Revert "[Clang] Implement CWG2369 "Ordering between constraints and substitution"" (llvm#122130)

Unfortunately that breaks some code on Windows when lambdas come into
play, as reported in
llvm#102857 (comment)

This reverts commit 96eced6.

Author: zyn0217

clang/include/clang/Sema/Sema.h

@@ -13062,7 +13062,6 @@ class Sema final : public SemaBase {
   ///
   /// \param SkipForSpecialization when specified, any template specializations
   /// in a traversal would be ignored.
-  ///
   /// \param ForDefaultArgumentSubstitution indicates we should continue looking
   /// when encountering a specialized member function template, rather than
   /// returning immediately.
@@ -13074,17 +13073,6 @@ class Sema final : public SemaBase {
       bool SkipForSpecialization = false,
       bool ForDefaultArgumentSubstitution = false);
 
-  /// Apart from storing the result to \p Result, this behaves the same as
-  /// another overload.
-  void getTemplateInstantiationArgs(
-      MultiLevelTemplateArgumentList &Result, const NamedDecl *D,
-      const DeclContext *DC = nullptr, bool Final = false,
-      std::optional<ArrayRef<TemplateArgument>> Innermost = std::nullopt,
-      bool RelativeToPrimary = false, const FunctionDecl *Pattern = nullptr,
-      bool ForConstraintInstantiation = false,
-      bool SkipForSpecialization = false,
-      bool ForDefaultArgumentSubstitution = false);
-
   /// RAII object to handle the state changes required to synthesize
   /// a function body.
   class SynthesizedFunctionScope {
@@ -13354,7 +13342,7 @@ class Sema final : public SemaBase {
   ExprResult
   SubstConstraintExpr(Expr *E,
                       const MultiLevelTemplateArgumentList &TemplateArgs);
-  // Unlike the above, this does not evaluate constraints.
+  // Unlike the above, this does not evaluates constraints.
   ExprResult SubstConstraintExprWithoutSatisfaction(
       Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs);
 
@@ -14475,10 +14463,10 @@ class Sema final : public SemaBase {
       const MultiLevelTemplateArgumentList &TemplateArgs,
       SourceRange TemplateIDRange);
 
-  bool CheckFunctionTemplateConstraints(SourceLocation PointOfInstantiation,
-                                        FunctionDecl *Decl,
-                                        ArrayRef<TemplateArgument> TemplateArgs,
-                                        ConstraintSatisfaction &Satisfaction);
+  bool CheckInstantiatedFunctionTemplateConstraints(
+      SourceLocation PointOfInstantiation, FunctionDecl *Decl,
+      ArrayRef<TemplateArgument> TemplateArgs,
+      ConstraintSatisfaction &Satisfaction);
 
   /// \brief Emit diagnostics explaining why a constraint expression was deemed
   /// unsatisfied.

clang/include/clang/Sema/Template.h

@@ -522,12 +522,6 @@ enum class TemplateSubstitutionKind : char {
     llvm::PointerUnion<Decl *, DeclArgumentPack *> *
     findInstantiationOf(const Decl *D);
 
-    /// Similar to \p findInstantiationOf(), but it wouldn't assert if the
-    /// instantiation was not found within the current instantiation scope. This
-    /// is helpful for on-demand declaration instantiation.
-    llvm::PointerUnion<Decl *, DeclArgumentPack *> *
-    findInstantiationUnsafe(const Decl *D);
-
     void InstantiatedLocal(const Decl *D, Decl *Inst);
     void InstantiatedLocalPackArg(const Decl *D, VarDecl *Inst);
     void MakeInstantiatedLocalArgPack(const Decl *D);

clang/lib/Sema/SemaConcept.cpp

@@ -846,7 +846,7 @@ bool Sema::CheckFunctionConstraints(const FunctionDecl *FD,
                                     bool ForOverloadResolution) {
   // Don't check constraints if the function is dependent. Also don't check if
   // this is a function template specialization, as the call to
-  // CheckFunctionTemplateConstraints after this will check it
+  // CheckinstantiatedFunctionTemplateConstraints after this will check it
   // better.
   if (FD->isDependentContext() ||
       FD->getTemplatedKind() ==
@@ -1111,55 +1111,12 @@ bool Sema::EnsureTemplateArgumentListConstraints(
   return false;
 }
 
