[LLVMdev] Clang bug?

Richard Smith richard at metafoo.co.uk
Fri Sep 28 14:54:30 PDT 2012


Reduced testcase:

template<typename T> struct A { typedef decltype(T() + 0) type; };
template<typename T> struct B {
  struct C { typedef typename A<C*>::type type; };
  typedef typename A<C*>::type type;
};
B<int> b;

... produces ...

<stdin>:3:38: error: no type named 'type' in 'A<B<int>::C *>'
  struct C { typedef typename A<C*>::type type; };
                     ~~~~~~~~~~~~~~~~^~~~
<stdin>:1:54: note: in instantiation of member class 'B<int>::C' requested
here
template<typename T> struct A { typedef decltype(T() + 0) type; };
                                                     ^
<stdin>:4:20: note: in instantiation of template class 'A<B<int>::C *>'
requested here
  typedef typename A<C*>::type type;
                   ^
<stdin>:6:8: note: in instantiation of template class 'B<int>' requested
here
B<int> b;
       ^

I think it would be worth filing this as a diagnostic QoR issue. We should
be able to say something like

<stdin>:3:38: error: member 'type' of 'A<B<int>::C *>' required recursively
within the instantiation of 'A<B<int>::C *>', but it has not been
instantiated yet

On Fri, Sep 28, 2012 at 7:51 AM, Howard Hinnant <hhinnant at apple.com> wrote:

