[cxx2a] P0641R2: (Some) type mismatches on defaulted functions only

render the function deleted instead of rendering the program ill-formed.

This change also adds an enabled-by-default warning for the case where
an explicitly-defaulted special member function of a non-template class
is implicitly deleted by the type checking rules. (This fires either due
to this language change or due to pre-C++20 reasons for the member being
implicitly deleted). I've tested this on a large codebase and found only
bugs (where the program means something that's clearly different from
what the programmer intended), so this is enabled by default, but we
should revisit this if there are problems with this being enabled by
default.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@343285 91177308-0d34-0410-b5e6-96231b3b80d8

7 files changed, 57 insertions, 10 deletions

diff --git a/test/CXX/class.derived/class.abstract/p16.cpp b/test/CXX/class.derived/class.abstract/p16.cpp
index 80396a96d9..fe31b7321b 100644
--- a/test/CXX/class.derived/class.abstract/p16.cpp
+++ b/test/CXX/class.derived/class.abstract/p16.cpp
@@ -44,8 +44,8 @@ struct G : D {};
 // expected-error@-3 {{deleted function 'operator=' cannot override a non-deleted function}}
 // expected-note@-4 {{while declaring the implicit move assignment operator for 'G'}}
 // expected-note@-5 {{move assignment operator of 'G' is implicitly deleted because base class 'D' has an inaccessible move assignment operator}}
-struct H : D {
-  H &operator=(H&&) = default;
+struct H : D { // expected-note {{deleted because base class 'D' has an inaccessible move assignment}}
+  H &operator=(H&&) = default; // expected-warning {{implicitly deleted}}
   // expected-error@-1 {{deleted function 'operator=' cannot override a non-deleted function}}
   // expected-note@-3 {{move assignment operator of 'H' is implicitly deleted because base class 'D' has an inaccessible move assignment operator}}
   ~H();
diff --git a/test/CXX/dcl.decl/dcl.fct.def/dcl.fct.def.default/p1.cpp b/test/CXX/dcl.decl/dcl.fct.def/dcl.fct.def.default/p1.cpp
index 51993307cf..3f2bc569ed 100644
--- a/test/CXX/dcl.decl/dcl.fct.def/dcl.fct.def.default/p1.cpp
+++ b/test/CXX/dcl.decl/dcl.fct.def/dcl.fct.def.default/p1.cpp
@@ -1,15 +1,30 @@
 // RUN: %clang_cc1 -verify %s -std=c++11
+// RUN: %clang_cc1 -verify %s -std=c++17
+// RUN: %clang_cc1 -verify %s -std=c++2a
 
 // A function that is explicitly defaulted shall
 struct A {
   // -- be a special member function,
   A(int) = default; // expected-error {{only special member functions may be defaulted}}
+  A(A) = default; // expected-error {{must pass its first argument by reference}}
 
   // -- have the same declared function type as if it had been implicitly
   //    declared
   void operator=(const A &) = default; // expected-error {{must return 'A &'}}
-  A(...) = default; // expected-error {{cannot be variadic}}
-  A(const A &, ...) = default; // expected-error {{cannot be variadic}}
+  A(...) = default;
+  A(const A &, ...) = default;
+  A &operator=(const A&) const = default;
+  A &operator=(A) const = default; // expected-error {{must be an lvalue refe}}
+#if __cplusplus <= 201703L
+  // expected-error@-5 {{cannot be variadic}}
+  // expected-error@-5 {{cannot be variadic}}
+  // expected-error@-5 {{may not have 'const'}}
+  // expected-error@-5 {{may not have 'const'}}
+#else
+  // expected-warning@-10 {{implicitly deleted}} expected-note@-10 {{declared type does not match the type of an implicit default constructor}}
+  // expected-warning@-10 {{implicitly deleted}} expected-note@-10 {{declared type does not match the type of an implicit copy constructor}}
+  // expected-warning@-10 {{implicitly deleted}} expected-note@-10 {{declared type does not match the type of an implicit copy assignment}}
+#endif
 