-static bool CheckFunctionConstraintsWithoutInstantiation(
-    Sema &SemaRef, SourceLocation PointOfInstantiation,
-    FunctionTemplateDecl *Template, ArrayRef<TemplateArgument> TemplateArgs,
-    ConstraintSatisfaction &Satisfaction) {
-  SmallVector<const Expr *, 3> TemplateAC;
-  Template->getAssociatedConstraints(TemplateAC);
-  if (TemplateAC.empty()) {
-    Satisfaction.IsSatisfied = true;
-    return false;
-  }
-
-  LocalInstantiationScope Scope(SemaRef);
-
-  FunctionDecl *FD = Template->getTemplatedDecl();
-  // Collect the list of template arguments relative to the 'primary'
-  // template. We need the entire list, since the constraint is completely
-  // uninstantiated at this point.
-
-  // FIXME: Add TemplateArgs through the 'Innermost' parameter once
-  // the refactoring of getTemplateInstantiationArgs() relands.
-  MultiLevelTemplateArgumentList MLTAL;
-  MLTAL.addOuterTemplateArguments(Template, std::nullopt, /*Final=*/false);
-  SemaRef.getTemplateInstantiationArgs(
-      MLTAL, /*D=*/FD, FD,
-      /*Final=*/false, /*Innermost=*/std::nullopt, /*RelativeToPrimary=*/true,
-      /*Pattern=*/nullptr, /*ForConstraintInstantiation=*/true);
-  MLTAL.replaceInnermostTemplateArguments(Template, TemplateArgs);
-
-  Sema::ContextRAII SavedContext(SemaRef, FD);
-  std::optional<Sema::CXXThisScopeRAII> ThisScope;
-  if (auto *Method = dyn_cast<CXXMethodDecl>(FD))
-    ThisScope.emplace(SemaRef, /*Record=*/Method->getParent(),
-                      /*ThisQuals=*/Method->getMethodQualifiers());
-  return SemaRef.CheckConstraintSatisfaction(
-      Template, TemplateAC, MLTAL, PointOfInstantiation, Satisfaction);
-}
-
-bool Sema::CheckFunctionTemplateConstraints(
+bool Sema::CheckInstantiatedFunctionTemplateConstraints(
     SourceLocation PointOfInstantiation, FunctionDecl *Decl,
     ArrayRef<TemplateArgument> TemplateArgs,
     ConstraintSatisfaction &Satisfaction) {
   // In most cases we're not going to have constraints, so check for that first.
   FunctionTemplateDecl *Template = Decl->getPrimaryTemplate();
-
-  if (!Template)
-    return ::CheckFunctionConstraintsWithoutInstantiation(
-        *this, PointOfInstantiation, Decl->getDescribedFunctionTemplate(),
-        TemplateArgs, Satisfaction);
-
   // Note - code synthesis context for the constraints check is created
   // inside CheckConstraintsSatisfaction.
   SmallVector<const Expr *, 3> TemplateAC;

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -3936,6 +3936,18 @@ TemplateDeductionResult Sema::FinishTemplateArgumentDeduction(
       Result != TemplateDeductionResult::Success)
     return Result;
 