> That is one evil bug!
>
> I just tested it against tip-of-trunk clang and it appears to be fixed
> there (just fyi for everyone).
>
> Howard
>
> On Sep 27, 2012, at 7:17 PM, Adam Peterson <alpha.eta.pi at gmail.com> wrote:
>
> > Is this a relevant location to provide information about what I
> > believe is a compiler bug in clang?  If not, please forgive me for
> > posting it here.  (Perhaps you can redirect me to some place more
> > appropriate.)  If so, here are the details:
> >
> > I have a short 15-line C++ program using only one standard header that
> > clang fails to compile properly under C++11 with the new standard
> > library (although the code itself doesn't use any C++11-specific
> > syntax), but G++ (4.6-Ubuntu and 4.2-Darwin) compiles it fine:
> >
> >    #include <map>
> >    using std::map;
> >
> >    template<typename K>
> >    struct Templ8 {
> >        struct Member {
> >            typename map<K,Member*>::iterator it;
> >        };
> >        typedef typename map<K,Member*>::iterator iterator_type;
> >    };
> >
> >    int main() {
> >        Templ8<int> test;
> >    }
> >
> >
> >
> > This is the command-line:
> >    clang++ -stdlib=libc++ -std=c++11 main_bug.cpp
> > If either of the flags are removed (to compile in C++03 mode, or to
> > use the non-clang standard library), the code compiles.  If the
> > typedef is removed or commented out, clang++ compiles the code fine.
> > If the typedef is moved inside the "Member" inner class, the code
> > compiles fine (even if a second typedef pulls the symbol back into the
> > main template scope).
> >
> > My clang version information:
> >    Apple clang version 4.1 (tags/Apple/clang-421.11.65) (based on LLVM
> 3.1svn)
> >    Target: x86_64-apple-darwin12.2.0
> >    Thread model: posix
> >
> > The error output:
> >
> > main_bug.cpp:7:34: error: no type named 'iterator' in
> > 'std::__1::map<int, Templ8<int>::Member *, std::__1::less<int>,
> > std::__1::allocator<std::__1::pair<const int, Templ8<int>::Member
> > *>>>'
> >        typename map<K,Member*>::iterator it;
> >        ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
> > /usr/bin/../lib/c++/v1/type_traits:1184:57: note: in instantiation of
> > member class 'Templ8<int>::Member' requested here
> > decltype((_VSTD::declval<_Tp>() = _VSTD::declval<_Arg>(), true_type()))
> >                                                        ^
> > /usr/bin/../lib/c++/v1/type_traits:1186:1: note: while substituting
> > deduced template arguments into function template
> > '__is_assignable_test' [with _Tp = Templ8<int>::Member *&, _Arg = <no
> > value>]
> > __is_assignable_test(_Tp&&, _Arg&&);
> > ^
> > /usr/bin/../lib/c++/v1/type_traits:1214:14: note: in instantiation of
> > template class 'std::__1::__is_assignable_imp<Templ8<int>::Member *&,
> > Templ8<int>::Member *&, false>' requested here
> >    : public __is_assignable_imp<_Tp, _Arg> {};
> >             ^
> > /usr/bin/../lib/c++/v1/type_traits:2616:38: note: in instantiation of
> > template class 'std::__1::is_assignable<Templ8<int>::Member *&,
> > Templ8<int>::Member *&>' requested here
> >    : public __is_nothrow_assignable<is_assignable<_Tp, _Arg>::value,
> > _Tp, _Arg>
> >                                     ^
> > /usr/bin/../lib/c++/v1/type_traits:2667:14: note: in instantiation of
> > template class 'std::__1::is_nothrow_assignable<Templ8<int>::Member
> > *&, Templ8<int>::Member *&>' requested here
> >    : public is_nothrow_assignable<typename
> add_lvalue_reference<_Tp>::type,
> >             ^
> > /usr/bin/../lib/c++/v1/utility:250:20: note: (skipping 9 contexts in
> > backtrace; use -ftemplate-backtrace-limit=0 to see all)
> >                   is_nothrow_copy_assignable<second_type>::value)
> >                   ^
> > /usr/bin/../lib/c++/v1/__config:253:34: note: expanded from macro
> '_NOEXCEPT_'
> > #  define _NOEXCEPT_(x) noexcept(x)
> >                                 ^
> > /usr/bin/../lib/c++/v1/memory:2386:15: note: in instantiation of
> > template class
> 'std::__1::__libcpp_compressed_pair_imp<std::__1::__tree_end_node<std::__1::__tree_node_base<void
> > *> *>,
> >      std::__1::allocator<std::__1::__tree_node<std::__1::pair<int,
> > Templ8<int>::Member *>, void *>>, 2>' requested here
> >    : private __libcpp_compressed_pair_imp<_T1, _T2>
> >              ^
> > /usr/bin/../lib/c++/v1/__tree:813:56: note: in instantiation of
> > template class
> 'std::__1::__compressed_pair<std::__1::__tree_end_node<std::__1::__tree_node_base<void
> > *> *>,
> >      std::__1::allocator<std::__1::__tree_node<std::__1::pair<int,
> > Templ8<int>::Member *>, void *>>>' requested here
> >    __compressed_pair<__end_node_t, __node_allocator>  __pair1_;
> >                                                       ^
> > /usr/bin/../lib/c++/v1/map:711:22: note: in instantiation of template
> > class 'std::__1::__tree<std::__1::pair<int, Templ8<int>::Member *>,
> > std::__1::__map_value_compare<int, Templ8<int>::Member *,
> >      std::__1::less<int>, true>,
> > std::__1::allocator<std::__1::pair<int, Templ8<int>::Member *>>>'
> > requested here
> >    typedef typename __base::__node_traits                 __node_traits;
> >                     ^
> > main_bug.cpp:9:22: note: in instantiation of template class
> > 'std::__1::map<int, Templ8<int>::Member *, std::__1::less<int>,
> > std::__1::allocator<std::__1::pair<const int, Templ8<int>::Member
> > *>>>'
> >      requested here
> >    typedef typename map<K,Member*>::iterator iterator_type;
> >                     ^
> > main_bug.cpp:13:17: note: in instantiation of template class
> > 'Templ8<int>' requested here
> >    Templ8<int> test;
> >                ^
> > 1 error generated.
> > _______________________________________________
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> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
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