Deduction for reference conversion template discards cv-qualifiers


Bugzilla Link	PR20783
Status	NEW
Importance	P normal
Reported by	hstong@ca.ibm.com
Reported on	2014-08-27 21:53:51 -0700
Last modified on	2017-04-29 21:22:07 -0700
Version	trunk
Hardware	All All
CC	dgregor@apple.com, eniebler@boost.org, llvm-bugs@lists.llvm.org
Fixed by commit(s)
Attachments
Blocks
Blocked by
See also

Template argument deduction for reference conversions do not deduce the correct
type with respect to cv-qualifiers of the deduced A.

See N3290 subclause 14.8.2.3 [temp.deduct.conv]; the P/A pair used for type
deduction in the case below would be T/const int.
Deduction should succeed with T = const int.

As the error message shows, the deduction produced "int" instead of "const int".

### SOURCE:
$ cat deduceTemplateConv.cc
struct A {
  template <typename T> operator T&() { static_assert(sizeof(T) == 0, ""); }
};
template <> A::operator const int &(void);

const int &x = A();

### COMPILER INVOCATION AND OUTPUT:
$ clang -x c++ -std=c++11 deduceTemplateConv.cc
deduceTemplateConv.cc:2:41: error: static_assert failed ""
  template <typename T> operator T&() { static_assert(sizeof(T) == 0, ""); }
                                        ^             ~~~~~~~~~~~~~~
deduceTemplateConv.cc:6:16: note: in instantiation of function template
specialization 'A::operator int &<int>' requested here
const int &x = A();
               ^
1 error generated.

### EXPECTED OUTPUT:
Successful compile.

### COMPILER VERSION INFO:
$ clang++ -v
clang version 3.6.0 (trunk 215824)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Candidate multilib: .;@m64
Selected multilib: .;@m64

Quuxplusone / LLVMBugzillaTest

Deduction for reference conversion template discards cv-qualifiers #20782