[clang] Add test for CWG2007

[Endill]

Summary

P1787: CWG2007 is resolved by skipping unqualified lookup for operators that must be member functions.
Wording: For the operators =, [], or ->, the set of non-member candidates is empty; otherwise, it includes the result of the unqualified lookup for operator@... ([over.match.oper]/3)

[shafik]

clang/test/CXX/drs/dr20xx.cpp

20

It looks like gcc and MSVC also instantiate A<void> for this case: https://godbolt.org/z/8W8eYoa38

I have to think about it some more but if we believe clang is wrong here, you should file a bug report.

[shafik]

clang/test/CXX/drs/dr20xx.cpp

20

I think unary & is triggering the instantiation.

[Endill]

clang/test/CXX/drs/dr20xx.cpp

20

Does it mean that we should craft a better example?

[shafik]

clang/test/CXX/drs/dr20xx.cpp

20

Yes, we need a better example, something like this will work, maybe something like:

cpp
B<A<void> > arr[2];
auto x = arr->foo;

[Endill]

Replace unary & with __builtin_addressof(). It prevents unnecessary template instantiation (presumably to find overloaded unary &), and make Clang compliant since 3.4

[shafik]

In D147839#4257394, @Endill wrote:

Replace unary & with __builtin_addressof(). It prevents unnecessary template instantiation (presumably to find overloaded unary &), and make Clang compliant since 3.4

Nice approach!

[shafik]

LGTM, thank you again for all the effort in documenting these and adding tests, it is much appreciated.

[Endill]

In D147839#4258681, @shafik wrote:

In D147839#4257394, @Endill wrote:

Replace unary & with __builtin_addressof(). It prevents unnecessary template instantiation (presumably to find overloaded unary &), and make Clang compliant since 3.4

Nice approach!

Credits go to Aaron, actually. We discussed this DR during his office hours yesterday.

In D147839#4258682, @shafik wrote:

LGTM, thank you again for all the effort in documenting these and adding tests, it is much appreciated.

Thank you for giving them thorough review.

[Endill]

rebase

clang/test/CXX/drs/dr20xx.cpp

 // RUN: %clang_cc1 -std=c++98 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors \
 // RUN:            -Wno-variadic-macros -Wno-c11-extensions
 // RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
 // RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
 // RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
-// RUN: %clang_cc1 -std=c++2a -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++2b -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
 
 #if __cplusplus < 201103L
 #define static_assert(...) _Static_assert(__VA_ARGS__)
 #endif
 
+namespace dr2007 { // dr2007: 3.4
+template<typename T> struct A { typename T::error e; };
+template<typename T> struct B { };
+B<A<void> > b1;
+B<A<void> > b2 = b1;
+int a = b2[0]; // expected-error {{does not provide a subscript operator}}
+int b = __builtin_addressof(b2)->foo; // expected-error {{no member}}
+}
+
 namespace dr2026 { // dr2026: 11
   template<int> struct X {};
 
   const int a = a + 1; // expected-warning {{uninitialized}} expected-note {{here}} expected-note 0-1{{outside its lifetime}}
   X<a> xa; // expected-error {{constant expression}} expected-note {{initializer of 'a'}}
 
 #if __cplusplus >= 201103L
   constexpr int b = b; // expected-error {{constant expression}} expected-note {{outside its lifetime}}

clang/www/cxx_dr_status.html

<tr id="2006">
     <td>CD4</td>
     <td>Cv-qualified <TT>void</TT> types</td>
     <td class="none" align="center">Unknown</td>
   </tr>
   <tr id="2007">
     <td><a href="https://wg21.link/cwg2007">2007</a></td>
     <td>CD6</td>
     <td>Argument-dependent lookup for <TT>operator=</TT></td>
-    <td class="none" align="center">Unknown</td>
+    <td class="full" align="center">Clang 3.4</td>
   </tr>
   <tr id="2008">
     <td><a href="https://wg21.link/cwg2008">2008</a></td>
     <td>CD4</td>
     <td>Default <I>template-argument</I>s underspecified</td>
     <td class="none" align="center">Unknown</td>
   </tr>
   <tr id="2009">