deleted member function %0">;
 def note_ovl_too_many_candidates : Note<
     "remaining %0 candidate%s0 omitted; "
     "pass -fshow-overloads=all to show them">;
@@ -4915,12 +4914,12 @@ def err_ovl_ambiguous_conversion_in_cast : Error<
   "dynamic_cast|C-style cast|functional-style cast|}0 from %1 to %2">;
 def err_ovl_deleted_conversion_in_cast : Error<
   "%select{|static_cast|reinterpret_cast|dynamic_cast|C-style cast|"
-  "functional-style cast|}0 from %1 to %2 uses deleted function">;
+  "functional-style cast|}0 from %1 to %2 uses deleted function%select{|: %4}3">;
 def err_ovl_ambiguous_init : Error<"call to constructor of %0 is ambiguous">;
 def err_ref_init_ambiguous : Error<
   "reference initialization of type %0 with initializer of type %1 is ambiguous">;
 def err_ovl_deleted_init : Error<
-  "call to deleted constructor of %0">;
+  "call to deleted constructor of %0%select{|: %2}1">;
 def err_ovl_deleted_special_init : Error<
   "call to implicitly-deleted %select{default constructor|copy constructor|"
   "move constructor|copy assignment operator|move assignment operator|"
@@ -4946,7 +4945,7 @@ def note_ovl_ambiguous_oper_binary_reversed_candidate : Note<
 def err_ovl_no_viable_oper : Error<"no viable overloaded '%0'">;
 def note_assign_lhs_incomplete : Note<"type %0 is incomplete">;
 def err_ovl_deleted_oper : Error<
-  "overload resolution selected deleted operator '%0'">;
+  "overload resolution selected deleted operator '%0'%select{|: %2}1">;
 def err_ovl_deleted_special_oper : Error<
   "object of type %0 cannot be %select{constructed|copied|moved|assigned|"
   "assigned|destroyed}1 because its %sub{select_special_member_kind}1 is "
@@ -4983,7 +4982,7 @@ def err_ovl_ambiguous_object_call : Error<
 def err_ovl_ambiguous_subscript_call : Error<
   "call to subscript operator of type %0 is ambiguous">;
 def err_ovl_deleted_object_call : Error<
-  "call to deleted function call operator in type %0">;
+  "call to deleted function call operator in type %0%select{|: %2}1">;
 def note_ovl_surrogate_cand : Note<"conversion candidate of type %0">;
 def err_member_call_without_object : Error<
   "call to %select{non-static|explicit}0 member function without an object argument">;
@@ -8284,7 +8283,7 @@ def err_typecheck_nonviable_condition_incomplete : Error<
   "no viable conversion%diff{ from $ to incomplete type $|}0,1">;
 def err_typecheck_deleted_function : Error<
   "conversion function %diff{from $ to $|between types}0,1 "
-  "invokes a deleted function">;
+  "invokes a deleted function%select{|: %3}2">;
 
 def err_expected_class_or_namespace : Error<"%0 is not a class"
   "%select{ or namespace|, namespace, or enumeration}1">;
@@ -8884,7 +8883,7 @@ def err_nontemporal_builtin_must_be_pointer_intfltptr_or_vector : Error<
   "address argument to nontemporal builtin must be a pointer to integer, float, "
   "pointer, or a vector of such types (%0 invalid)">;
 
-def err_deleted_function_use : Error<"attempt to use a deleted function">;
+def err_deleted_function_use : Error<"attempt to use a deleted function%select{|: %1}0">;
 def err_deleted_inherited_ctor_use : Error<
   "constructor inherited by %0 from base class %1 is implicitly deleted">;
 

clang/include/clang/Parse/Parser.h

@@ -1601,6 +1601,8 @@ class Parser : public CodeCompletionHandler {
                                      const ParsedTemplateInfo &TemplateInfo,
                                      const VirtSpecifiers &VS,
                                      SourceLocation PureSpecLoc);
+  StringLiteral *ParseCXXDeletedFunctionMessage();
+  void SkipDeletedFunctionBody();
   void ParseCXXNonStaticMemberInitializer(Decl *VarD);
   void ParseLexedAttributes(ParsingClass &Class);
   void ParseLexedAttributeList(LateParsedAttrList &LAs, Decl *D,

clang/include/clang/Sema/Sema.h

@@ -3045,14 +3045,18 @@ class Sema final : public SemaBase {
   void ActOnDocumentableDecls(ArrayRef<Decl *> Group);
 
   enum class FnBodyKind {
-    /// C++ [dcl.fct.def.general]p1
+    /// C++26 [dcl.fct.def.general]p1
     /// function-body:
     ///   ctor-initializer[opt] compound-statement
     ///   function-try-block
     Other,
     ///   = default ;
     Default,
+    ///   deleted-function-body
+    ///
+    /// deleted-function-body:
     ///   = delete ;
+    ///   = delete ( unevaluated-string ) ;
     Delete
   };
 
