[llvm-bugs] [Bug 31450] New: poor diagnostics for ambiguous template function instantation

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=31450

            Bug ID: 31450
           Summary: poor diagnostics for ambiguous template function
                    instantation
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: compnerd at compnerd.org
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Consider the following code:

namespace n {
int f(void *);

template <int> int g(void *);

extern template int g<0>(void *);
}

using namespace n;

template <int> int g(void *p) { return 0; }

template int g<0>(void *);

The template function here is ambiguous because we have n::g and ::g.

We diagnose this as:

$ clang -fsyntax-only -std=c++11 /tmp/reduced.cc
/tmp/reduced.cc:13:14: error: partial ordering for explicit instantiation of
'g' is ambiguous
template int g<0>(void *);
             ^
/tmp/reduced.cc:11:20: note: explicit instantiation candidate function template
here [with $0 = 0]
template <int> int g(void *p) { return 0; }
                   ^
/tmp/reduced.cc:4:20: note: explicit instantiation candidate function template
here [with $0 = 0]
template <int> int g(void *);
                   ^
While gcc diagnoses this as:

$ c++ -fsyntax-only -std=c++11 /tmp/reduced.cc
/tmp/reduced.cc:13:14: error: ambiguous template specialization 'g<0>' for 'int
g(void*)'
 template int g<0>(void *);
              ^
/tmp/reduced.cc:11:20: note: candidates are: template<int <anonymous> > int
g(void*)
 template <int> int g(void *p) { return 0; }
                    ^
/tmp/reduced.cc:4:20: note:                 template<int <anonymous> > int
n::g(void*)
 template <int> int g(void *);

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