PR31606: Generalize our tentative DR resolution for inheriting copy/move

constructors to better match the pre-P0136R1 behavior.

llvm-svn: 291955

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -3344,8 +3344,8 @@ def note_ovl_candidate : Note<"candidate "
 def note_ovl_candidate_inherited_constructor : Note<
     "constructor from base class %0 inherited here">;
 def note_ovl_candidate_inherited_constructor_slice : Note<
-    "constructor inherited from base class cannot be used to initialize from "
-    "an argument of the derived class type">;
+    "candidate %select{constructor|template}0 ignored: "
+    "inherited constructor cannot be used to %select{copy|move}1 object">;
 def note_ovl_candidate_illegal_constructor : Note<
     "candidate %select{constructor|template}0 ignored: "
     "instantiation %select{takes|would take}0 its own class type by value">;

clang/lib/Sema/SemaOverload.cpp

@@ -5944,6 +5944,28 @@ Sema::AddOverloadCandidate(FunctionDecl *Function,
       Candidate.FailureKind = ovl_fail_illegal_constructor;
       return;
     }
+
+    // C++ [over.match.funcs]p8: (proposed DR resolution)
+    //   A constructor inherited from class type C that has a first parameter
+    //   of type "reference to P" (including such a constructor instantiated
+    //   from a template) is excluded from the set of candidate functions when
+    //   constructing an object of type cv D if the argument list has exactly
+    //   one argument and D is reference-related to P and P is reference-related
+    //   to C.
+    auto *Shadow = dyn_cast<ConstructorUsingShadowDecl>(FoundDecl.getDecl());
+    if (Shadow && Args.size() == 1 && Constructor->getNumParams() >= 1 &&
+        Constructor->getParamDecl(0)->getType()->isReferenceType()) {
+      QualType P = Constructor->getParamDecl(0)->getType()->getPointeeType();
+      QualType C = Context.getRecordType(Constructor->getParent());
+      QualType D = Context.getRecordType(Shadow->getParent());
+      SourceLocation Loc = Args.front()->getExprLoc();
+      if ((Context.hasSameUnqualifiedType(P, C) || IsDerivedFrom(Loc, P, C)) &&
+          (Context.hasSameUnqualifiedType(D, P) || IsDerivedFrom(Loc, D, P))) {
+        Candidate.Viable = false;
+        Candidate.FailureKind = ovl_fail_inhctor_slice;
+        return;
+      }
+    }
   }
 
   unsigned NumParams = Proto->getNumParams();
@@ -6016,31 +6038,6 @@ Sema::AddOverloadCandidate(FunctionDecl *Function,
     }
   }
 
-  // C++ [over.best.ics]p4+: (proposed DR resolution)
-  //   If the target is the first parameter of an inherited constructor when
-  //   constructing an object of type C with an argument list that has exactly
-  //   one expression, an implicit conversion sequence cannot be formed if C is
-  //   reference-related to the type that the argument would have after the
-  //   application of the user-defined conversion (if any) and before the final
-  //   standard conversion sequence. 
-  auto *Shadow = dyn_cast<ConstructorUsingShadowDecl>(FoundDecl.getDecl());
-  if (Shadow && Args.size() == 1 && !isa<InitListExpr>(Args.front())) {
-    bool DerivedToBase, ObjCConversion, ObjCLifetimeConversion;
-    QualType ConvertedArgumentType = Args.front()->getType();
-    if (Candidate.Conversions[0].isUserDefined())
-      ConvertedArgumentType =
-          Candidate.Conversions[0].UserDefined.After.getFromType();
-    if (CompareReferenceRelationship(Args.front()->getLocStart(),
-                                     Context.getRecordType(Shadow->getParent()),
-                                     ConvertedArgumentType, DerivedToBase,
-                                     ObjCConversion,
-                                     ObjCLifetimeConversion) >= Ref_Related) {
-      Candidate.Viable = false;
-      Candidate.FailureKind = ovl_fail_inhctor_slice;
-      return;
-    }
-  }
-
   if (EnableIfAttr *FailedAttr = CheckEnableIf(Function, Args)) {
     Candidate.Viable = false;
     Candidate.FailureKind = ovl_fail_enable_if;
@@ -10222,8 +10219,13 @@ static void NoteFunctionCandidate(Sema &S, OverloadCandidate *Cand,
     return DiagnoseOpenCLExtensionDisabled(S, Cand);
 
