Revert "[Clang][Sema] Fix comparison of constraint expressions"

This reverts commit e3b1083.

This was reverted because it breaks a number of libstdc++ examples, AND
required a workaround that causes hiding of legitimate bugs.

clang/include/clang/AST/DeclTemplate.h

@@ -2309,15 +2309,9 @@ class ClassTemplateDecl : public RedeclarableTemplateDecl {
     return static_cast<Common *>(RedeclarableTemplateDecl::getCommonPtr());
   }
 
-  void setCommonPtr(Common *C) {
-    RedeclarableTemplateDecl::Common = C;
-  }
-
 public:
-
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
-  friend class TemplateDeclInstantiator;
 
   /// Load any lazily-loaded specializations from the external source.
   void LoadLazySpecializations() const;

clang/include/clang/Sema/Template.h

@@ -232,21 +232,9 @@ enum class TemplateSubstitutionKind : char {
     /// Replaces the current 'innermost' level with the provided argument list.
     /// This is useful for type deduction cases where we need to get the entire
     /// list from the AST, but then add the deduced innermost list.
-    void replaceInnermostTemplateArguments(Decl *AssociatedDecl, ArgList Args) {
-      assert((!TemplateArgumentLists.empty() || NumRetainedOuterLevels) &&
-             "Replacing in an empty list?");
-
-      if (!TemplateArgumentLists.empty()) {
-        assert((TemplateArgumentLists[0].AssociatedDeclAndFinal.getPointer() ||
-                TemplateArgumentLists[0].AssociatedDeclAndFinal.getPointer() ==
-                    AssociatedDecl) &&
-               "Trying to change incorrect declaration?");
-        TemplateArgumentLists[0].Args = Args;
-      } else {
-        --NumRetainedOuterLevels;
-        TemplateArgumentLists.push_back(
-            {{AssociatedDecl, /*Final=*/false}, Args});
-      }
+    void replaceInnermostTemplateArguments(ArgList Args) {
+      assert(TemplateArgumentLists.size() > 0 && "Replacing in an empty list?");
+      TemplateArgumentLists[0].Args = Args;
     }
 
     /// Add an outermost level that we are not substituting. We have no

clang/lib/Sema/SemaConcept.cpp

@@ -721,7 +721,7 @@ CalculateTemplateDepthForConstraints(Sema &S, const NamedDecl *ND,
       ND, /*Final=*/false, /*Innermost=*/nullptr, /*RelativeToPrimary=*/true,
       /*Pattern=*/nullptr,
       /*ForConstraintInstantiation=*/true, SkipForSpecialization);
-  return MLTAL.getNumLevels();
+  return MLTAL.getNumSubstitutedLevels();
 }
 
