[Bug c++/42356] New: confused compiler

[Bug c++/42356] New: confused compiler

[igodard at pacbell dot net]

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This code:
template<typename T>
class   freeList {
public:
    T*      newNode() { return 0; }
    template<typename U>
    T*      newNode(U u) { return newNode()->init(u); }
    template<typename U, typename V>
    T*      newNode(U u, V v) { return newNode()->init(u, v); }
    };

class   bar {};
class   baz {};
class   foo : public freeList<bar>, public freeList<baz> { };

int main() {
    foo     f;
    bar*    b = f.newNode<bar>();
    }


gets you:
s3:~/ootbc/memspec$ g++ foo.cc
foo.cc: In function ‘int main()’:
foo.cc:17: error: request for member ‘newNode’ is ambiguous
foo.cc:8: error: candidates are: template<class U, class V> T*
freeList::newNode(U, V) [with U = U, V = V, T = baz]
foo.cc:6: error: candidates are: template<class U> T* freeList::newNode(U)
[with U = U, T = baz]
foo.cc:4: error: candidates are: T* freeList<T>::newNode() [with T = baz]
foo.cc:8: error:                 template<class U, class V> T*
freeList::newNode(U, V) [with U = U, V = V, T = bar]
foo.cc:6: error:                 template<class U> T* freeList::newNode(U)
[with U = U, T = bar]
foo.cc:4: error:                 T* freeList<T>::newNode() [with T = bar]
foo.cc:17: error: expected primary-expression before ‘>’ token
foo.cc:17: error: expected primary-expression before ‘)’ token


-- 
           Summary: confused compiler
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: igodard at pacbell dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42356

[Bug c++/42356] confused compiler

[paolo dot carlini at oracle dot com]

------- Comment #1 from paolo dot carlini at oracle dot com  2009-12-12 09:47 -------
The basic error, at line 17, is definitely correct, and, for example, ICC
errors out exactly in the same way. I suppose you would like to see a nicer, in
some sense, list of candidates? (by the way, mailine is slightly better anyway,
because doesn't make the mistake of printing the words "candidates are:"
multiple times)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42356

[Bug c++/42356] confused compiler

[igodard at pacbell dot net]

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------- Comment #2 from igodard at pacbell dot net  2009-12-14 04:51 -------
Well, I see several issues with the diagnostics. 

1) The call is not ambiguous, because if it were (only) ambiguous then removing
the base "baz" would disambiguate. Instead the case without "baz" gets you:
   s3:~/ootbc/memspec$ g++ foo.cc
   foo.cc: In function ‘int main()’:
   foo.cc:27: error: no matching function for call to ‘foo::newNode()’
That is, a call cannot be both ambiguous and have no matching function.

2) The reported list of overloads include those which have the wrong number of
arguments.

3) The diagnostic contains "freeList::newNode(U, V) [with U = U, V = V, T =
bar]" as the call citation, which makes it look like the local U matches a
(non-existent in this case) global U and local V matches a global V, the way
that local T matches global bar. Perhaps it could say something like
"freeList::newNode(U, V) [with U = ?, V = ?, T = bar]"


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42356

[Bug c++/42356] confused compiler

[paolo dot carlini at oracle dot com]

------- Comment #3 from paolo dot carlini at oracle dot com  2009-12-14 08:44 -------
I do not have the time to get into the language details, but I think you should
investigate the conformance of the code a bit more: recent SunStudio and Comeau
also agree with ICC and GCC on this.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42356

[Bug c++/42356] confused compiler

[paolo dot carlini at oracle dot com]

------- Comment #4 from paolo dot carlini at oracle dot com  2009-12-14 09:27 -------
Likewise VC++ v8


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42356

[Bug c++/42356] confused compiler

[igodard at pacbell dot net]

------- Comment #5 from igodard at pacbell dot net  2009-12-14 14:58 -------
There's no question that there was an error here. The report is on the
diagnostic. I'm sorry if I hadn't made that clear.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42356

[Bug c++/42356] confused compiler

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42356

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-10-22
                 CC|                            |manu at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #7 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2011-10-22 12:27:11 UTC ---
Clang prints:

/tmp/webcompile/_26276_0.cc:17:19: error: no matching member function for call
to 'newNode'
    bar*    b = f.newNode<bar>();
                ~~^~~~~~~~~~~~
/tmp/webcompile/_26276_0.cc:6:13: note: candidate function template not viable:
requires 1 argument, but 0 were provided
    T*      newNode(U u) { return newNode()->init(u); }
            ^
/tmp/webcompile/_26276_0.cc:6:13: note: candidate function template not viable:
requires 1 argument, but 0 were provided
/tmp/webcompile/_26276_0.cc:8:13: note: candidate function template not viable:
requires 2 arguments, but 0 were provided
    T*      newNode(U u, V v) { return newNode()->init(u, v); }
            ^
/tmp/webcompile/_26276_0.cc:8:13: note: candidate function template not viable:
requires 2 arguments, but 0 were provided

which is nicer except for the duplicated messages.

The first thing that should go away is the "expected primary-expression" stuff.

[Bug c++/42356] confused compiler

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42356

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

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

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-28 21:21:40 UTC ---
For the record, ICC also thinks it's ambiguous.