@@ -4751,10 +4755,12 @@ class Sema final : public SemaBase {
                                SourceLocation EqualLoc);
 
   void ActOnPureSpecifier(Decl *D, SourceLocation PureSpecLoc);
-  void SetDeclDeleted(Decl *dcl, SourceLocation DelLoc);
+  void SetDeclDeleted(Decl *dcl, SourceLocation DelLoc,
+                      StringLiteral *Message = nullptr);
   void SetDeclDefaulted(Decl *dcl, SourceLocation DefaultLoc);
 
-  void SetFunctionBodyKind(Decl *D, SourceLocation Loc, FnBodyKind BodyKind);
+  void SetFunctionBodyKind(Decl *D, SourceLocation Loc, FnBodyKind BodyKind,
+                           StringLiteral *DeletedMessage = nullptr);
   void ActOnStartTrailingRequiresClause(Scope *S, Declarator &D);
   ExprResult ActOnFinishTrailingRequiresClause(ExprResult ConstraintExpr);
   ExprResult ActOnRequiresClause(ExprResult ConstraintExpr);
@@ -8093,6 +8099,11 @@ class Sema final : public SemaBase {
   bool IsFunctionConversion(QualType FromType, QualType ToType,
                             QualType &ResultTy);
   bool DiagnoseMultipleUserDefinedConversion(Expr *From, QualType ToType);
+  void DiagnoseUseOfDeletedFunction(SourceLocation Loc, SourceRange Range,
+                                    DeclarationName Name,
+                                    OverloadCandidateSet &CandidateSet,
+                                    FunctionDecl *Fn, MultiExprArg Args,
+                                    bool IsMember = false);
 
   ExprResult InitializeExplicitObjectArgument(Sema &S, Expr *Obj,
                                               FunctionDecl *Fun);

clang/lib/AST/ASTImporter.cpp

@@ -3947,6 +3947,14 @@ ExpectedDecl ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
     // decl and its redeclarations may be required.
   }
 
+  StringLiteral *Msg = D->getDeletedMessage();
+  if (Msg) {
+    auto Imported = import(Msg);
+    if (!Imported)
+      return Imported.takeError();
+    Msg = *Imported;
+  }
+
   ToFunction->setQualifierInfo(ToQualifierLoc);
   ToFunction->setAccess(D->getAccess());
   ToFunction->setLexicalDeclContext(LexicalDC);
@@ -3961,6 +3969,11 @@ ExpectedDecl ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
   ToFunction->setRangeEnd(ToEndLoc);
   ToFunction->setDefaultLoc(ToDefaultLoc);
 
+  if (Msg)
+    ToFunction->setDefaultedOrDeletedInfo(
+        FunctionDecl::DefaultedOrDeletedFunctionInfo::Create(
+            Importer.getToContext(), {}, Msg));
+
   // Set the parameters.
   for (auto *Param : Parameters) {
     Param->setOwningFunction(ToFunction);

clang/lib/AST/Decl.cpp

@@ -3058,7 +3058,7 @@ FunctionDecl::FunctionDecl(Kind DK, ASTContext &C, DeclContext *DC,
   FunctionDeclBits.IsTrivialForCall = false;
   FunctionDeclBits.IsDefaulted = false;
   FunctionDeclBits.IsExplicitlyDefaulted = false;
-  FunctionDeclBits.HasDefaultedFunctionInfo = false;
+  FunctionDeclBits.HasDefaultedOrDeletedInfo = false;
   FunctionDeclBits.IsIneligibleOrNotSelected = false;
   FunctionDeclBits.HasImplicitReturnZero = false;
   FunctionDeclBits.IsLateTemplateParsed = false;
@@ -3092,30 +3092,65 @@ bool FunctionDecl::isVariadic() const {
   return false;
 }
 