 namespace {
@@ -752,44 +752,27 @@ namespace {
   };
 } // namespace
 
-static const Expr *SubstituteConstraintExpression(Sema &S, const NamedDecl *ND,
-                                                  const Expr *ConstrExpr) {
-  MultiLevelTemplateArgumentList MLTAL = S.getTemplateInstantiationArgs(
-      ND, /*Final=*/false, /*Innermost=*/nullptr,
-      /*RelativeToPrimary=*/true,
-      /*Pattern=*/nullptr, /*ForConstraintInstantiation=*/true,
-      /*SkipForSpecialization*/ false);
-  if (MLTAL.getNumSubstitutedLevels() == 0)
-    return ConstrExpr;
-
-  Sema::SFINAETrap SFINAE(S, /*AccessCheckingSFINAE=*/false);
-  std::optional<Sema::CXXThisScopeRAII> ThisScope;
-  if (auto *RD = dyn_cast<CXXRecordDecl>(ND->getDeclContext()))
-    ThisScope.emplace(S, const_cast<CXXRecordDecl *>(RD), Qualifiers());
-  ExprResult SubstConstr =
-      S.SubstConstraintExpr(const_cast<clang::Expr *>(ConstrExpr), MLTAL);
-  if (SFINAE.hasErrorOccurred() || !SubstConstr.isUsable())
-    return nullptr;
-  return SubstConstr.get();
-}
-
 bool Sema::AreConstraintExpressionsEqual(const NamedDecl *Old,
                                          const Expr *OldConstr,
                                          const NamedDecl *New,
                                          const Expr *NewConstr) {
-  if (OldConstr == NewConstr)
-    return true;
   if (Old && New && Old != New) {
-    if (const Expr *SubstConstr =
-            SubstituteConstraintExpression(*this, Old, OldConstr))
-      OldConstr = SubstConstr;
-    else
-      return false;
-    if (const Expr *SubstConstr =
-            SubstituteConstraintExpression(*this, New, NewConstr))
-      NewConstr = SubstConstr;
-    else
-      return false;
+    unsigned Depth1 = CalculateTemplateDepthForConstraints(
+        *this, Old);
+    unsigned Depth2 = CalculateTemplateDepthForConstraints(
+        *this, New);
+
+    // Adjust the 'shallowest' verison of this to increase the depth to match
+    // the 'other'.
+    if (Depth2 > Depth1) {
+      OldConstr = AdjustConstraintDepth(*this, Depth2 - Depth1)
+                      .TransformExpr(const_cast<Expr *>(OldConstr))
+                      .get();
+    } else if (Depth1 > Depth2) {
+      NewConstr = AdjustConstraintDepth(*this, Depth1 - Depth2)
+                      .TransformExpr(const_cast<Expr *>(NewConstr))
+                      .get();
+    }
   }
 
   llvm::FoldingSetNodeID ID1, ID2;

clang/lib/Sema/SemaOverload.cpp

@@ -1296,7 +1296,7 @@ bool Sema::IsOverload(FunctionDecl *New, FunctionDecl *Old,
     // We check the return type and template parameter lists for function
     // templates first; the remaining checks follow.
     bool SameTemplateParameterList = TemplateParameterListsAreEqual(
-        NewTemplate, NewTemplate->getTemplateParameters(), OldTemplate,
+        NewTemplate->getTemplateParameters(),
         OldTemplate->getTemplateParameters(), false, TPL_TemplateMatch);
     bool SameReturnType = Context.hasSameType(Old->getDeclaredReturnType(),
                                               New->getDeclaredReturnType());

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -2881,7 +2881,7 @@ CheckDeducedArgumentConstraints(Sema &S, TemplateDeclT *Template,
   // not class-scope explicit specialization, so replace with Deduced Args
   // instead of adding to inner-most.
   if (NeedsReplacement)
-    MLTAL.replaceInnermostTemplateArguments(Template, CanonicalDeducedArgs);
+    MLTAL.replaceInnermostTemplateArguments(CanonicalDeducedArgs);
 
   if (S.CheckConstraintSatisfaction(Template, AssociatedConstraints, MLTAL,
                                     Info.getLocation(),

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -131,14 +131,6 @@ HandleDefaultTempArgIntoTempTempParam(const TemplateTemplateParmDecl *TTP,
   return Response::Done();
 }
 
-Response HandlePartialClassTemplateSpec(
-    const ClassTemplatePartialSpecializationDecl *PartialClassTemplSpec,
-    MultiLevelTemplateArgumentList &Result, bool SkipForSpecialization) {
-  if (!SkipForSpecialization)
-      Result.addOuterRetainedLevels(PartialClassTemplSpec->getTemplateDepth());
-  return Response::Done();
-}
-
 // Add template arguments from a class template instantiation.
 Response
 HandleClassTemplateSpec(const ClassTemplateSpecializationDecl *ClassTemplSpec,
@@ -216,21 +208,6 @@ Response HandleFunction(const FunctionDecl *Function,
   return Response::UseNextDecl(Function);
 }
 
