[Bug c++/51817] New: [C++11] argument deduction fails when A-type parameter-type-list has additional parameters

[Bug c++/51817] New: [C++11] argument deduction fails when A-type parameter-type-list has additional parameters

[hstong at ca dot ibm.com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51817

             Bug #: 51817
           Summary: [C++11] argument deduction fails when A-type
                    parameter-type-list has additional parameters
    Classification: Unclassified
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hstong@ca.ibm.com
              Host: powerpc64-unknown-linux-gnu
            Target: powerpc64-unknown-linux-gnu


The behaviour of the following test case was clarified in paper N2242 for
variadic templates.

In the 2011 FDIS subclause 14.8.2.5 [temp.deduct.type] paragraph 10,
deduction from a function type considers P/A pairs from the
parameter-type-list only where the "P" function type has a parameter.

Deduction is not specified to fail if there are additional parameters in the
corresponding "A" function type.

I use the --std=c++0x option; however, I do not believe that the C++03 wording
prohibits the C++2011 behaviour.

The second call to foo in main should be the same as the first (working) call.

If compiled and linked with -DVERBOSE, the resulting program should print:
Converting from A<void (int, char)> to A<void (int)>.
foo(A<void (int)> called.
Converting from A<void (int, char)> to A<void (int)>.
foo(A<void (int)> called.


### Self-contained source:
$ cat parmlistlen.cpp
template <typename U>
struct A {
   template <typename V> operator A<V>();
};

template <typename T> void foo(A<void (T)>);
void foo();

int main() {
   A<void (int, char)> a;
   foo<int>(a);
   foo(a);  // seems to fail in argument deduction
}

#ifdef VERBOSE
extern "C" int printf(const char *, ...);

template <typename T> struct tyStr { static const char str[]; };
template <> const char tyStr<void (int, char)>::str[] = "void (int, char)";
template <> const char tyStr<void (int)>::str[] = "void (int)";

template <typename T>
void foo(A<void (T)>) {
   printf("foo(A<%s> called.\n", tyStr<void (T)>::str);
}

template <typename U>
template <typename V>
A<U>::operator A<V>() {
   printf("Converting from A<%s> to A<%s>.\n", tyStr<U>::str, tyStr<V>::str);
   return A<V>(); 
}
#endif


### Compiler Invocation:
$ g++-4.6.0 --std='c++0x' parmlistlen.cpp
parmlistlen.cpp: In function 'int main()':
parmlistlen.cpp:12:9: error: no matching function for call to 'foo(A<void(int,
char)>&)'
parmlistlen.cpp:12:9: note: candidates are:
parmlistlen.cpp:6:28: note: template<class T> void foo(A<void(T)>)
parmlistlen.cpp:7:6: note: void foo()
parmlistlen.cpp:7:6: note:   candidate expects 0 arguments, 1 provided


### g++ -v output:
$ g++-4.6.0 -v             
Using built-in specs.
COLLECT_GCC=g++-4.6.0
COLLECT_LTO_WRAPPER=/data/gcc/libexec/gcc/powerpc64-unknown-linux-gnu/4.6.0/lto-wrapper
Target: powerpc64-unknown-linux-gnu
Configured with: ./configure --prefix=/data/gcc --program-suffix=-4.6.0
--disable-libssp --disable-libgcj --enable-version-specific-runtime-libs
--with-cpu=default32 --enable-secureplt --with-long-double-128 --enable-shared
--enable-__cxa_atexit --enable-threads=posix --enable-languages=c,c++,fortran
--with-gmp=/usr/local
Thread model: posix
gcc version 4.6.0 (GCC)

[Bug c++/51817] [C++11] argument deduction fails when A-type parameter-type-list has additional parameters

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51817

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> ---
I think this is the expected behavior. Note that current clang and EDG behave
exactly the same, reject the testcase with an error at line 12.

Maybe Jason can help me completing the triage of this?