[LLVMbugs] [Bug 20783] New: Deduction for reference conversion template discards cv-qualifiers

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20783

            Bug ID: 20783
           Summary: Deduction for reference conversion template discards
                    cv-qualifiers
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++11
          Assignee: unassignedclangbugs at nondot.org
          Reporter: hstong at ca.ibm.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

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

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