-FunctionDecl::DefaultedFunctionInfo *
-FunctionDecl::DefaultedFunctionInfo::Create(ASTContext &Context,
-                                            ArrayRef<DeclAccessPair> Lookups) {
-  DefaultedFunctionInfo *Info = new (Context.Allocate(
-      totalSizeToAlloc<DeclAccessPair>(Lookups.size()),
-      std::max(alignof(DefaultedFunctionInfo), alignof(DeclAccessPair))))
-      DefaultedFunctionInfo;
+FunctionDecl::DefaultedOrDeletedFunctionInfo *
+FunctionDecl::DefaultedOrDeletedFunctionInfo::Create(
+    ASTContext &Context, ArrayRef<DeclAccessPair> Lookups,
+    StringLiteral *DeletedMessage) {
+  static constexpr size_t Alignment =
+      std::max({alignof(DefaultedOrDeletedFunctionInfo),
+                alignof(DeclAccessPair), alignof(StringLiteral *)});
+  size_t Size = totalSizeToAlloc<DeclAccessPair, StringLiteral *>(
+      Lookups.size(), DeletedMessage != nullptr);
+
+  DefaultedOrDeletedFunctionInfo *Info =
+      new (Context.Allocate(Size, Alignment)) DefaultedOrDeletedFunctionInfo;
   Info->NumLookups = Lookups.size();
+  Info->HasDeletedMessage = DeletedMessage != nullptr;
+
   std::uninitialized_copy(Lookups.begin(), Lookups.end(),
                           Info->getTrailingObjects<DeclAccessPair>());
+  if (DeletedMessage)
+    *Info->getTrailingObjects<StringLiteral *>() = DeletedMessage;
   return Info;
 }
 
-void FunctionDecl::setDefaultedFunctionInfo(DefaultedFunctionInfo *Info) {
-  assert(!FunctionDeclBits.HasDefaultedFunctionInfo && "already have this");
+void FunctionDecl::setDefaultedOrDeletedInfo(
+    DefaultedOrDeletedFunctionInfo *Info) {
+  assert(!FunctionDeclBits.HasDefaultedOrDeletedInfo && "already have this");
   assert(!Body && "can't replace function body with defaulted function info");
 
-  FunctionDeclBits.HasDefaultedFunctionInfo = true;
-  DefaultedInfo = Info;
+  FunctionDeclBits.HasDefaultedOrDeletedInfo = true;
+  DefaultedOrDeletedInfo = Info;
+}
+
+void FunctionDecl::setDeletedAsWritten(bool D, StringLiteral *Message) {
+  FunctionDeclBits.IsDeleted = D;
+
+  if (Message) {
+    assert(isDeletedAsWritten() && "Function must be deleted");
+    if (FunctionDeclBits.HasDefaultedOrDeletedInfo)
+      DefaultedOrDeletedInfo->setDeletedMessage(Message);
+    else
+      setDefaultedOrDeletedInfo(DefaultedOrDeletedFunctionInfo::Create(
+          getASTContext(), /*Lookups=*/{}, Message));
+  }
+}
+
+void FunctionDecl::DefaultedOrDeletedFunctionInfo::setDeletedMessage(
+    StringLiteral *Message) {
+  // We should never get here with the DefaultedOrDeletedInfo populated, but
+  // no space allocated for the deleted message, since that would require
+  // recreating this, but setDefaultedOrDeletedInfo() disallows overwriting
+  // an already existing DefaultedOrDeletedFunctionInfo.
+  assert(HasDeletedMessage &&
+         "No space to store a delete message in this DefaultedOrDeletedInfo");
+  *getTrailingObjects<StringLiteral *>() = Message;
 }
 
-FunctionDecl::DefaultedFunctionInfo *
-FunctionDecl::getDefaultedFunctionInfo() const {
-  return FunctionDeclBits.HasDefaultedFunctionInfo ? DefaultedInfo : nullptr;
+FunctionDecl::DefaultedOrDeletedFunctionInfo *
+FunctionDecl::getDefalutedOrDeletedInfo() const {
+  return FunctionDeclBits.HasDefaultedOrDeletedInfo ? DefaultedOrDeletedInfo
+                                                    : nullptr;
 }
 
 bool FunctionDecl::hasBody(const FunctionDecl *&Definition) const {
@@ -3202,7 +3237,7 @@ Stmt *FunctionDecl::getBody(const FunctionDecl *&Definition) const {
   if (!hasBody(Definition))
     return nullptr;
 
-  assert(!Definition->FunctionDeclBits.HasDefaultedFunctionInfo &&
+  assert(!Definition->FunctionDeclBits.HasDefaultedOrDeletedInfo &&
          "definition should not have a body");
   if (Definition->Body)
     return Definition->Body.get(getASTContext().getExternalSource());
@@ -3211,7 +3246,7 @@ Stmt *FunctionDecl::getBody(const FunctionDecl *&Definition) const {
 }
 
 void FunctionDecl::setBody(Stmt *B) {
-  FunctionDeclBits.HasDefaultedFunctionInfo = false;
+  FunctionDeclBits.HasDefaultedOrDeletedInfo = false;
   Body = LazyDeclStmtPtr(B);
   if (B)
     EndRangeLoc = B->getEndLoc();