+  // C++ [temp.deduct.call]p10: [DR1391]
+  //   If deduction succeeds for all parameters that contain
+  //   template-parameters that participate in template argument deduction,
+  //   and all template arguments are explicitly specified, deduced, or
+  //   obtained from default template arguments, remaining parameters are then
+  //   compared with the corresponding arguments. For each remaining parameter
+  //   P with a type that was non-dependent before substitution of any
+  //   explicitly-specified template arguments, if the corresponding argument
+  //   A cannot be implicitly converted to P, deduction fails.
+  if (CheckNonDependent())
+    return TemplateDeductionResult::NonDependentConversionFailure;
+
   // Form the template argument list from the deduced template arguments.
   TemplateArgumentList *SugaredDeducedArgumentList =
       TemplateArgumentList::CreateCopy(Context, SugaredBuilder);
@@ -3965,39 +3977,6 @@ TemplateDeductionResult Sema::FinishTemplateArgumentDeduction(
     FD = const_cast<FunctionDecl *>(FDFriend);
     Owner = FD->getLexicalDeclContext();
   }
-  // C++20 [temp.deduct.general]p5: [CWG2369]
-  //   If the function template has associated constraints, those constraints
-  //   are checked for satisfaction. If the constraints are not satisfied, type
-  //   deduction fails.
-  //
-  // FIXME: We haven't implemented CWG2369 for lambdas yet, because we need
-  // to figure out how to instantiate lambda captures to the scope without
-  // first instantiating the lambda.
-  bool IsLambda = isLambdaCallOperator(FD) || isLambdaConversionOperator(FD);
-  if (!IsLambda && !IsIncomplete) {
-    if (CheckFunctionTemplateConstraints(
-            Info.getLocation(),
-            FunctionTemplate->getCanonicalDecl()->getTemplatedDecl(),
-            CanonicalBuilder, Info.AssociatedConstraintsSatisfaction))
-      return TemplateDeductionResult::MiscellaneousDeductionFailure;
-    if (!Info.AssociatedConstraintsSatisfaction.IsSatisfied) {
-      Info.reset(Info.takeSugared(),
-                 TemplateArgumentList::CreateCopy(Context, CanonicalBuilder));
-      return TemplateDeductionResult::ConstraintsNotSatisfied;
-    }
-  }
-  // C++ [temp.deduct.call]p10: [CWG1391]
-  //   If deduction succeeds for all parameters that contain
-  //   template-parameters that participate in template argument deduction,
-  //   and all template arguments are explicitly specified, deduced, or
-  //   obtained from default template arguments, remaining parameters are then
-  //   compared with the corresponding arguments. For each remaining parameter
-  //   P with a type that was non-dependent before substitution of any
-  //   explicitly-specified template arguments, if the corresponding argument
-  //   A cannot be implicitly converted to P, deduction fails.
-  if (CheckNonDependent())
-    return TemplateDeductionResult::NonDependentConversionFailure;
-
   MultiLevelTemplateArgumentList SubstArgs(
       FunctionTemplate, CanonicalDeducedArgumentList->asArray(),
       /*Final=*/false);
@@ -4032,8 +4011,8 @@ TemplateDeductionResult Sema::FinishTemplateArgumentDeduction(
   //   ([temp.constr.decl]), those constraints are checked for satisfaction
   //   ([temp.constr.constr]). If the constraints are not satisfied, type
   //   deduction fails.
-  if (IsLambda && !IsIncomplete) {
-    if (CheckFunctionTemplateConstraints(
+  if (!IsIncomplete) {
+    if (CheckInstantiatedFunctionTemplateConstraints(
             Info.getLocation(), Specialization, CanonicalBuilder,
             Info.AssociatedConstraintsSatisfaction))
       return TemplateDeductionResult::MiscellaneousDeductionFailure;

clang/lib/Sema/SemaTemplateDeductionGuide.cpp

@@ -902,12 +902,10 @@ Expr *buildIsDeducibleConstraint(Sema &SemaRef,
       Context.getTrivialTypeSourceInfo(
           Context.getDeducedTemplateSpecializationType(
               TemplateName(AliasTemplate), /*DeducedType=*/QualType(),
-              /*IsDependent=*/true),
-          AliasTemplate->getLocation()), // template specialization type whose
-                                         // arguments will be deduced.
+              /*IsDependent=*/true)), // template specialization type whose
+                                      // arguments will be deduced.
       Context.getTrivialTypeSourceInfo(
-          ReturnType, AliasTemplate->getLocation()), // type from which template
-                                                     // arguments are deduced.
+          ReturnType), // type from which template arguments are deduced.
   };
   return TypeTraitExpr::Create(
       Context, Context.getLogicalOperationType(), AliasTemplate->getLocation(),

