Add tests for move.

Note that if there is an invalid move constructor,
overload resolution will try to pick a copy constructor instead.

Author: cor3ntin

clang/test/SemaCXX/cxx2b-deducing-this.cpp

@@ -608,11 +608,21 @@ S2& S2::operator=(this int&& self, const S2&) = default;
 S2& S2::operator=(this int&& self, S2&&) = default;
 // expected-error@-1 {{the type of the explicit object parameter of an explicitly-defaulted move assignment operator should match the type of the class 'S2'}}
 
+struct Move {
+    Move& operator=(this int&, Move&&) = default;
+    // expected-warning@-1 {{explicitly defaulted move assignment operator is implicitly deleted}}
+    // expected-note@-2 {{function is implicitly deleted because its declared type does not match the type of an implicit move assignment operator}}
+    // expected-note@-3 {{copy assignment operator is implicitly deleted because 'Move' has a user-declared move assignment operator}}
+};
+
 void test() {
     S s;
     s = s; // expected-error {{object of type 'S' cannot be assigned because its copy assignment operator is implicitly deleted}}
     S2 s2;
     s2 = s2;
+
+    Move m;
+    m = Move{}; // expected-error {{object of type 'Move' cannot be assigned because its copy assignment operator is implicitly deleted}}
 }
 
 }