https://bugs.llvm.org/show_bug.cgi?id=38980
Bug ID: 38980
Summary: Weird failure/interaction in
substitution/specialization matching
Product: clang
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: C++
Assignee: unassignedclangb...@nondot.org
Reporter: ca...@carter.net
CC: dgre...@apple.com, llvm-bugs@lists.llvm.org
Compiling this correct program with -std=c++1z:
template<class, class> constexpr bool is_same_v = false;
template<class T> constexpr bool is_same_v<T, T> = true;
template<class...> using void_t = void;
template<class T> struct id { using type = T; };
template<class T> T val() noexcept;
template<class X, class Y> using cond_res =
decltype(false ? val<const X&>() : val<const Y&>());
template<class, class, class = void>
struct CT { using type = void; };
template<class D1, class D2>
#ifndef WORKAROUND
struct CT<D1, D2, void_t<cond_res<D1, D2>>> : id<cond_res<D1, D2>> {};
#else
struct CT<D1, D2, void_t<cond_res<D1, D2>>> {
using type = cond_res<D1, D2>;
};
#endif
struct S1 {};
struct S2 : private S1 {};
struct S3 : protected S1 {};
static_assert(is_same_v<void, CT<S1, S2>::type>); // Fine
static_assert(is_same_v<void, CT<S1, S3>::type>); // Error
produces diagnostices (https://godbolt.org/z/WGvIFN):
<source>:11:40: error: cannot cast 'const S3' to its protected base class
'const S1'
decltype(false ? val<const X&>() : val<const Y&>());
^
<source>:18:50: note: in instantiation of template type alias 'cond_res'
requested here
struct CT<D1, D2, void_t<cond_res<D1, D2>>> : id<cond_res<D1, D2>> {};
^
<source>:30:31: note: in instantiation of template class 'CT<S1, S3,
void>' requested here
static_assert(is_same_v<void, CT<S1, S3>::type>); // Error
^
<source>:27:13: note: declared protected here
struct S3 : protected S1 {};
^~~~~~~~~~~~
1 error generated.
Private base class? Fine. Protected base class? *EXPLODES*
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