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -475,21 +475,6 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
   assert((ND || DC) && "Can't find arguments for a decl if one isn't provided");
   // Accumulate the set of template argument lists in this structure.
   MultiLevelTemplateArgumentList Result;
-  getTemplateInstantiationArgs(
-      Result, ND, DC, Final, Innermost, RelativeToPrimary, Pattern,
-      ForConstraintInstantiation, SkipForSpecialization,
-      ForDefaultArgumentSubstitution);
-  return Result;
-}
-
-void Sema::getTemplateInstantiationArgs(
-    MultiLevelTemplateArgumentList &Result, const NamedDecl *ND,
-    const DeclContext *DC, bool Final,
-    std::optional<ArrayRef<TemplateArgument>> Innermost, bool RelativeToPrimary,
-    const FunctionDecl *Pattern, bool ForConstraintInstantiation,
-    bool SkipForSpecialization, bool ForDefaultArgumentSubstitution) {
-  assert((ND || DC) && "Can't find arguments for a decl if one isn't provided");
-  // Accumulate the set of template argument lists in this structure.
 
   using namespace TemplateInstArgsHelpers;
   const Decl *CurDecl = ND;
@@ -550,12 +535,14 @@ void Sema::getTemplateInstantiationArgs(
     }
 
     if (R.IsDone)
-      return;
+      return Result;
     if (R.ClearRelativeToPrimary)
       RelativeToPrimary = false;
     assert(R.NextDecl);
     CurDecl = R.NextDecl;
   }
+
+  return Result;
 }
 
 bool Sema::CodeSynthesisContext::isInstantiationRecord() const {
@@ -1362,19 +1349,6 @@ namespace {
     // Whether an incomplete substituion should be treated as an error.
     bool BailOutOnIncomplete;
 
-  private:
-    bool isSubstitutingConstraints() const {
-      return llvm::any_of(SemaRef.CodeSynthesisContexts, [](auto &Context) {
-        return Context.Kind ==
-               Sema::CodeSynthesisContext::ConstraintSubstitution;
-      });
-    }
-
-    // CWG2770: Function parameters should be instantiated when they are
-    // needed by a satisfaction check of an atomic constraint or
-    // (recursively) by another function parameter.
-    bool maybeInstantiateFunctionParameterToScope(ParmVarDecl *OldParm);
-
   public:
     typedef TreeTransform<TemplateInstantiator> inherited;
 
@@ -1431,19 +1405,12 @@ namespace {
                                  ArrayRef<UnexpandedParameterPack> Unexpanded,
                                  bool &ShouldExpand, bool &RetainExpansion,
                                  std::optional<unsigned> &NumExpansions) {
-      if (SemaRef.CurrentInstantiationScope && isSubstitutingConstraints()) {
-        for (UnexpandedParameterPack ParmPack : Unexpanded) {
-          NamedDecl *VD = ParmPack.first.dyn_cast<NamedDecl *>();
-          if (!isa_and_present<ParmVarDecl>(VD))
-            continue;
-          if (maybeInstantiateFunctionParameterToScope(cast<ParmVarDecl>(VD)))
-            return true;
-        }
-      }
-
-      return getSema().CheckParameterPacksForExpansion(
-          EllipsisLoc, PatternRange, Unexpanded, TemplateArgs, ShouldExpand,
-          RetainExpansion, NumExpansions);
+      return getSema().CheckParameterPacksForExpansion(EllipsisLoc,
+                                                       PatternRange, Unexpanded,
+                                                       TemplateArgs,
+                                                       ShouldExpand,
+                                                       RetainExpansion,
+                                                       NumExpansions);
     }
 
     void ExpandingFunctionParameterPack(ParmVarDecl *Pack) {
@@ -1944,62 +1911,9 @@ Decl *TemplateInstantiator::TransformDecl(SourceLocation Loc, Decl *D) {
     // template parameter.
   }
 
-  if (SemaRef.CurrentInstantiationScope) {
-    if (isSubstitutingConstraints() && isa<ParmVarDecl>(D) &&
-        maybeInstantiateFunctionParameterToScope(cast<ParmVarDecl>(D)))
-      return nullptr;
-  }
-
   return SemaRef.FindInstantiatedDecl(Loc, cast<NamedDecl>(D), TemplateArgs);
 }
 