   case ovl_fail_inhctor_slice:
+    // It's generally not interesting to note copy/move constructors here.
+    if (cast<CXXConstructorDecl>(Fn)->isCopyOrMoveConstructor())
+      return;
     S.Diag(Fn->getLocation(),
-           diag::note_ovl_candidate_inherited_constructor_slice);
+           diag::note_ovl_candidate_inherited_constructor_slice)
+      << (Fn->getPrimaryTemplate() ? 1 : 0)
+      << Fn->getParamDecl(0)->getType()->isRValueReferenceType();
     MaybeEmitInheritedConstructorNote(S, Cand->FoundDecl);
     return;
 

clang/test/CXX/dcl.dcl/basic.namespace/namespace.udecl/p15.cpp

@@ -1,16 +1,16 @@
 // RUN: %clang_cc1 -std=c++11 -verify %s
 
-struct B1 { // expected-note 2{{candidate}}
+struct B1 {
   B1(int); // expected-note {{candidate}}
 };
 
-struct B2 { // expected-note 2{{candidate}}
+struct B2 {
   B2(int); // expected-note {{candidate}}
 };
 
 struct D1 : B1, B2 { // expected-note 2{{candidate}}
-  using B1::B1; // expected-note 3{{inherited here}}
-  using B2::B2; // expected-note 3{{inherited here}}
+  using B1::B1; // expected-note {{inherited here}}
+  using B2::B2; // expected-note {{inherited here}}
 };
 D1 d1(0); // expected-error {{ambiguous}}
 
@@ -35,7 +35,7 @@ namespace default_ctor {
     operator D&&();
   };
 
-  struct A { // expected-note 4{{candidate}}
+  struct A { // expected-note 2{{candidate}}
     A(); // expected-note {{candidate}}
 
     A(C &&); // expected-note {{candidate}}
@@ -47,7 +47,7 @@ namespace default_ctor {
     A(convert_to_D2); // expected-note {{candidate}}
   };
 
-  struct B { // expected-note 4{{candidate}}
+  struct B { // expected-note 2{{candidate}}
     B(); // expected-note {{candidate}}
 
     B(C &&); // expected-note {{candidate}}
@@ -66,9 +66,9 @@ namespace default_ctor {
     using B::operator=;
   };
   struct D : A, B {
-    using A::A; // expected-note 5{{inherited here}}
+    using A::A; // expected-note 3{{inherited here}}
     using A::operator=;
-    using B::B; // expected-note 5{{inherited here}}
+    using B::B; // expected-note 3{{inherited here}}
     using B::operator=;
 
     D(int);
@@ -93,13 +93,13 @@ namespace default_ctor {
   }
 
   struct Y;
-  struct X { // expected-note 2{{candidate}}
+  struct X {
     X();
-    X(volatile Y &); // expected-note {{constructor inherited from base class cannot be used to initialize from an argument of the derived class type}}
+    X(volatile Y &); // expected-note 3{{inherited constructor cannot be used to copy object}}
   } x;
-  struct Y : X { using X::X; } volatile y; // expected-note 2{{candidate}}
-  struct Z : Y { using Y::Y; } volatile z; // expected-note 3{{candidate}} expected-note 5{{inherited here}}
-  Z z1(x); // ok
-  Z z2(y); // ok, Z is not reference-related to type of y
+  struct Y : X { using X::X; } volatile y;
+  struct Z : Y { using Y::Y; } volatile z; // expected-note 4{{no known conversion}} expected-note 2{{would lose volatile}} expected-note 3{{requires 0}} expected-note 3{{inherited here}}
+  Z z1(x); // expected-error {{no match}}
+  Z z2(y); // expected-error {{no match}}
   Z z3(z); // expected-error {{no match}}
 }

clang/test/CXX/dcl.decl/dcl.init/dcl.init.aggr/p1.cpp

@@ -134,13 +134,13 @@ ExplicitDefaultedAggr eda2{};
 
 struct DefaultedBase {
   int n;
-  DefaultedBase() = default; // expected-note 0+ {{candidate}}
-  DefaultedBase(DefaultedBase const&) = default; // expected-note 0+ {{candidate}}
-  DefaultedBase(DefaultedBase &&) = default; // expected-note 0+ {{candidate}}
+  DefaultedBase() = default;
+  DefaultedBase(DefaultedBase const&) = default;
+  DefaultedBase(DefaultedBase &&) = default;
 };
 
 struct InheritingConstructors : DefaultedBase { // expected-note 3 {{candidate}}
-  using DefaultedBase::DefaultedBase; // expected-note 2 {{inherited here}}
+  using DefaultedBase::DefaultedBase;
 };
 InheritingConstructors ic = { 42 }; // expected-error {{no matching constructor}}
 

