[Clang][Sema] Fix comparison of constraint expressions

This diff switches the approach to comparison of constraint expressions
to the new one based on template args substitution.
It continues the effort to fix our handling of out-of-line definitions
of constrained templates.

The associated GitHub issue: #61414

Test plan:
1/ ninja check-all
2/ bootstrapped Clang passes tests

Differential revision: https://reviews.llvm.org/D146178

Author: alexander-shaposhnikov

clang/lib/Sema/SemaConcept.cpp

@@ -260,6 +260,9 @@ calculateConstraintSatisfaction(Sema &S, const Expr *ConstraintExpr,
     return SubstitutedAtomicExpr;
   }
 
+  if (SubstitutedAtomicExpr.get()->isValueDependent())
+    return SubstitutedAtomicExpr;
+
   EnterExpressionEvaluationContext ConstantEvaluated(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
   SmallVector<PartialDiagnosticAt, 2> EvaluationDiags;
@@ -752,27 +755,43 @@ 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) {
-    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();
-    }
+    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;
   }
 
   llvm::FoldingSetNodeID ID1, ID2;

clang/lib/Sema/SemaOverload.cpp

@@ -1294,7 +1294,7 @@ 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->getTemplateParameters(),
+        NewTemplate, NewTemplate->getTemplateParameters(), OldTemplate,
         OldTemplate->getTemplateParameters(), false, TPL_TemplateMatch);
     bool SameReturnType = Context.hasSameType(Old->getDeclaredReturnType(),
                                               New->getDeclaredReturnType());

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -208,6 +208,10 @@ Response HandleFunction(const FunctionDecl *Function,
   return Response::UseNextDecl(Function);
 }
 
+Response HandleFunctionTemplateDecl(const FunctionTemplateDecl *FTD) {
+  return Response::ChangeDecl(FTD->getLexicalDeclContext());
+}
+
 Response HandleRecordDecl(const CXXRecordDecl *Rec,
                           MultiLevelTemplateArgumentList &Result,
                           ASTContext &Context,
@@ -318,6 +322,8 @@ 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);
     } else if (!isa<DeclContext>(CurDecl)) {
       R = Response::DontClearRelativeToPrimaryNextDecl(CurDecl);
       if (CurDecl->getDeclContext()->isTranslationUnit()) {

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -1653,33 +1653,12 @@ 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);
 
@@ -1689,16 +1668,37 @@ 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) {
-    if (PrevClassTemplate)
+    assert(!Owner->isDependentContext());
+    Inst->setLexicalDeclContext(Owner);
+    RecordInst->setLexicalDeclContext(Owner);
+
+    if (PrevClassTemplate) {
+      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;
+
       Inst->setAccess(PrevClassTemplate->getAccess());
-    else
+    } else {
       Inst->setAccess(D->getAccess());
+    }
 
     Inst->setObjectOfFriendDecl();
     // TODO: do we want to track the instantiation progeny of this
@@ -1709,15 +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-out-of-line-def.cpp

@@ -127,3 +127,153 @@ static_assert(S<XY>::specialization("str") == SPECIALIZATION_CONCEPT);
 static_assert(S<int>::specialization("str") == SPECIALIZATION_REQUIRES);
 