-bool TemplateInstantiator::maybeInstantiateFunctionParameterToScope(
-    ParmVarDecl *OldParm) {
-  if (SemaRef.CurrentInstantiationScope->findInstantiationUnsafe(OldParm))
-    return false;
-  // We're instantiating a function parameter whose associated function template
-  // has not been instantiated at this point for constraint evaluation, so make
-  // sure the instantiated parameters are owned by a function declaration such
-  // that they can be correctly 'captured' in tryCaptureVariable().
-  Sema::ContextRAII Context(SemaRef, OldParm->getDeclContext());
-
-  if (!OldParm->isParameterPack())
-    return !TransformFunctionTypeParam(OldParm, /*indexAdjustment=*/0,
-                                       /*NumExpansions=*/std::nullopt,
-                                       /*ExpectParameterPack=*/false);
-
-  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
-
-  // Find the parameter packs that could be expanded.
-  TypeLoc TL = OldParm->getTypeSourceInfo()->getTypeLoc();
-  PackExpansionTypeLoc ExpansionTL = TL.castAs<PackExpansionTypeLoc>();
-  TypeLoc Pattern = ExpansionTL.getPatternLoc();
-  SemaRef.collectUnexpandedParameterPacks(Pattern, Unexpanded);
-  assert(!Unexpanded.empty() && "Pack expansion without parameter packs?");
-
-  bool ShouldExpand = false;
-  bool RetainExpansion = false;
-  std::optional<unsigned> OrigNumExpansions =
-      ExpansionTL.getTypePtr()->getNumExpansions();
-  std::optional<unsigned> NumExpansions = OrigNumExpansions;
-  if (TryExpandParameterPacks(ExpansionTL.getEllipsisLoc(),
-                              Pattern.getSourceRange(), Unexpanded,
-                              ShouldExpand, RetainExpansion, NumExpansions))
-    return true;
-
-  assert(ShouldExpand && !RetainExpansion &&
-         "Shouldn't preserve pack expansion when evaluating constraints");
-  ExpandingFunctionParameterPack(OldParm);
-  for (unsigned I = 0; I != *NumExpansions; ++I) {
-    Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(getSema(), I);
-    if (!TransformFunctionTypeParam(OldParm, /*indexAdjustment=*/0,
-                                    /*NumExpansions=*/OrigNumExpansions,
-                                    /*ExpectParameterPack=*/false))
-      return true;
-  }
-  return false;
-}
-
 Decl *TemplateInstantiator::TransformDefinition(SourceLocation Loc, Decl *D) {
   Decl *Inst = getSema().SubstDecl(D, getSema().CurContext, TemplateArgs);
   if (!Inst)
@@ -4677,8 +4591,9 @@ static const Decl *getCanonicalParmVarDecl(const Decl *D) {
   return D;
 }
 
+
 llvm::PointerUnion<Decl *, LocalInstantiationScope::DeclArgumentPack *> *
-LocalInstantiationScope::findInstantiationUnsafe(const Decl *D) {
+LocalInstantiationScope::findInstantiationOf(const Decl *D) {
   D = getCanonicalParmVarDecl(D);
   for (LocalInstantiationScope *Current = this; Current;
        Current = Current->Outer) {
@@ -4703,14 +4618,6 @@ LocalInstantiationScope::findInstantiationUnsafe(const Decl *D) {
       break;
   }
 
-  return nullptr;
-}
-
-llvm::PointerUnion<Decl *, LocalInstantiationScope::DeclArgumentPack *> *
-LocalInstantiationScope::findInstantiationOf(const Decl *D) {
-  auto *Result = findInstantiationUnsafe(D);
-  if (Result)
-    return Result;
   // If we're performing a partial substitution during template argument
   // deduction, we may not have values for template parameters yet.
   if (isa<NonTypeTemplateParmDecl>(D) || isa<TemplateTypeParmDecl>(D) ||

clang/lib/Sema/TreeTransform.h

@@ -713,7 +713,7 @@ class TreeTransform {
   /// variables vector are acceptable.
   ///
   /// LastParamTransformed, if non-null, will be set to the index of the last
-  /// parameter on which transformation was started. In the event of an error,
+  /// parameter on which transfromation was started. In the event of an error,
   /// this will contain the parameter which failed to instantiate.
   ///
   /// Return true on error.