clang/test/CXX/drs/dr16xx.cpp

@@ -71,14 +71,14 @@ namespace dr1638 { // dr1638: yes
 
 namespace dr1645 { // dr1645: 3.9
 #if __cplusplus >= 201103L
-  struct A { // expected-note 2{{candidate}}
+  struct A {
     constexpr A(int, float = 0); // expected-note 2{{candidate}}
     explicit A(int, int = 0); // expected-note 2{{candidate}}
     A(int, int, int = 0) = delete; // expected-note {{candidate}}
   };
 
   struct B : A { // expected-note 2{{candidate}}
-    using A::A; // expected-note 7{{inherited here}}
+    using A::A; // expected-note 5{{inherited here}}
   };
 
   constexpr B a(0); // expected-error {{ambiguous}}

clang/test/CXX/drs/dr19xx.cpp

@@ -138,18 +138,21 @@ namespace dr1959 { // dr1959: 3.9
   struct c;
   struct a {
     a() = default;
-    a(const a &) = delete; // expected-note 2{{deleted}}
+    a(const a &) = delete; // expected-note {{deleted}}
     a(const b &) = delete; // not inherited
-    a(c &&) = delete;
-    template<typename T> a(T) = delete;
+    a(c &&) = delete; // expected-note {{not viable}}
+    template<typename T> a(T) = delete; // expected-note {{would take its own class type by value}}
   };
 
-  struct b : a { // expected-note {{copy constructor of 'b' is implicitly deleted because base class 'dr1959::a' has a deleted copy constructor}}
-    using a::a;
+  struct b : a { // expected-note {{cannot bind}} expected-note {{deleted because}}
+    using a::a; // expected-note 2{{inherited here}}
   };
 
   a x;
-  b y = x; // expected-error {{deleted}}
+  // FIXME: As a resolution to an open DR against P0136R0, we disallow
+  // use of inherited constructors to construct from a single argument
+  // where the base class is reference-related to the argument type.
+  b y = x; // expected-error {{no viable conversion}}
   b z = z; // expected-error {{deleted}}
 
   struct c : a {
@@ -158,7 +161,7 @@ namespace dr1959 { // dr1959: 3.9
   };
   // FIXME: As a resolution to an open DR against P0136R0, we disallow
   // use of inherited constructors to construct from a single argument
-  // where the derived class is reference-related to its type.
+  // where the base class is reference-related to the argument type.
   c q(static_cast<c&&>(q));
 #endif
 }

clang/test/CXX/special/class.inhctor/p1.cpp

@@ -3,7 +3,7 @@
 // Note: [class.inhctor] was removed by P0136R1. This tests the new behavior
 // for the wording that used to be there.
 
-struct A { // expected-note 8{{candidate is the implicit}}
+struct A { // expected-note 4{{candidate is the implicit}}
   A(...); // expected-note 4{{candidate constructor}} expected-note 4{{candidate inherited constructor}}
   A(int = 0, int = 0, int = 0, int = 0, ...); // expected-note 3{{candidate constructor}} expected-note 3{{candidate inherited constructor}}
   A(int = 0, int = 0, ...); // expected-note 3{{candidate constructor}} expected-note 3{{candidate inherited constructor}}
@@ -15,7 +15,7 @@ struct A { // expected-note 8{{candidate is the implicit}}
 };
 
 struct B : A { // expected-note 4{{candidate is the implicit}}
-  using A::A; // expected-note 19{{inherited here}}
+  using A::A; // expected-note 15{{inherited here}}
   B(void*);
 };
 

clang/test/CXX/special/class.inhctor/p3.cpp

@@ -14,21 +14,21 @@ D1 d1a(1), d1b(1, 1);
 
 D1 fd1() { return 1; }
 
-struct B2 { // expected-note 2{{candidate}}
+struct B2 {
   explicit B2(int, int = 0, int = 0);
 };
 struct D2 : B2 { // expected-note 2{{candidate constructor}}
-  using B2::B2; // expected-note 2{{inherited here}}
+  using B2::B2;
 };
 D2 d2a(1), d2b(1, 1), d2c(1, 1, 1);
 
 D2 fd2() { return 1; } // expected-error {{no viable conversion}}
 
-struct B3 { // expected-note 2{{candidate}}
+struct B3 {
   B3(void*); // expected-note {{candidate}}
 };
 struct D3 : B3 { // expected-note 2{{candidate constructor}}
-  using B3::B3; // expected-note 3{{inherited here}}
+  using B3::B3; // expected-note {{inherited here}}
 };
 D3 fd3() { return 1; } // expected-error {{no viable conversion}}
 

clang/test/CXX/special/class.inhctor/p7.cpp

@@ -3,15 +3,15 @@
 // Note: [class.inhctor] was removed by P0136R1. This tests the new behavior
 // for the wording that used to be there.
 
