[Bug c++/19741] New: less than optimal error message (actually, just appears wrong, use of <unknown_type>?)

[Bug c++/19741] New: less than optimal error message (actually, just appears wrong, use of <unknown_type>?)

[eda-qa at disemia dot com]

(Such an error also appears to exist in 5458)

In the attached example the following error appears:
tpladdr.cc: In function `int main()':
tpladdr.cc:21: error: no matching function for call to `Op<int>::Exec(int,
<unknown type>)'
tpladdr.cc:14: error: candidates are: static bool Op<T>::Exec(T, bool (*)(T))
[with T = int]

In this case the error does not help (actually it misleads) as to what the
problem is.  The reference to <unknown_type> seems to indicate that it doesn't
know the type of that paremeter, when in indeed it actually does, but the
function type has the wrong signature...

Simply correcting the function signature to:
bool Func( T param )

Allows the program to work as it should.

Thus the error message is simply very confusing.

-- 
           Summary: less than optimal error message (actually, just appears
                    wrong, use of <unknown_type>?)
           Product: gcc
           Version: 3.3.1
            Status: UNCONFIRMED
          Severity: minor
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: eda-qa at disemia dot com
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19741

[Bug c++/19741] less than optimal error message (actually, just appears wrong, use of <unknown_type>?)

[eda-qa at disemia dot com]

------- Additional Comments From eda-qa at disemia dot com  2005-02-01 14:06 -------
Created an attachment (id=8121)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=8121&action=view)
test case


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19741

[Bug c++/19741] suboptimal error message for template functions (as opposed to non-templates)

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2005-02-01 14:27 -------
This is in fact true. There is a mismatch between error messages for 
template function arguments and non-templates: 
-------------------- 
                    void foo1(); 
template <typename> void foo2(); 
 
template <typename> bool bar(void (*) () ); 
 
bool b1 = bar<int> (1, &foo1); 
bool b2 = bar<int> (1, &foo2<int>); 
-------------------- 
g/x> /home/bangerth/bin/gcc-4.0-pre/bin/c++ -c x.cc 
x.cc:6: error: no matching function for call to ?bar(int, void (*)())? 
x.cc:7: error: no matching function for call to ?bar(int, <unknown type>)? 
 
Since the complete template arguments to foo2 are given, the type should 
in fact be completely known. 
 
W. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2005-02-01 14:27:13
               date|                            |
            Summary|less than optimal error     |suboptimal error message for
                   |message (actually, just     |template functions (as
                   |appears wrong, use of       |opposed to non-templates)
                   |<unknown_type>?)            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19741

[Bug c++/19741] suboptimal error message for template functions (as opposed to non-templates)

[gdr at integrable-solutions dot net]

------- Additional Comments From gdr at integrable-solutions dot net  2005-02-01 16:04 -------
Subject: Re:  suboptimal error message for template functions (as opposed to non-templates)

"bangerth at dealii dot org" <gcc-bugzilla@gcc.gnu.org> writes:

| This is in fact true. There is a mismatch between error messages for 
| template function arguments and non-templates: 
| -------------------- 
|                     void foo1(); 
| template <typename> void foo2(); 
|  
| template <typename> bool bar(void (*) () ); 
|  
| bool b1 = bar<int> (1, &foo1); 
| bool b2 = bar<int> (1, &foo2<int>); 
| -------------------- 
| g/x> /home/bangerth/bin/gcc-4.0-pre/bin/c++ -c x.cc 
| x.cc:6: error: no matching function for call to ?bar(int, void (*)())? 
| x.cc:7: error: no matching function for call to ?bar(int, <unknown type>)? 
|  
| Since the complete template arguments to foo2 are given, the type should 
| in fact be completely known. 

Agreed.

(More generally, I think the C++ front-end should have a type for
overload set and -- by means of implication for templates too -- to
better capture user mistakes.)

-- Gaby


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19741

[Bug c++/19741] suboptimal error message for template functions (as opposed to non-templates)

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2005-02-01 17:30 -------
Except that, of course, in the present case the overload set contains 
only a single function (foo2 isn't overloaded, and we have specified 
all template arguments). Which should make it even easier to handle 
this particular case. 
 
W. 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19741

[Bug c++/19741] suboptimal error message for template functions (as opposed to non-templates)

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19741

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-01-20 02:56:03 UTC ---
We get on the trunk:
t.cc: In function ‘int main()’:
t.cc:21:33: error: no matching function for call to ‘Op<int>::Exec(int,
<unresolved overloaded function type>)’
t.cc:21:33: note: candidate is:
t.cc:13:14: note: static bool Op<T>::Exec(T, Op<T>::op_func) [with T = int;
Op<T>::op_func = bool (*)(int)]
t.cc:13:14: note:   no known conversion for argument 2 from ‘<unresolved
overloaded function type>’ to ‘Op<int>::op_func {aka bool (*)(int)}’
t.cc: In instantiation of ‘static bool Op<T>::Exec(T, Op<T>::op_func) [with T =
int; Op<T>::op_func = bool (*)(int)]’:
t.cc:21:11:   required from here
t.cc:15:25: warning: cast to pointer from integer of different size
[-Wint-to-pointer-cast]

[Bug c++/19741] suboptimal error message for template functions (as opposed to non-templates)

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2005-10-04 02:32 -------
The error message was changed by:
Fixed by:
        * error.c (dump_type) <UNKNOWN_TYPE>: Print reworded message.
        * g++.dg/overload/unknown1.C: New.

But reading comment 4, that will not fix the issue fully.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19741