-Response HandleFunctionTemplateDecl(const FunctionTemplateDecl *FTD,
-                                    MultiLevelTemplateArgumentList &Result) {
-  if (!isa<ClassTemplateSpecializationDecl>(FTD->getDeclContext())) {
-    NestedNameSpecifier *NNS = FTD->getTemplatedDecl()->getQualifier();
-    const Type *Ty;
-    const TemplateSpecializationType *TSTy;
-    if (NNS && (Ty = NNS->getAsType()) &&
-        (TSTy = Ty->getAs<TemplateSpecializationType>()))
-      Result.addOuterTemplateArguments(const_cast<FunctionTemplateDecl *>(FTD),
-                                       TSTy->template_arguments(),
-                                       /*Final=*/false);
-  }
-  return Response::ChangeDecl(FTD->getLexicalDeclContext());
-}
-
 Response HandleRecordDecl(const CXXRecordDecl *Rec,
                           MultiLevelTemplateArgumentList &Result,
                           ASTContext &Context,
@@ -241,10 +218,15 @@ Response HandleRecordDecl(const CXXRecordDecl *Rec,
         "Outer template not instantiated?");
     if (ClassTemplate->isMemberSpecialization())
       return Response::Done();
-    if (ForConstraintInstantiation)
+    if (ForConstraintInstantiation) {
+      QualType RecordType = Context.getTypeDeclType(Rec);
+      QualType Injected = cast<InjectedClassNameType>(RecordType)
+                              ->getInjectedSpecializationType();
+      const auto *InjectedType = cast<TemplateSpecializationType>(Injected);
       Result.addOuterTemplateArguments(const_cast<CXXRecordDecl *>(Rec),
-                                       ClassTemplate->getInjectedTemplateArgs(),
+                                       InjectedType->template_arguments(),
                                        /*Final=*/false);
+    }
   }
 
   bool IsFriend = Rec->getFriendObjectKind() ||
@@ -324,10 +306,6 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
     if (const auto *VarTemplSpec =
             dyn_cast<VarTemplateSpecializationDecl>(CurDecl)) {
       R = HandleVarTemplateSpec(VarTemplSpec, Result, SkipForSpecialization);
-    } else if (const auto *PartialClassTemplSpec =
-                   dyn_cast<ClassTemplatePartialSpecializationDecl>(CurDecl)) {
-      R = HandlePartialClassTemplateSpec(PartialClassTemplSpec, Result,
-                                         SkipForSpecialization);
     } else if (const auto *ClassTemplSpec =
                    dyn_cast<ClassTemplateSpecializationDecl>(CurDecl)) {
       R = HandleClassTemplateSpec(ClassTemplSpec, Result,
@@ -340,8 +318,6 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
     } else if (const auto *CSD =
                    dyn_cast<ImplicitConceptSpecializationDecl>(CurDecl)) {
       R = HandleImplicitConceptSpecializationDecl(CSD, Result);
-    } else if (const auto *FTD = dyn_cast<FunctionTemplateDecl>(CurDecl)) {
-      R = HandleFunctionTemplateDecl(FTD, Result);
     } else if (!isa<DeclContext>(CurDecl)) {
       R = Response::DontClearRelativeToPrimaryNextDecl(CurDecl);
       if (CurDecl->getDeclContext()->isTranslationUnit()) {

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -1653,12 +1653,33 @@ Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
         << QualifierLoc.getSourceRange();
       return nullptr;
     }
+
+    if (PrevClassTemplate) {
+      const ClassTemplateDecl *MostRecentPrevCT =
+          PrevClassTemplate->getMostRecentDecl();
+      TemplateParameterList *PrevParams =
+          MostRecentPrevCT->getTemplateParameters();
+
+      // Make sure the parameter lists match.
+      if (!SemaRef.TemplateParameterListsAreEqual(
+              D->getTemplatedDecl(), InstParams,
+              MostRecentPrevCT->getTemplatedDecl(), PrevParams, true,
+              Sema::TPL_TemplateMatch))
+        return nullptr;
+
+      // Do some additional validation, then merge default arguments
+      // from the existing declarations.
+      if (SemaRef.CheckTemplateParameterList(InstParams, PrevParams,
+                                             Sema::TPC_ClassTemplate))
+        return nullptr;
+    }
   }
 