   //    (except for possibly differing ref-qualifiers
   A &operator=(A &&) & = default;
@@ -23,3 +38,35 @@ struct A {
   A(double = 0.0) = default; // expected-error {{cannot have default arguments}}
   A(const A & = 0) = default; // expected-error {{cannot have default arguments}}
 };
+
+struct A2 {
+  A2(...);
+  A2(const A2 &, ...);
+  A2 &operator=(const A2&) const;
+};
+A2::A2(...) = default; // expected-error {{cannot be variadic}}
+A2::A2(const A2&, ...) = default; // expected-error {{cannot be variadic}}
+A2 &A2::operator=(const A2&) const = default; // expected-error {{may not have 'const'}}
+
+struct B {
+  B(B&);
+  B &operator=(B&);
+};
+struct C : B {
+  C(const C&) = default;
+  C &operator=(const C&) = default;
+#if __cplusplus <= 201703L
+  // expected-error@-3 {{is const, but a member or base requires it to be non-const}}
+  // expected-error@-3 {{is const, but a member or base requires it to be non-const}}
+#else
+  // expected-warning@-6 {{implicitly deleted}} expected-note@-6 {{type does not match}}
+  // expected-warning@-6 {{implicitly deleted}} expected-note@-6 {{type does not match}}
+#endif
+};
+
+struct D : B { // expected-note 2{{base class}}
+  D(const D&);
+  D &operator=(const D&);
+};
+D::D(const D&) = default; // expected-error {{would delete}} expected-error {{is const, but}}
+D &D::operator=(const D&) = default; // expected-error {{would delete}} expected-error {{is const, but}}
diff --git a/test/CXX/drs/dr6xx.cpp b/test/CXX/drs/dr6xx.cpp
index c3c867b7a5..0f072268ab 100644
--- a/test/CXX/drs/dr6xx.cpp
+++ b/test/CXX/drs/dr6xx.cpp
@@ -757,8 +757,8 @@ namespace dr666 { // dr666: yes
 #if __cplusplus >= 201103L
 namespace dr667 { // dr667: yes
   struct A {
-    A() = default;
-    int &r;
+    A() = default; // expected-warning {{explicitly defaulted default constructor is implicitly deleted}}
+    int &r; // expected-note {{because field 'r' of reference type 'int &' would not be initialized}}
   };
   static_assert(!__is_trivially_constructible(A), "");
 
diff --git a/test/CXX/special/class.copy/p12-0x.cpp b/test/CXX/special/class.copy/p12-0x.cpp
index 1b23b5a4b1..a0ef49d9b6 100644
--- a/test/CXX/special/class.copy/p12-0x.cpp
+++ b/test/CXX/special/class.copy/p12-0x.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++11 -verify %s
+// RUN: %clang_cc1 -std=c++11 -verify %s -Wno-defaulted-function-deleted
 
 // expected-no-diagnostics
 
diff --git a/test/CXX/special/class.copy/p23-cxx11.cpp b/test/CXX/special/class.copy/p23-cxx11.cpp
index ac21cc61a2..0b9652b50f 100644
--- a/test/CXX/special/class.copy/p23-cxx11.cpp
+++ b/test/CXX/special/class.copy/p23-cxx11.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -verify %s -std=c++11
+// RUN: %clang_cc1 -verify %s -std=c++11 -Wno-defaulted-function-deleted
 
 struct Trivial {};
 
diff --git a/test/CXX/special/class.ctor/p5-0x.cpp b/test/CXX/special/class.ctor/p5-0x.cpp
index 061a3d1f07..5fa61008e8 100644
--- a/test/CXX/special/class.ctor/p5-0x.cpp
+++ b/test/CXX/special/class.ctor/p5-0x.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++11
+// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++11 -Wno-defaulted-function-deleted
 
 struct DefaultedDefCtor1 {};
 struct DefaultedDefCtor2 { DefaultedDefCtor2() = default; };
diff --git a/test/CXX/special/class.dtor/p5-0x.cpp b/test/CXX/special/class.dtor/p5-0x.cpp
index 595784f0d5..f69baca53b 100644
--- a/test/CXX/special/class.dtor/p5-0x.cpp
+++ b/test/CXX/special/class.dtor/p5-0x.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -verify -std=c++11 %s
+// RUN: %clang_cc1 -verify -std=c++11 %s -Wno-defaulted-function-deleted
 
 struct NonTrivDtor {
   ~NonTrivDtor();