 } // namespace multiple_template_parameter_lists
+
+static constexpr int CONSTRAINED_METHOD_1 = 1;
+static constexpr int CONSTRAINED_METHOD_2 = 2;
+
+namespace constrained_members {
+
+template <int>
+struct S {
+  template <Concept C>
+  static constexpr int constrained_method();
+};
+
+template <>
+template <Concept C>
+constexpr int S<1>::constrained_method() { return CONSTRAINED_METHOD_1; }
+
+template <>
+template <Concept C>
+constexpr int S<2>::constrained_method() { return CONSTRAINED_METHOD_2; }
+
+static_assert(S<1>::constrained_method<XY>() == CONSTRAINED_METHOD_1);
+static_assert(S<2>::constrained_method<XY>() == CONSTRAINED_METHOD_2);
+
+
+template <class T1, class T2>
+concept ConceptT1T2 = true;
+
+template<typename T3>
+struct S12 {
+  template<ConceptT1T2<T3> T4>
+  static constexpr int constrained_method();
+};
+
+template<>
+template<ConceptT1T2<int> T5>
+constexpr int S12<int>::constrained_method() { return CONSTRAINED_METHOD_1; }
+
+template<>
+template<ConceptT1T2<double> T5>
+constexpr int S12<double>::constrained_method() { return CONSTRAINED_METHOD_2; }
+
+static_assert(S12<int>::constrained_method<XY>() == CONSTRAINED_METHOD_1);
+static_assert(S12<double>::constrained_method<XY>() == CONSTRAINED_METHOD_2);
+
+} // namespace constrained members
+
+namespace constrained_members_of_nested_types {
+
+template <int>
+struct S {
+  struct Inner0 {
+    struct Inner1 {
+      template <Concept C>
+      static constexpr int constrained_method();
+    };
+  };
+};
+
+template <>
+template <Concept C>
+constexpr int S<1>::Inner0::Inner1::constrained_method() { return CONSTRAINED_METHOD_1; }
+
+template <>
+template <Concept C>
+constexpr int S<2>::Inner0::Inner1::constrained_method() { return CONSTRAINED_METHOD_2; }
+
+static_assert(S<1>::Inner0::Inner1::constrained_method<XY>() == CONSTRAINED_METHOD_1);
+static_assert(S<2>::Inner0::Inner1::constrained_method<XY>() == CONSTRAINED_METHOD_2);
+
+
+template <class T1, class T2>
+concept ConceptT1T2 = true;
+
+template<typename T3>
+struct S12 {
+  struct Inner0 {
+    struct Inner1 {
+      template<ConceptT1T2<T3> T4>
+      static constexpr int constrained_method();
+    };
+  };
+};
+
+template<>
+template<ConceptT1T2<int> T5>
+constexpr int S12<int>::Inner0::Inner1::constrained_method() { return CONSTRAINED_METHOD_1; }
+
+template<>
+template<ConceptT1T2<double> T5>
+constexpr int S12<double>::Inner0::Inner1::constrained_method() { return CONSTRAINED_METHOD_2; }
+
+static_assert(S12<int>::Inner0::Inner1::constrained_method<XY>() == CONSTRAINED_METHOD_1);
+static_assert(S12<double>::Inner0::Inner1::constrained_method<XY>() == CONSTRAINED_METHOD_2);
+
+} // namespace constrained_members_of_nested_types
+
+namespace constrained_member_sfinae {
+
+template<int N> struct S {
+  template<class T>
+  static constexpr int constrained_method() requires (sizeof(int[N * 1073741824 + 4]) == 16) {
+    return CONSTRAINED_METHOD_1;
+  }
+
+  template<class T>
+  static constexpr int constrained_method() requires (sizeof(int[N]) == 16);
+};
+
+template<>
+template<typename T>
+constexpr int S<4>::constrained_method() requires (sizeof(int[4]) == 16) {
+  return CONSTRAINED_METHOD_2;
+}
+
+// Verify that there is no amiguity in this case.
+static_assert(S<4>::constrained_method<double>() == CONSTRAINED_METHOD_2);
+
+} // namespace constrained_member_sfinae
+
+namespace requires_expression_references_members {
+
+void accept1(int x);
+void accept2(XY xy);
+
+template <class T> struct S {
+  T Field = T();
+
+  constexpr int constrained_method()
+      requires requires { accept1(Field); };
+
+  constexpr int constrained_method()
+      requires requires { accept2(Field); };
+};
+
+template <class T>
+constexpr int S<T>::constrained_method()
+  requires requires { accept1(Field); } {
+  return CONSTRAINED_METHOD_1;
+}
+
+template <class T>
+constexpr int S<T>::constrained_method()
+  requires requires { accept2(Field); } {
+  return CONSTRAINED_METHOD_2;
+}
+
+static_assert(S<int>().constrained_method() == CONSTRAINED_METHOD_1);
+static_assert(S<XY>().constrained_method() == CONSTRAINED_METHOD_2);
+
+} // namespace requires_expression_references_members

clang/test/SemaTemplate/concepts.cpp

@@ -816,3 +816,12 @@ static_assert(Parent<int>::TakesBinary<int, 0>::i == 0);
 static_assert(Parent<int>::TakesBinary<int, 0ULL>::i == 0);
 }
 
+namespace TemplateInsideNonTemplateClass {
+template<typename T, typename U> concept C = true;
+
+template<typename T> auto L = []<C<T> U>() {};
+
+struct Q {
+  template<C<int> U> friend constexpr auto decltype(L<int>)::operator()() const;
+};
+} // namespace TemplateInsideNonTemplateClass

clang/www/cxx_status.html

@@ -947,9 +947,6 @@ <h2 id="cxx20">C++20 implementation status</h2>
       <tr>
         <td><a href="https://wg21.link/p1980r0">P1980R0</a></td>
       </tr>
-      <tr> <!-- from Prague -->
-        <td><a href="https://wg21.link/p2103r0">P2103R0</a></td>
-      </tr>
       <tr> <!-- from February 2022 -->
         <td><a href="https://wg21.link/p2493r0">P2493R0</a></td>
       </tr>
@@ -961,6 +958,9 @@ <h2 id="cxx20">C++20 implementation status</h2>
         <td><a href="https://wg21.link/p2113r0">P2113R0</a></td>
         <td rowspan="1" class="full" align="center">Clang 16</td>
       </tr>
+      <tr>
+        <td><a href="https://wg21.link/p2103r0">P2103R0</a></td>
+      </tr>
     <!-- Albuquerque papers -->
     <tr>
       <td>Range-based for statements with initializer</td>