Fix unexpected nullptr in ConceptSpecializationExpr's ArgsAsWritten field

[yeswalrus]

Summary

Fix ArgsAsWritten being null for ConceptSpecializationExpr in certain circumstances when parsing ASTs

ASTStmtWriter::VisitConceptSpecializationExpr expects getTemplateArgsAsWritten() to return a real value, which it wasn't when parsed by ASTContext.cpp in certain edge cases.

Resubmitting https://reviews.llvm.org/differential/revision/edit/146678/ rebased on the llvm-16.0.0 branch.

[yeswalrus]

Resolves https://github.com/llvm/llvm-project/issues/61486, Similar to https://reviews.llvm.org/D146678 but targeting the llvm-16 series.

[yeswalrus]

Hoping this can make it into clang-16.0.1, since the crash this causes makes clangd unusable in codebases using concepts in template arguments in this manner.

clang/include/clang/AST/ExprConcepts.h

ConceptSpecializationExpr(const ASTContext &C, NestedNameSpecifierLoc NNS,
                             SourceLocation TemplateKWLoc,
                             DeclarationNameInfo ConceptNameInfo,
                             NamedDecl *FoundDecl, ConceptDecl *NamedConcept,
                             const ASTTemplateArgumentListInfo *ArgsAsWritten,
                             ImplicitConceptSpecializationDecl *SpecDecl,
                             const ConstraintSatisfaction *Satisfaction);
 
   ConceptSpecializationExpr(const ASTContext &C, ConceptDecl *NamedConcept,
+                            const ASTTemplateArgumentListInfo *ArgsAsWritten,
                             ImplicitConceptSpecializationDecl *SpecDecl,
                             const ConstraintSatisfaction *Satisfaction,
                             bool Dependent,
                             bool ContainsUnexpandedParameterPack);
   ConceptSpecializationExpr(EmptyShell Empty);
 
 public:
   static ConceptSpecializationExpr *
   Create(const ASTContext &C, NestedNameSpecifierLoc NNS,
          SourceLocation TemplateKWLoc, DeclarationNameInfo ConceptNameInfo,
          NamedDecl *FoundDecl, ConceptDecl *NamedConcept,
          const ASTTemplateArgumentListInfo *ArgsAsWritten,
          ImplicitConceptSpecializationDecl *SpecDecl,
          const ConstraintSatisfaction *Satisfaction);
 
   static ConceptSpecializationExpr *
   Create(const ASTContext &C, ConceptDecl *NamedConcept,
+         const ASTTemplateArgumentListInfo *ArgsAsWritten,
          ImplicitConceptSpecializationDecl *SpecDecl,
          const ConstraintSatisfaction *Satisfaction, bool Dependent,
          bool ContainsUnexpandedParameterPack);
 
   ArrayRef<TemplateArgument> getTemplateArguments() const {
     return SpecDecl->getTemplateArguments();
   }
 

clang/lib/AST/ASTContext.cpp

if (OldConverted.front().getKind() == TemplateArgument::Pack) {
     NewConverted.push_back(ConstrainedType);
     llvm::append_range(NewConverted, OldConverted.drop_front(1));
   }
   auto *CSD = ImplicitConceptSpecializationDecl::Create(
       C, CSE->getNamedConcept()->getDeclContext(),
       CSE->getNamedConcept()->getLocation(), NewConverted);
 
   Expr *NewIDC = ConceptSpecializationExpr::Create(
-      C, CSE->getNamedConcept(), CSD, nullptr, CSE->isInstantiationDependent(),
-      CSE->containsUnexpandedParameterPack());
+      C, CSE->getNamedConcept(), CSE->getTemplateArgsAsWritten(), CSD, nullptr,
+      CSE->isInstantiationDependent(), CSE->containsUnexpandedParameterPack());
 
   if (auto *OrigFold = dyn_cast<CXXFoldExpr>(IDC))
     NewIDC = new (C) CXXFoldExpr(
         OrigFold->getType(), /*Callee*/ nullptr, SourceLocation(), NewIDC,
         BinaryOperatorKind::BO_LAnd, SourceLocation(), /*RHS=*/nullptr,
         SourceLocation(), /*NumExpansions=*/std::nullopt);
   return NewIDC;
 }

clang/lib/AST/ExprConcepts.cpp

ConceptSpecializationExpr *ConceptSpecializationExpr::Create(
     const ConstraintSatisfaction *Satisfaction) {
   return new (C) ConceptSpecializationExpr(
       C, NNS, TemplateKWLoc, ConceptNameInfo, FoundDecl, NamedConcept,
       ArgsAsWritten, SpecDecl, Satisfaction);
 }
 
 ConceptSpecializationExpr::ConceptSpecializationExpr(
     const ASTContext &C, ConceptDecl *NamedConcept,
+    const ASTTemplateArgumentListInfo *ArgsAsWritten,
     ImplicitConceptSpecializationDecl *SpecDecl,
     const ConstraintSatisfaction *Satisfaction, bool Dependent,
     bool ContainsUnexpandedParameterPack)
     : Expr(ConceptSpecializationExprClass, C.BoolTy, VK_PRValue, OK_Ordinary),
       ConceptReference(NestedNameSpecifierLoc(), SourceLocation(),
                        DeclarationNameInfo(), NamedConcept, NamedConcept,
-                       nullptr),
+                       ArgsAsWritten),
       SpecDecl(SpecDecl),
       Satisfaction(Satisfaction
                        ? ASTConstraintSatisfaction::Create(C, *Satisfaction)
                        : nullptr) {
   ExprDependence D = ExprDependence::None;
   if (!Satisfaction)
     D |= ExprDependence::Value;
   if (Dependent)
     D |= ExprDependence::Instantiation;
   if (ContainsUnexpandedParameterPack)
     D |= ExprDependence::UnexpandedPack;
   setDependence(D);
 }
 
 ConceptSpecializationExpr *ConceptSpecializationExpr::Create(
     const ASTContext &C, ConceptDecl *NamedConcept,
+    const ASTTemplateArgumentListInfo *ArgsAsWritten,
     ImplicitConceptSpecializationDecl *SpecDecl,
     const ConstraintSatisfaction *Satisfaction, bool Dependent,
     bool ContainsUnexpandedParameterPack) {
-  return new (C)
-      ConceptSpecializationExpr(C, NamedConcept, SpecDecl, Satisfaction,
-                                Dependent, ContainsUnexpandedParameterPack);
+  return new (C) ConceptSpecializationExpr(C, NamedConcept, ArgsAsWritten,
+                                           SpecDecl, Satisfaction, Dependent,
+                                           ContainsUnexpandedParameterPack);
 }
 
 const TypeConstraint *
 concepts::ExprRequirement::ReturnTypeRequirement::getTypeConstraint() const {
   assert(isTypeConstraint());
   auto TPL =
       TypeConstraintInfo.getPointer().get<TemplateParameterList *>();
   return cast<TemplateTypeParmDecl>(TPL->getParam(0))

clang/test/PCH/cxx2a-constraints.cpp

 template <SizedLike<int> T> void h(T) {}
 template <SizedLike<char> T> void h(T) {}
 
 template <SizedLike<int> T> void i(T) {}
 template <SizedLike T> void i(T) {}
 
 void j(SizedLike<int> auto ...ints) {}
 
+template<template<SizedLike> class P> struct S1 { };
+
 #else /*included pch*/
 
 int main() {
   (void)f('1');
   (void)f(1);
   (void)g('1');
   (void)g(1);
   (void)h('1');
   (void)h(1);
   (void)i('1');
   (void)i(1);
   (void)j(1, 2, 3);
 }
 
 #endif // HEADER