[Bug c++/58119] New: Invalid ambiguous default type conversion with only a single invalid conversion listed.

[Bug c++/58119] New: Invalid ambiguous default type conversion with only a single invalid conversion listed.

[tilps at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58119

            Bug ID: 58119
           Summary: Invalid ambiguous default type conversion with only a
                    single invalid conversion listed.
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tilps at hotmail dot com

'Minimal' test case:
template <class type>
class Silly {
 public:
  Silly(type *value) {
    data_ = value;
  }
  operator type*() const {
    return data_;
  }
  template <class other>
  operator Silly<other>() const {
    return Silly<other>(data_);
  }
 private:
  type *data_;
};

int main() {
  Silly<int> a(nullptr);
  delete a;
}

Fails giving:
test.cc:20:10: error: ambiguous default type conversion from 'Silly<int>'
   delete a;
          ^
test.cc:20:10: error:   candidate conversions include 'template<class other>
Silly<type>::operator Silly<other>() const [with other = other; type = int]'
test.cc:20:10: error: type 'class Silly<int>' argument given to 'delete',
expected pointer

I believe that this code should be considered valid, the only valid type
conversion is via the operator type *() which then converts to void* for the
delete operator.  I don't see any way that Silly<anything> could be considered
convertible, except via operator type *() - and as far as I was aware, only a
single implicit cast operator is allowed to be considered in a type conversion
chain.
Interestingly, the valid type conversion is not mentioned as a candidate, and
the candidate mentioned does not specify which template parameter type it would
use for the 'other' template parameter.

Ultimately this is a bit of a strange example - I was trying to resurrect some
legacy code with a particularly dumb (but heavily used) 'smart pointer' type. 
But this code did work, at least as recently as 4.6 - and probably back before
3.2.

[Bug c++/58119] [4.7/4.8/4.9 Regression] Invalid ambiguous default type conversion with only a single invalid conversion listed.

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58119

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-08-10
                 CC|                            |jason at gcc dot gnu.org
            Summary|Invalid ambiguous default   |[4.7/4.8/4.9 Regression]
                   |type conversion with only a |Invalid ambiguous default
                   |single invalid conversion   |type conversion with only a
                   |listed.                     |single invalid conversion
                   |                            |listed.
     Ever confirmed|0                           |1

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> ---
I'm marking this as Regression because 4.6.x accepted it (likewise current
clang and icc)

[Bug c++/58119] [4.7/4.8/4.9 Regression] Invalid ambiguous default type conversion with only a single invalid conversion listed.

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58119

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org
   Target Milestone|---                         |4.7.4

[Bug c++/58119] [4.7/4.8/4.9 Regression] Invalid ambiguous default type conversion with only a single invalid conversion listed.

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58119

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org

[Bug c++/58119] [4.7/4.8/4.9 Regression] Invalid ambiguous default type conversion with only a single invalid conversion listed.

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58119

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for trunk, 4.7, 4.8 in r201880, r201881, r201882.