   CXXRecordDecl *RecordInst = CXXRecordDecl::Create(
       SemaRef.Context, Pattern->getTagKind(), DC, Pattern->getBeginLoc(),
       Pattern->getLocation(), Pattern->getIdentifier(), PrevDecl,
       /*DelayTypeCreation=*/true);
+
   if (QualifierLoc)
     RecordInst->setQualifierInfo(QualifierLoc);
 
@@ -1668,38 +1689,16 @@ Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
   ClassTemplateDecl *Inst
     = ClassTemplateDecl::Create(SemaRef.Context, DC, D->getLocation(),
                                 D->getIdentifier(), InstParams, RecordInst);
+  assert(!(isFriend && Owner->isDependentContext()));
+  Inst->setPreviousDecl(PrevClassTemplate);
+
   RecordInst->setDescribedClassTemplate(Inst);
 
   if (isFriend) {
-    assert(!Owner->isDependentContext());
-    Inst->setLexicalDeclContext(Owner);
-    RecordInst->setLexicalDeclContext(Owner);
-
-    if (PrevClassTemplate) {
-      Inst->setCommonPtr(PrevClassTemplate->getCommonPtr());
-      RecordInst->setTypeForDecl(
-          PrevClassTemplate->getTemplatedDecl()->getTypeForDecl());
-      const ClassTemplateDecl *MostRecentPrevCT =
-          PrevClassTemplate->getMostRecentDecl();
-      TemplateParameterList *PrevParams =
-          MostRecentPrevCT->getTemplateParameters();
-
-      // Make sure the parameter lists match.
-      if (!SemaRef.TemplateParameterListsAreEqual(
-              RecordInst, InstParams, MostRecentPrevCT->getTemplatedDecl(),
-              PrevParams, true, Sema::TPL_TemplateMatch))
-        return nullptr;
-
-      // Do some additional validation, then merge default arguments
-      // from the existing declarations.
-      if (SemaRef.CheckTemplateParameterList(InstParams, PrevParams,
-                                             Sema::TPC_ClassTemplate))
-        return nullptr;
-
+    if (PrevClassTemplate)
       Inst->setAccess(PrevClassTemplate->getAccess());
-    } else {
+    else
       Inst->setAccess(D->getAccess());
-    }
 
     Inst->setObjectOfFriendDecl();
     // TODO: do we want to track the instantiation progeny of this
@@ -1710,15 +1709,15 @@ Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
       Inst->setInstantiatedFromMemberTemplate(D);
   }
 
-  Inst->setPreviousDecl(PrevClassTemplate);
-
   // Trigger creation of the type for the instantiation.
-  SemaRef.Context.getInjectedClassNameType(
-      RecordInst, Inst->getInjectedClassNameSpecialization());
+  SemaRef.Context.getInjectedClassNameType(RecordInst,
+                                    Inst->getInjectedClassNameSpecialization());
 
   // Finish handling of friends.
   if (isFriend) {
     DC->makeDeclVisibleInContext(Inst);
+    Inst->setLexicalDeclContext(Owner);
+    RecordInst->setLexicalDeclContext(Owner);
     return Inst;
   }
 

clang/test/SemaTemplate/concepts-friends.cpp

@@ -441,27 +441,3 @@ namespace NTTP {
     templ_func<1>(u2);
   }
 }
-
-
-namespace FrineOfFriend {
-
-template <typename>
-concept Concept = true;
-
-template <Concept> class FriendOfBar;
-
-template <Concept> class Bar {
-  template <Concept> friend class FriendOfBar;
-};
-
-Bar<void> BarInstance;
-
-namespace internal {
-void FriendOfFoo(FriendOfBar<void>);
-}
-
-template <Concept> class Foo {
-  friend void internal::FriendOfFoo(FriendOfBar<void>);
-};
-
-} // namespace FrineOfFriend