-struct B1 { // expected-note 2{{candidate}}
+struct B1 {
   B1(int); // expected-note {{candidate}}
 };
-struct B2 { // expected-note 2{{candidate}}
+struct B2 {
   B2(int); // expected-note {{candidate}}
 };
 struct D1 : B1, B2 { // expected-note 2{{candidate}}
-  using B1::B1; // expected-note 3{{inherited here}}
-  using B2::B2; // expected-note 3{{inherited here}}
+  using B1::B1; // expected-note {{inherited here}}
+  using B2::B2; // expected-note {{inherited here}}
 };
 struct D2 : B1, B2 {
   using B1::B1;

clang/test/SemaCXX/cxx11-inheriting-ctors.cpp

@@ -56,9 +56,9 @@ namespace InvalidConstruction {
 }
 
 namespace ExplicitConv {
-  struct B {}; // expected-note 2{{candidate}}
+  struct B {};
   struct D : B { // expected-note 3{{candidate}}
-    using B::B; // expected-note 2{{inherited}}
+    using B::B;
   };
   struct X { explicit operator B(); } x;
   struct Y { explicit operator D(); } y;
@@ -68,19 +68,40 @@ namespace ExplicitConv {
 }
 
 namespace NestedListInit {
-  struct B { B(); } b; // expected-note 5{{candidate}}
-  struct D : B { // expected-note 3{{candidate}}
-    using B::B; // expected-note 2{{inherited}}
+  struct B { B(); } b; // expected-note 3{{candidate}}
+  struct D : B { // expected-note 14{{not viable}}
+    using B::B;
   };
   // This is a bit weird. We're allowed one pair of braces for overload
   // resolution, and one more pair of braces due to [over.ics.list]/2.
   B b1 = {b};
   B b2 = {{b}};
   B b3 = {{{b}}}; // expected-error {{no match}}
-  // This is the same, but we get one call to D's version of B::B(const B&)
-  // before the two permitted calls to D::D(D&&).
-  D d1 = {b};
-  D d2 = {{b}};
-  D d3 = {{{b}}};
+  // Per a proposed defect resolution, we don't get to call
+  // D's version of B::B(const B&) here.
+  D d0 = b; // expected-error {{no viable conversion}}
+  D d1 = {b}; // expected-error {{no match}}
+  D d2 = {{b}}; // expected-error {{no match}}
+  D d3 = {{{b}}}; // expected-error {{no match}}
   D d4 = {{{{b}}}}; // expected-error {{no match}}
 }
+
+namespace PR31606 {
+  // PR31606: as part of a proposed defect resolution, do not consider
+  // inherited constructors that would be copy constructors for any class
+  // between the declaring class and the constructed class (inclusive).
+  struct Base {};
+
+  struct A : Base {
+    using Base::Base;
+    bool operator==(A const &) const; // expected-note {{no known conversion from 'PR31606::B' to 'const PR31606::A' for 1st argument}}
+  };
+
+  struct B : Base {
+    using Base::Base;
+  };
+
+  bool a = A{} == A{};
+  // Note, we do *not* allow operator=='s argument to use the inherited A::A(Base&&) constructor to construct from B{}.
+  bool b = A{} == B{}; // expected-error {{invalid operands}}
+}

clang/test/SemaTemplate/cxx1z-using-declaration.cpp

@@ -17,7 +17,7 @@ void test_Unexpanded() {
 
 // Test using non-type members from pack of base classes.
 template<typename ...T> struct A : T... { // expected-note 2{{candidate}}
-  using T::T ...; // expected-note 6{{inherited here}}
+  using T::T ...; // expected-note 2{{inherited here}}
   using T::operator() ...;
   using T::operator T* ...;
   using T::h ...;
@@ -29,7 +29,7 @@ template<typename ...T> struct A : T... { // expected-note 2{{candidate}}
 };
 
 namespace test_A {
-  struct X { // expected-note 2{{candidate}}
+  struct X {
     X();
     X(int); // expected-note {{candidate}}
     void operator()(int); // expected-note 2{{candidate}}
@@ -43,7 +43,7 @@ namespace test_A {
     operator Y *();
     void h(int, int); // expected-note {{not viable}}
   };
-  struct Z { // expected-note 2{{candidate}}
+  struct Z {
     Z();
     Z(int); // expected-note {{candidate}}
     void operator()(int); // expected-note 2{{candidate}}