[LLVMbugs] [Bug 11942] New: Hidden type name causes confusion

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=11942

             Bug #: 11942
           Summary: Hidden type name causes confusion
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: chris at bubblescope.net
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified


The following comes from reducing an example which used std::map iterators. The
code below produces the following error message:

-----------------

t.cc:24:7: error: invalid operands to binary expression
('MyBase<MyMap>::base_iterator' (aka 'P<typename MyMap::type>') and 'P<int>')
  *it == p;  
  ~~~ ^  ~
t.cc:6:6: note: candidate template ignored: deduced conflicting types for
parameter 'T' ('const int' vs. 'int')
void operator==(const P<T>&, const P<T>&)

-----------------

Notice the 'aka' doesn't actually tell us the type, so we still don't really
know what the problem is. In this case, the 'note' is quite helpful, but in
other cases is less useful. Should the 'aka' aim to give the "real type" of the
expression?

Code example:

template<typename T>
struct P
{ };

template<typename T>
void operator==(const P<T>&, const P<T>&)
{ };

template<typename M>
struct MyBase
{ typedef P<typename M::type> base_iterator; };

struct MyMap
{
    typedef const int type;
    typedef MyBase<MyMap>::base_iterator* iterator;
};

int main(void)
{
  MyMap::iterator it;
  P<int> p;
  *it == p;  
}

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